CN106301231A - A kind of local oscillator noise counteracting method and circuit - Google Patents

Abstract

The invention provides a method and circuit for canceling local oscillator phase noise. The circuit includes two mixers, wherein the radio frequency input terminal of the first mixer is connected to the radio frequency input signal, and the radio frequency input terminal of the second mixer is connected to a The load, the local oscillator signal source are respectively connected to the local oscillator signal input terminals of the first mixer and the second mixer, and the intermediate frequency output terminals of the first mixer and the second mixer are respectively connected to the subtractor, through The subtractor cancels the local oscillator phase noise contained in the intermediate frequency signal output by the first mixer. The invention can improve the quality of the output signal of the first mixer, and enhance the linearity and sensitivity of the output signal of the mixer when a small signal is input.

Description

A method and circuit for canceling local oscillator phase noise

technical field

The invention relates to the field of radio technology, in particular to a method and circuit for canceling local oscillator phase noise.

Background technique

In the field of radio technology, frequency conversion circuits composed of local oscillators and mixers are widely used in radio systems including mobile communications, satellite navigation, radar, remote sensing, signal measurement and metering.

When ideally, the local oscillator is a single frequency spectral line or the mixer is an ideal double-balanced mixer, in the case of no input at the RF input terminal, the mixer has no intermediate frequency component output. However, due to the limitations of the process, the mixer cannot achieve ideal double balance, and the spectrum of the local oscillator signal cannot achieve a single spectral line. vibration phase noise signal output. This phenomenon is especially obvious in the millimeter wave frequency band, because the signal source in the millimeter wave frequency band generally uses a frequency multiplier source. After frequency multiplication, the signal spectrum purity becomes poor, and there are large phase noise and other clutter near the carrier. Therefore, even if the RF input of the mixer is zero, the IF output of the mixer will generate an IF signal due to the multiplication of the local oscillator signal itself. This phenomenon is called mixer self-mixing. The self-mixing intermediate frequency signal will interfere with the measured intermediate frequency signal, introduce measurement errors, and reduce the sensitivity of the receiver.

Contents of the invention

In view of this, the present invention provides a method and circuit for canceling local oscillator phase noise.

Based on the embodiment of the present invention, the present invention provides a method for canceling local oscillator phase noise, the method comprising:

The local oscillator signal output by the local oscillator signal source is divided into two channels and respectively connected to the first mixer and the second mixer;

The first mixer is used as the main working mixer, and its radio frequency input terminal receives radio frequency input signal;

The second mixer is used as an auxiliary mixer for local oscillator phase noise cancellation, and its radio frequency input terminal is connected to a load;

After the two output signals of the first mixer and the second mixer are canceled by the phase noise of the subtractor, the output signal of the subtractor is output as an intermediate frequency output signal.

Further, the local oscillator phase noise signal output from the first mixer output terminal is canceled by adjusting the amplitude of the local oscillator phase noise signal output from the second mixer output terminal.

Further, a first isolator is added between the first mixer and the local oscillator signal source, and a second isolator is added between the second mixer and the local oscillator signal source, so as to reduce radio frequency signal crosstalk.

Further, the local oscillator signal output by the local oscillator signal source is divided into two channels through the power divider, and respectively connected to the input terminals of the local oscillator signal of the first mixer and the second mixer.

Further, the local oscillator signal output by the local oscillator signal source is divided into two paths through the directional coupler, the main arm of the directional coupler is input to the first mixer, and the output signal of the side arm of the directional coupler is input to the second mixer through the amplifier. Mixer.

Based on the embodiment of the present invention, the present invention provides a local oscillator phase noise cancellation circuit, the circuit comprising: a first mixer, a second mixer, a local oscillator signal source, and a subtractor;

The local oscillator signals output by the local oscillator signal source are respectively input to the local oscillator signal input terminals of the first mixer and the second mixer;

The radio frequency input terminal of the first mixer receives a radio frequency input signal;

The radio frequency input terminal of the second mixer is connected to a load;

The signals output from the output terminals of the first mixer and the second mixer are connected to the subtractor, and the signals at the two output terminals of the first mixer and the second mixer are canceled by the subtractor for local oscillator phase noise After that, the output signal of the subtractor is output as an intermediate frequency signal.

Further, the subtractor is provided with an amplitude adjustment circuit, and the amplitude adjustment circuit is used to adjust the amplitude of the local oscillator phase noise signal output by the second mixer, so that the local oscillator phase output by the output terminal of the second mixer The amplitude of the noise signal is equal to the amplitude of the local oscillator phase noise signal output from the output terminal of the first mixer, so as to cancel the local oscillator phase noise output from the output terminal of the first mixer.

Further, the circuit further includes: a first isolator, one end of which receives the local oscillation signal, and the other end is connected to the local oscillation signal input end of the first mixer; and

One end of the second isolator receives the local oscillator signal, and the other end is connected to the local oscillator signal input end of the second mixer.

Further, the circuit further includes: a power divider, which is used to divide the local oscillator signal output by the local oscillator signal source into two paths, which are respectively connected to the input terminals of the local oscillator signal of the first mixer and the second mixer .

Further, the circuit further includes: a directional coupler, which is used to divide the local oscillator signal output by the local oscillator signal source into two paths, and the output signal of the main arm of the directional coupler is connected to the local oscillator signal input of the first mixer terminal, the output signal of the side arm is connected to the input terminal of the amplifier; and

The amplifier is used to amplify the output signal of the side arm of the directional coupler, and its output terminal is connected to the local oscillator signal input terminal of the second mixer.

The cancellation circuit of the local oscillator phase noise provided by the present invention includes two mixers, wherein the first mixer is used as the main working mixer (main mixer), and its radio frequency input terminal is connected to the radio frequency input signal, and the second mixer is used as the main working mixer (main mixer). The RF input terminal of the mixer is connected to a load, the local oscillator signal source is respectively connected to the local oscillator signal input terminals of the first mixer and the second mixer, and the intermediate frequency output terminals of the first mixer and the second mixer The subtractors are respectively connected, and the local oscillator phase noise contained in the output signal of the first mixer is canceled through the subtractors. The invention can improve the quality of the output signal of the first mixer, and enhance the linearity and sensitivity of the output signal of the mixer when a small signal is input.

Description of drawings

FIG. 1A is a circuit schematic diagram of a double-balanced mixer;

Fig. 1B is a circuit schematic diagram of a double-balanced mixer working in the positive half cycle of the local oscillator signal;

Fig. 1C is a circuit schematic diagram of a double-balanced mixer working in the negative half cycle of the local oscillator signal;

FIG. 2 is a schematic structural diagram of a local oscillator signal canceling circuit provided by an embodiment of the present invention;

3 is a schematic structural diagram of the principle structure of the subtraction circuit in the local oscillator signal cancellation circuit provided by an embodiment of the present invention;

4 is a schematic structural diagram of a circuit principle in a local oscillator signal canceling circuit with an isolator provided by an embodiment of the present invention;

FIG. 5 is a schematic structural diagram of a circuit principle in a local oscillator signal canceling circuit with a power divider provided by an embodiment of the present invention;

FIG. 6 is a schematic structural diagram of a circuit principle in a local oscillator signal canceling circuit using a directional coupler provided by an embodiment of the present invention.

detailed description

In order to make the purpose, technical solutions and advantages of the present application clearer, the solutions described in the present application will be further described in detail below with reference to the accompanying drawings. When the following description refers to the accompanying drawings, the same numerals in different drawings refer to the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with aspects of the present application as recited in the appended claims.

The terminology used in this application is for the purpose of describing particular embodiments only, and is not intended to limit the application. As used in this application and the appended claims, the singular forms "a", "the", and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It should also be understood that the term "and/or" as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

It should be understood that although the terms first, second, third, etc. may be used in this application to describe various information, the information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of the present application, first information may also be called second information, and similarly, second information may also be called first information. Depending on the context, the word "if" as used herein may be interpreted as "at" or "when" or "in response to a determination."

Please refer to Figure 1 for the basic principle of the double-balanced mixer, where Figure 1A is the circuit of the mixer, and Figure 1B and Figure 1C are the circuits when the mixer works in the positive half cycle and negative half cycle of the local oscillator signal respectively.

The current and voltage I-V characteristics of the diode can be expressed by formula (1)

i＝a ₀ +a ₁ u+a ₂ u ² (1)

The high-order term is ignored in the formula, because the high-order term signal generated after frequency mixing can be filtered out after a low-pass filter. For the positive half cycle of the local oscillator, the voltage signal on the two diodes D1 and D3 is

u ₁ =u ₀ +u _s

(2)

u ₃ ＝u ₀ -u _s

In the formula, u ₀ and u _s are local oscillator signal and radio frequency signal respectively. The diode D1 and D3 current signal is

i ₁ ＝a _d1-0 +a _d1-1 (u ₀ +u _s )+a _d1-2 (u ₀ +u _s ) ²

(3)

i ₃ ＝a _d3-0 +a _d3-1 (u ₀ -u _s )+a _d3-2 (u ₀ -u _s ) ²

The output signal of the intermediate frequency terminal of the mixer is

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}\\ <span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>\\ <span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\\ <span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ]</span>\\ <span\; class="notranslate">\; \&ap;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; ]</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In the formula, (a _d1-1 +a _d3-1 )≈2a ₁ ; (a _d1-2 +a _d3-2 )≈2a ₂ . For an ideal situation, the IV characteristics of diodes D1 and D2 are the same, and the access paths of D1 and D2 are equal in length; the center tap of the coil is at the center position, etc., at this time, Δa ₀ =0, Δa ₁ =0, Δa ₂ = 0, the IF output of the double-balanced mixer contains only difference frequency (ω ₀ -ω _s ) and sum frequency (ω ₀ +ω _s ) items in addition to the RF signal, namely

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\\ <span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

The actual mixer is not an ideal device, and Δa ₀ , Δa ₁ , and Δa ₂ are all non-zero, resulting in local oscillator phase noise signals at the IF output of the mixer. Commercial mixers give the isolation between local oscillator and intermediate frequency and local oscillator and radio frequency, which is generally 20dB to 30dB. If Δa ₁ is used to represent all unideal components, assume that Δa ₁ is -25dB; 2a ₂ is the frequency conversion loss, generally It is about 6dB.

When the local oscillator has an interference signal e ₀ near the carrier, the intermediate frequency output of the mixer is

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}\\ <span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>\\ <span\; class="notranslate">\; \&ap;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formula (6) that the output of the IF terminal of the mixer includes the IF, local oscillator, radio frequency, and the sum of radio frequency and local oscillator frequency. After the low-pass filter, only the 4R _L a ₂ u ₀ u _s and 2R _L Δa ₂ u ₀ e ₀ yield the IF term and Suppose the frequency conversion loss 2a ₂ is about -6dB; Δa ₂ ≈ Δa ₁ , that is, Δa ₂ is also -25dB, then Δa ₂ is 19dB lower than 2a ₂ , when e ₀ is equal to the signal at the RF input terminal of the mixer, e ₀ is measured The maximum error introduced by the intermediate frequency signal is 11%. The so-called maximum error refers to the maximum error introduced when e ₀ is in phase or reverse phase with the RF signal. In other phases, the error becomes smaller. The influence of the crosstalk signal e ₀ on the measurement can be expressed by formula (7)

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 8.69</span>}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}}\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In the formula, P _n and P _s respectively define the level of the clutter signal output at the intermediate frequency of the mixer and the measured intermediate frequency signal. It can be seen from formula (7) that when the amplitude of the radio frequency signal becomes smaller, the influence of the interference signal on the intermediate frequency signal output by the mixer will become larger.

Based on the above analysis, it can be seen that since the mixer cannot achieve ideal double balance and the non-single spectral line of the local oscillator signal spectrum, the self-mixing of the mixer is caused. Therefore, when there is no input at the RF input terminal, the mixing There will be local oscillator phase noise signal output at the intermediate frequency output terminal of the device. In order to suppress the influence of the phase noise of the local oscillator on the intermediate frequency signal output by the mixer, and improve the linearity and sensitivity when receiving or measuring small signals through the mixer, the present invention provides a method and circuit for canceling the phase noise of the local oscillator. The circuit structure diagram of Fig. 2, this circuit comprises local oscillator signal source LO, first mixer M1, the second mixer M2, subtractor S, and this method comprises the following steps:

Step 100, the local oscillator signal output by the local oscillator signal source LO is divided into two channels and respectively connected to the first mixer M1 and the second mixer M2;

Step 102, using the first mixer M1 as the main working mixer, and its radio frequency input terminal receives the radio frequency input signal RF;

Step 104, using the second mixer M2 as an auxiliary mixer for local oscillator phase noise cancellation, and connecting its radio frequency input end to a load LOAD;

Step 106: After the intermediate frequency signals output by the two mixers of the first mixer M1 and the second mixer M2 are canceled by the subtractor S for local oscillator phase noise, the output signal of the subtractor is used as the intermediate frequency output signal.

Please refer to the example in Figure 2, the canceling circuit of the local oscillator phase noise provided by the present invention includes two mixers, wherein the first mixer is used as the main working mixer for actual work, and its radio frequency input terminal is used to receive the actual The external radio frequency input signal is processed, and the second mixer is used to cancel the local oscillator phase noise contained in the output signal of the first mixer, and the radio frequency input terminal of the second mixer is connected to a load. Based on the previous analysis of the self-mixing principle of the mixer, both mixers include the local oscillator phase noise generated by self-mixing The local oscillator phase noises in the output signals of the two mixers are correlated, and the invention creatively uses the output of the second mixer to cancel the correlated local oscillator phase noise contained in the output signal of the first mixer, thereby The quality of the intermediate frequency output signal of the first mixer is improved, and the linearity and sensitivity of the mixer output signal are improved when a small signal is input.

In one embodiment of the present invention, the subtractor implements the circuit structure as shown in Figure 3, and in this embodiment, a high-precision operational amplifier is used to realize the original signal of the two signals output by the two mixers. The offset processing of vibration and phase noise, the output signals of the two mixers can be respectively connected to the non-inverting and inverting input terminals of the operational amplifier, or the inverting and non-inverting input terminals of the operational amplifier according to the application scenario, and the output of the operational amplifier is used as the output of the phase subtractor signal output.

Further, due to the difference in the balance performance of the two mixers, there will also be a difference in the amplitude of the local oscillator phase noise contained in the output signals of the two mixers. In order to further reduce the influence of the local oscillator phase noise, in the example of the present invention An amplitude adjustment circuit is added to the subtractor. In this circuit, the output terminal of the first mixer, that is, the main working mixer, is connected to the inverting input terminal of the operational amplifier, and the second mixer is the auxiliary one for offsetting. The output terminal of the mixer is connected to the non-inverting input terminal of the operational amplifier through an adjustable potentiometer. In this embodiment, the function of the adjustable potentiometer is to adjust the signal amplitude so that the amplitudes of the local oscillator phase noise signals input into the operational amplifier by the two channels are equal, so as to accurately cancel the local oscillator phase contained in the output signal of the first mixer purpose of noise.

In order to prevent the RF signal from forming crosstalk after passing through the mixer, in the embodiment of the present invention, please refer to the example in Figure 4, add the first isolator ISO1 between the first mixer M1 and the local oscillator signal source LO, and add the first isolator ISO1 between the A second isolator ISO2 is added between the mixer M2 and the local oscillator signal source LO.

In the embodiment of the present invention, please refer to the example in Fig. 5, the local oscillator signal is divided into two by the power divider DIV, and the two output signals of the power divider DIV are respectively input to the first mixer M1 and the second mixer The input terminal of M2, among them, the function of adding a power divider is to divide the local oscillator signal into two signals. In the case of limited amplitude of the local oscillator signal source, it is not enough to drive the mixer after being attenuated by the power divider , you can choose a directional coupler as a power splitter.

In an embodiment of the present invention, the signal input to the first mixer is a millimeter-wave frequency band greater than 50 GHz, and the level of the local oscillator signal is limited, and it is not enough to drive the mixer after being attenuated by a power divider, so 10dB directional coupling is used As shown in Figure 6, the main arm of the directional coupler CUP is input to the first mixer M1, and the side arm output of the 10dB directional coupler CUP is input to the second mixer M2 through the millimeter wave amplifier AMP, and the second mixer The radio frequency input terminal of the device M2 is connected with a waveguide load LOAD, and the canceling principle of the phase noise of the local oscillator is referred to the above analysis process, and will not be repeated here. Since the phase noise output by the mixer is only a function of the relationship between the local oscillator carrier and the phase noise, although the local oscillator takes different paths and different electrical lengths, it does not affect the correlation of the intermediate frequency outputs of the two mixers.

Since the amplitude of the local oscillator phase noise output by the mixer (that is, the output signal after the self-mixing signal is superimposed with noise) is small, it is inconvenient to observe whether it is completely cancelled. Combined with the example in Figure 3 above, in order to adjust the subtractor circuit to make the two outputs The amplitudes of the two are equal to achieve the purpose of offsetting the phase noise of the local oscillator output by the measurement mixer. Therefore, the following means can be used to adjust the amplitude adjustment circuit in the subtractor: In the state where the RF input of the first mixer is turned off, Set the local oscillator signal source to AM output, set the modulation signal frequency to the required intermediate frequency frequency, and the modulation depth to 0.5%. At this time, the output signal of the mixer is relatively large. In the state of large signal, adjust the subtractor circuit so that the subtractor The output of the circuit is minimum. After adjustment, the local oscillator closes the modulation and restores the continuous wave output.

Through the actual circuit test, the local oscillator phase noise cancellation method and circuit provided by the invention can improve the phase noise of the intermediate frequency output of the mixer by more than 20dB, and improve the linearity and sensitivity of small signal measurement. The local oscillator phase noise cancellation method provided by the present invention can be used in the design of receivers and radars to improve the linearity and sensitivity of measuring small signals; it can also be used in signal analysis and measurement devices to reduce the influence introduced by local oscillator phase noise; it can also be used for phase noise The measuring device reduces the influence introduced by the phase noise of the local oscillator.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the present invention. within the scope of protection.

Claims (10)

1. A method for canceling local oscillator phase noise, characterized in that the method comprises: The local oscillator signal output by the local oscillator signal source is divided into two channels and respectively connected to the first mixer and the second mixer; The first mixer is used as the main working mixer, and its radio frequency input terminal receives radio frequency input signal; The second mixer is used as an auxiliary mixer for local oscillator phase noise cancellation, and its radio frequency input terminal is connected to a load; After the two output signals of the first mixer and the second mixer are canceled by the phase noise of the subtractor, the output signal of the subtractor is output as an intermediate frequency output signal. 2 . The method according to claim 1 , wherein the local oscillator phase noise signal output from the first mixer output terminal is canceled by adjusting the amplitude of the local oscillator phase noise signal output from the second mixer output terminal. 3 . 3. The method according to claim 1, wherein a first isolator is added between the first mixer and the local oscillator signal source, and a second isolator is added between the second mixer and the local oscillator signal source. isolator to reduce RF signal crosstalk. 4. The method according to claim 1, 2 or 3, characterized in that, the local oscillator signal output by the local oscillator signal source is divided into two paths through a power divider and connected to the first mixer and the second mixer respectively The input terminal of the local oscillator signal. 5. The method according to claim 1, 2 or 3, wherein the local oscillator signal output by the local oscillator signal source is divided into two paths by a directional coupler, and the main arm of the directional coupler is input to the first mixer , the output signal of the side arm of the directional coupler is input to the second mixer through the amplifier. 6. A canceling circuit of local oscillator phase noise is characterized in that the circuit comprises: a first mixer, a second mixer, a local oscillator signal source, and a subtractor; The local oscillator signals output by the local oscillator signal source are respectively input to the local oscillator signal input terminals of the first mixer and the second mixer; The radio frequency input terminal of the first mixer receives a radio frequency input signal; The radio frequency input terminal of the second mixer is connected to a load; The signals output from the output terminals of the first mixer and the second mixer are connected to the subtractor, and the signals at the two output terminals of the first mixer and the second mixer are canceled by the subtractor for local oscillator phase noise After that, the output signal of the subtractor is output as an intermediate frequency signal. 7. The circuit according to claim 6, wherein an amplitude adjustment circuit is arranged in the subtractor, and the amplitude adjustment circuit is used to adjust the amplitude of the local oscillator phase noise signal output by the second mixer, so that The amplitude of the local oscillator phase noise signal output from the second mixer output terminal is equal to the amplitude of the local oscillator phase noise signal output from the first mixer output terminal, thereby canceling the local oscillator phase noise output from the first mixer output terminal. 8. The circuit of claim 6, further comprising: The first isolator, one end of which receives the local oscillator signal, and the other end connected to the local oscillator signal input end of the first mixer; One end of the second isolator receives the local oscillator signal, and the other end is connected to the local oscillator signal input end of the second mixer. 9. The circuit according to claim 6, 7 or 8, wherein the circuit further comprises: The power divider is used to divide the local oscillator signal output by the local oscillator signal source into two channels, which are respectively connected to the input terminals of the local oscillator signal of the first mixer and the second mixer. 10. The circuit according to claim 6, 7 or 8, wherein the circuit further comprises: The directional coupler is used to divide the local oscillator signal output by the local oscillator signal source into two channels. The output signal of the main arm of the directional coupler is connected to the local oscillator signal input port of the first mixer, and the output signal of the side arm is connected to the Amplifier input; The amplifier is used to amplify the output signal of the side arm of the directional coupler, and its output terminal is connected to the local oscillator signal input terminal of the second mixer.