JPH05114823A - Frequency mixer circuit - Google Patents

Abstract

PURPOSE:To provide the frequency mixer circuit which consists of a small number of elements and can operate with even a low voltage. CONSTITUTION:Transistors(TR) Q1 and Q2 are an unbalanced differential couple of TRs whose common connected emitters are set to a K:1 size ratio (K>1) and a constant current source I0 is driven, but a 1st AC signal (voltage VIN) is applied to the base of the Q1 and a 2nd AC current (voltage VLO) is applied to the base of the Q2. Here,-IC1=(alphaFI0+DELTAI)/2 and IC2=(alphaFI0-DELTAI)/2 hold and IC1-IC2=DELTAI includes the components of the sum of and difference between two frequencies fIN and fLO. The components of the sum of and difference between the two frequencies fIN and fLO are converted by a load resistance RL into voltages because of V0=VCC-RLIC2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency mixer circuit, and more particularly to a frequency mixer circuit formed on a bipolar integrated circuit.

[0002]

2. Description of the Related Art In a conventional frequency mixer circuit, as shown in FIG. 2, a first frequency signal (voltage V _IN ) is applied to a reference voltage V _F of a current source (Q13) of a differential amplifier (Q11, Q12). A structure in which they are superposed and a second frequency signal (voltage V _LO ) is applied to the paired inputs of the differential amplifier, or, as shown in FIG. 3, a first input of an analog multiplier 31 such as a Gilbert multiplier. The first frequency signal (voltage V _IN ) to the pair
Is applied, and the second frequency signal (voltage V _LO ) is applied to the second input pair. Hereinafter, each circuit will be described in order.

In FIG. 2, the current characteristic of the junction diode which constitutes the transistor is expressed by Equation 1. In addition,
In Equation 1, I _E is the emitter current, I _S is the saturation current, q is the unit electron charge, V _BE is the base-emitter voltage, k is the Boltzmann constant, and T is the absolute temperature.

[0004]

[Equation 1]

Here, if V _T = kT / q, then V _BE >>
V _T. Therefore, in Expression 1, exp (V _BE /
If V _T ) >> 1, the emitter current I _E can be approximated as in Equation 2.

[0006]

[Equation 2]

At this time, the collector current I _C13 of the transistor Q13 becomes as shown in the equation (3).

[0008]

[Equation 3]

Then, when the constant current source I ₀ is set as shown in equation 4, the collector current I _C13 becomes as shown in equation 5.

[0010]

[Equation 4]

[0011]

[Equation 5]

Further, the input voltage V _LO is, as shown in Equation 6, the base-emitter voltage V of the transistor Q11.
Base-emitter voltage V of _BE11 and transistor Q12
It is the difference of _BE12 .

[0013]

[Equation 6]

[0014] Therefore, Equation 7 V _BE11 and V _BE12, I _S11 assuming, also with Equation 7 in the same 8 as the 8 and I
Assuming that _S12 is equal as shown in Equation 9, Equation 6
The input voltage V _LO can be expressed by Equation 10.

[0015]

[Equation 7]

[0016]

[Equation 8]

[0017]

[Equation 9]

[0018]

[Equation 10]

When α _F is the current amplification factor, the sum of collector currents I _C11 and I _C12 is given by equation 11.

[0020]

[Equation 11]

As a result, from the equations 10 and 11, the collector currents I _C11 and I _C12 are obtained as the equations 12 and 13.

[0022]

[Equation 12]

[0023]

[Equation 13]

Therefore, the difference current ΔI ₁ between the two collector currents can be expressed by Equation 14.

[0025]

[Equation 14]

Here, tanhx is expressed as in Expression 15, exp x is expressed as in Expression 16, and when Expression 14 is expanded using this, Expression 17 is obtained and the difference current ΔI ₁ is obtained. Includes the term of the product V _IN · V _LO of the input voltage V _IN and the same V _LO .

[0027]

[Equation 15]

[0028]

[Equation 16]

[0029]

[Equation 17]

Therefore, if the input voltage V _IN is set as in Equation 18 and the input voltage V _LO is set as in Equation 19, the product V _IN · V _LO becomes Equation 20 and the sum and difference of two frequencies (f _IN , f _L0 ) The ingredients of Then, as is clear from Equation 20, the factor that defines the frequency characteristic is the frequency characteristic (f _T ) of the transistor used exclusively. That is, the frequency mixer circuit has good high frequency characteristics.

[0031]

[Equation 18]

[0032]

[Formula 19]

[0033]

[Equation 20]

Here, if I _C11 and I _C12 are differential currents, these are expressed by the following equations 21 and 22, respectively.
(1/2) ΔI ₁ is included. In other words, I _C11 and I _C12
Should be converted into voltage. In FIG. 2, I _C12 is converted into a voltage by the load resistance R _L.

[0035]

[Equation 21]

[0036]

[Equation 22]

Next, in FIG. 3, the output voltage V _O is expressed by the equation 23. In addition, in Formula 23, A is unity gain.

[0038]

[Equation 23]

By substituting the equations 18 and 19 into this, the equation 24 similar to the equation 20 is obtained, and the one using the analog multiplier 31 is also a frequency mixer circuit.

[0040]

[Equation 24]

[0041]

The conventional frequency mixer circuit described above has the following problems. First, in the circuit shown in FIG. 2, it is difficult to superimpose a signal on the constant current source. Further, in the circuit shown in FIG. 3, since the circuit configuration of the multiplier has a large number of transistors, NF deteriorates and good high frequency characteristics cannot be obtained unless the circuit current is increased.

An object of the present invention is to provide a frequency mixer circuit capable of reducing the deterioration of NF and obtaining good high frequency characteristics with a small current consumption.

[0043]

In order to achieve the above object, the frequency mixer circuit of the present invention has the following configuration. That is, the frequency mixer circuit of the present invention includes: a differential pair transistor including two transistors each having a different emitter size; and a constant current source that drives the differential pair transistor. The first AC signal is applied to the base of the transistor,
A second AC signal is applied to the base of the other transistor;

[0044]

Next, the operation of the frequency mixer circuit of the present invention constructed as described above will be described. In the present invention, one differential pair transistor composed of two transistors having different emitter sizes, that is, a so-called unbalanced differential pair transistor is mainly configured. Therefore, the number of circuit elements can be reduced, and the deterioration of NF can be reduced. Further, since it can be operated at a low voltage, good high frequency characteristics can be obtained with a small current consumption.

[0045]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a frequency mixer circuit according to an embodiment of the present invention. The frequency mixer circuit basically includes one differential pair transistor (Q1, Q2) and a constant current source I ₀ for driving the differential pair transistor, and one transistor Q1 has a base (first ) AC signal (voltage V _IN )
Is applied to the base of the other transistor Q2 (second
AC signal (voltage V _LO ) is applied.

Here, the transistors Q1 and Q2 form an unbalanced differential pair transistor in which the sizes (areas) of commonly connected emitters are different, and the emitter size ratio is Q1: Q2 = K: 1 ( K> 1), and the operation will be described below.

The voltage V ₁ is converted into the input voltage V _{IN as} shown in Equation 25.
And the difference voltage of V _LO is the same as the difference voltage V ₁
Is the difference between the base-emitter voltage of both transistors.

[0048]

[Equation 25]

[0049]

[Equation 26]

Here, the base-emitter voltages of both transistors are the same as those in the equations 7 and 8 and the equations 27 and 2 are the same.
It can be represented by 8.

[0051]

[Equation 27]

[0052]

[Equation 28]

Since the emitter size ratio is K, the saturation currents I _S1 and I _S2 are related by the equation (29).

[0054]

[Equation 29]

Therefore, the collector current I of both transistors
The ratio of _C1 and I _C2 is given by Equation 30.

[0056]

[Equation 30]

When α _F is the current amplification factor, the constant current source I ₀ and the collector currents I _C1 and I _{C2 of} both transistors have the relationship of Expression 31.

[0058]

[Equation 31]

Therefore, the collector current I of both transistors
_C1 and I _C2 can be obtained by Equations 32 and 33.

[0060]

[Equation 32]

[0061]

[Expression 33]

Here, when K is defined as in Equation 34 using V _T and V _K according to the present invention, V _{K according} to the present invention is defined.
Can be expressed as Equation 35.

[0063]

[Equation 34]

[0064]

[Equation 35]

Then, the equations 32 and 33 can be rewritten as the equations 36 and 37, respectively.

[0066]

[Equation 36]

[0067]

[Equation 37]

Therefore, the difference current ΔI between the two collector currents can be expressed by equation 38.

[0069]

[Equation 38]

When expanded using the above-mentioned formula 15, it becomes formula 39, and the difference current ΔI includes the term of the square of the difference voltage V ₁ . This is given by Equation 25 above. Therefore, if the input voltage V _IN and the input voltage V _LO are defined by the above-described equations 18 and 19, the square of the difference voltage V ₁ is given by
It is calculated as 0.

[0071]

[Formula 39]

[0072]

[Formula 40]

That is, the difference current ΔI has two frequencies (f _IN , f
The sum and difference components of _LO ) are included. Here, since both collector currents I _C1 and I _C2 are differential currents, they can be expressed as Formulas 41 and 42, respectively.

[0074]

[Formula 41]

[0075]

[Equation 42]

Therefore, the output voltage V _O is obtained by the equation 43, and the sum and difference components of the two frequencies (f _IN , f _LO ) are the load resistance R.
Converted to voltage by _L.

[0077]

[Equation 43]

The same applies to the case where the difference current ΔI and the collector current I _C1 are converted into a voltage. In either case, a frequency mixer circuit with low current consumption and good frequency characteristics can be obtained.

[0079]

As described above, according to the frequency mixer circuit of the present invention, two different emitter sizes are used.
One differential pair transistor consisting of two transistors,
That is, since the so-called unbalanced differential pair transistor is mainly configured, it is possible to reduce the number of circuit elements and operate at a low voltage. As a result, it is possible to provide a frequency mixer circuit in which NF is less deteriorated and good high frequency characteristics can be obtained with a small current consumption.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a frequency mixer circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional frequency mixer circuit.

FIG. 3 is a circuit diagram of a conventional frequency mixer circuit.

[Explanation of symbols]

Q1 transistor Q2 transistor I ₀ constant current source V _IN input voltage V _LO input voltage V _O output voltage VCC power supply voltage

Claims (1)

[Claims] 1. A differential pair transistor comprising two transistors each having a different emitter size; and a constant current source for driving the differential pair transistor, wherein the differential pair transistor has a first base at the base of one of the transistors. A frequency mixer circuit, wherein an alternating current signal of 1 is applied and a second alternating signal is applied to the base of the other transistor.