JPH0261803B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a frequency conversion circuit that converts a high frequency signal into a low frequency signal by performing harmonic mixing using a sampler. When applying a high frequency signal to a test element (e.g. capacitor, resistor, amplifier, etc.) to measure the high frequency characteristics of the element, the output signal of the test element should be converted to a low frequency signal to facilitate the measurement. Generally, measurements are carried out using FIG. 1 is a block diagram of a conventional frequency conversion circuit. In the figure, the sampler 3 is connected to the output signal 4 of the input high-frequency signal source 1 (at frequency f _O , e.g. from an amplifier,
signals passed through test elements such as capacitors and resistors) and the output signal 6 of the sample pulse generator 13
(sample frequency f _S ) to generate an output signal 10 of frequency f _M '. Here, the output signal 6 of the sample pulse generator 13 is generated using a phase lock loop (PLL) circuit 2.
The PLL circuit 2 includes a sampler 5 that performs harmonic mixing of the signals 4 and 6, a phase detector 7 that receives the output signal of the sampler 5 and a reference signal (frequency f _M ) 8, and a phase detector 7 that passes through a low-pass filter 9. A voltage-controlled variable frequency signal generator (VCO) 11 receives the output signal of the VCO 11, and a sample pulse generator 13 receives the output signal of the VCO 11 and generates a pulse signal.
Consisted of. The PLL circuit 2 operates so that the output frequency of the sampler 5 becomes equal to _fM . Here, the output of the sample pulse generator 13 is the frequency
Since it is a pulse signal with a narrow f _S width, it contains many harmonic components. Therefore, the frequency f _M ′ of the output signal 10 of the sampler 3 becomes f _M ′=f _M =f _O ±nf _S (n is the sample order or harmonic order and is a natural number). Therefore, if the difference component is extracted with a filter, the input high frequency f _O
can be converted into a constant low frequency f _M . However, this circuit has two drawbacks: Input frequency f _O
When the PLL circuit 2 changes, time is required for the PLL circuit 2 to synchronize in order to obtain the corresponding frequency _fS .
n in the above equation is not uniquely determined, and the input frequency is the same
Frequency conversion is also performed at f _O with a different order n. Since the sampling efficiency changes when the order n changes, errors occur in the amplitude and phase information of the output signal with respect to the input signal of the sampler 3. Furthermore, if the order n is unknown, the amount of compensation for changes in sampling efficiency cannot be determined. Although there is a conventional circuit that uniquely determines the sample order, it is extremely complicated. The present invention has been made to eliminate the above-mentioned drawbacks, and the main object of the present invention is that even if the input frequency changes, the synchronization time to obtain the necessary sample frequency signal is almost zero, and the input frequency remains the same. An object of the present invention is to provide a frequency conversion circuit that always performs frequency conversion with the same sample order. Another object of the present invention is to provide a frequency conversion circuit that can uniquely set the sample order to any natural number. The present invention will be explained in detail below using the drawings. FIG. 2 is a block diagram of a frequency conversion circuit according to one embodiment of the present invention. In the figure, 21 is an input high-frequency signal source (frequency f _O ), and 23 is a signal generator that generates a frequency f O _{−f M} signal lower than frequency f _O by a desired constant low frequency f _M (output frequency of sampler 25). , 27 converts the output signal of the signal generator 23 to 1/N
(N is a natural number), 29 receives the output signal of the frequency divider 27 and outputs the frequency of the frequency divider.
A sample pulse generator 25 generates a narrow pulse signal with a frequency equal to _f
It is a sampler that generates f _M ′). The frequency conversion circuit with the above configuration operates as follows. The output frequency f _S of the sample pulse generator 29 and the frequency divider 27 is f _S (f _O −f _M )/N. The output frequency f _M ′ of the sampler 25 is f _M ′=f _O =f _O ±n·f _S =f _O ±n·f _O −f _M /N (n is the sampling order and a natural number). Here sampler 2
There are multiple frequency components depending on the value of n at the output end of 5, but if a filter is connected to the output end to extract the signal component of frequency f _M , n=N
Only when , the signal f _M ′=f _M is extracted and the desired frequency conversion is performed. That is, the output signal component of frequency f _M is an output signal resulting from harmonic mixing where n=N. Here, the value of N can be uniquely set to any value, and if the same value of N is set for the same frequency f _O , the same n (=
Frequency conversion is performed using N)-order harmonic components. Furthermore, this frequency conversion circuit is an open loop circuit that applies signals from the input signal source 21 and the signal generator 23 to the sampler 25 through two paths,
Since it does not have a PLL circuit, if the input frequency _fO changes, _fS will also change at the same time. Therefore, the time required for acquisition and synchronization is almost zero, and the required sample frequency f _S signal can be obtained instantaneously. Signal source 2
By connecting a test element between 1 and the sampler 25, the high frequency characteristics of the element can be converted to low frequencies and measured. FIG. 3 is a block diagram of a frequency conversion circuit according to another embodiment of the invention, including a detailed block diagram of the signal generator shown in FIG. A portion 20 surrounded by a dotted line in the figure is a detailed block diagram of the signal generator 23. 20 is a PLL circuit, which includes an input high frequency signal source 21 and a voltage controlled variable frequency oscillator (VCO)
a mixer 39 that receives the output signal from the mixer 35; and a low-pass filter 3 that receives the output signal of the mixer 39.
7. A phase detector 31 and a phase detector 3 that receive the output signals of the low-pass filter 37 and the reference signal source 32 (which generates the desired output frequency f _M of the sampler 25).
Receive the output signal of 1 and send that output signal to VCO3
The filter 33 applies the voltage to the voltage. Therefore, the VCO 35 generates a signal f _O 〓 f _M which has a frequency different from f _O by f _M. The operation of converting _fO into _fM ' (= _fM ) is the same as in the case of FIG. In addition, in the case of this embodiment, since a PLL circuit is used which uses the output signal of the signal source 21 as one input signal,
Requires time for phase synchronization. However, n
The value of =N can be uniquely set to any value. FIG. 4 is a block diagram of a frequency conversion circuit according to yet another embodiment of the present invention. This circuit is capable of converting a wide range of input frequencies to lower frequencies. Components that are the same as those in the circuit shown in FIG. 2 are designated by the same reference numerals. 43 is a first mixer that mixes the output signals of signal source 41 (frequency f _V ) and signal source 45 (frequency f _O ) to generate a signal of frequency f; 47 is signal source 4;
1 and the output signal of the signal source 49 (frequency f _O 〓f _M ) to generate a signal of frequency f±f _M . Therefore, the output of the second mixer 47 includes the first
A signal whose frequency differs from the frequency of the output signal of mixer 43 by f _M (desired output frequency) is generated.
Here, the signal source 45 is equivalent to the signal source 21 in FIG. 2, and the signal source 49 is equivalent to the dotted line portion 20 in FIG. Here, by keeping f _O and f _O 〓f _M constant and making f _V variable, f can be varied over a wide range. Therefore, by connecting a test element between the first mixer 43 and the sampler 25, the frequency characteristics over a wide range of the element can be converted to low frequencies and measured. The frequency conversion operation is the same as in the case of FIG. 2, and only when n=N, f _M '=f _M , and the value of N can be uniquely set to any value. Also,
Since it does not use a PLL circuit that uses the output signal of the signal source 41 as an input signal, it is an open-loop circuit, and even if _fV is changed, there is no time required for pull-in or phase synchronization, and the sample pulse generator 29 generates an instant signal. The desired output signal is generated. Note that due to the operation of the sampler 25, the value of f _S has a certain range, so
When f _V is varied, the value of N is changed in conjunction. The operation of this circuit is shown below using specific numerical values.

[Table] As is clear from the above explanation, according to the present invention, the sampling order can be uniquely set to any value by the frequency division ratio of the frequency divider, and desired frequency conversion can be performed. Can be done. Further, even if the input frequency changes, such conversion can be performed instantaneously.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional frequency conversion circuit.
FIG. 2 is a block diagram of a frequency conversion circuit according to one embodiment of the present invention, and FIG. 3 is a block diagram of a frequency conversion circuit according to another embodiment of the present invention, including a detailed block diagram of the signal generator shown in FIG. 4 are block diagrams of a frequency conversion circuit according to still another embodiment of the present invention. 1, 21: Input high frequency signal source, 3, 5: Sampler, 7, 31: Phase detector, 9, 33, 37: Filter, 11, 35: Voltage controlled variable frequency oscillator, 13, 29: Sample pulse generator ,23,
32, 41: Signal source, 27: Frequency divider, 39, 4
3,47: Mixer.

Claims (1)

[Claims] 1. A first input signal source and a frequency f that is different from the output frequency f of the first signal source by a desired frequency f _M '.
A second signal source that generates a signal of -f _M , and a frequency divider that divides the output signal of the second signal source (dividing ratio = N)
a circuit that receives the output signal of the frequency divider and generates a sample pulse signal; a sampler that receives the output signal of the first signal source and the sample pulse signal and performs harmonic mixing; and the sampler. a filter for extracting the signal component of the desired frequency f _M from the output signal of the second signal source, the output signal of the second signal source is generated without using the output signal of the sampler, and the output signal of the second signal source is generated without using the output signal of the sampler; The sample order n of wave mixing is n=
A frequency conversion circuit characterized in that the frequency conversion circuit is uniquely determined by N. 2. The second signal source includes a mixer that receives the output signal of the first signal source and the output signal of the voltage-controlled variable frequency oscillator, and a mixer that receives the output signal of the mixer and the desired frequency f _M via a low-pass filter. and means for applying the output signal of the phase detector to the voltage-controlled variable frequency oscillator via a filter. The frequency conversion circuit according to claim 1, which is a signal source whose output signal is the output of a voltage-controlled variable frequency oscillator. 3. The first signal source includes a variable frequency signal source, a third signal source, and a first signal source that receives output signals of the variable frequency signal source and the third signal source and generates an output signal.
the second signal source includes the variable frequency signal source, a fourth signal source that generates a signal with a frequency different from the output frequency of the third signal source by a desired frequency f _M , and a fourth signal source that generates a signal with a frequency different from the output frequency of the third signal source by a desired frequency A variable signal source and a second mixer that receives the output signal of the fourth signal source and generates an output signal of a frequency that differs from the output frequency of the first mixer by the desired frequency f _M. Frequency conversion circuit according to range 1. 4 The fourth signal source includes a mixer that receives the output signals of the third signal source and the voltage-controlled variable frequency oscillator, and a reference that generates the output signal of the mixer via a low-pass filter and the desired frequency f _M The voltage controlled variable frequency oscillator comprises a phase lock loop consisting of a phase detector that receives an output signal from a signal source, and means for applying the output signal of the phase detector to the voltage controlled variable frequency oscillator via a filter. 4. The frequency conversion circuit according to claim 3, which is a signal source whose output signal is the output of a frequency oscillator.