JPH0690250B2 - AC signal measuring circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a measuring circuit for an AC signal, and in particular, the amplitude of the AC signal
It relates to a phase measuring circuit.

[Prior art and its problems]

Generally, the impedance or circuit of the device to be measured is applied to the device to be measured (for example, resistor, condensor or amplifier), and the relationship between the passing signal and the applied signal (for example, voltage, magnitude of current and amount of phase shift). I used a single alternating signal source to measure its own gain and phase,
The signal source in this case was extremely complicated. In order to solve this, two fractional N oscillators were used as shown in FIG. This is filed by the applicant on the same day and is described in detail in the specification entitled "Amplitude and phase measuring circuit for AC signals". That is, in the figure, 1
0 and 20 are fractional N oscillator, 30 is crystal oscillator, 12
Is the device under test (eg, resistor), 13 and 15 are samplers, 1
Reference numerals 4 and 16 are analog-to-digital converters, and 17 is a microprocessor. In this case, one of the factors of the measurement error is the jitter and phase noise of the fractional N oscillator itself. Also, it can be realized by using a crystal oscillator to obtain a high-quality output signal, but in this case the frequency of the input signal and the sampling signal is single, and it is not possible to obtain a sampling signal with any desired number of divisions. It was impossible. The fractional-N oscillator is composed of a phase-locked loop using the fractional (fractional) N technique. Here, the output frequency of the voltage-controlled oscillator (VCO) is the reference frequency applied to the phase detector. It can be multiplied by a rational number (integer + minority). This is achieved by making the frequency division ratio N of the frequency divider in the negative feedback loop equivalently rational. Details regarding the fractional N technique are disclosed in U.S. Pat. No. 3,928,813 or JP-A-51-60148.

[Object of the Invention]

The present invention has been made to eliminate the above-mentioned drawbacks.

[Outline of Invention]

According to one embodiment of the present invention, the output of the voltage controlled crystal oscillator is used as a sampling signal, and the output frequency can be set to an arbitrary predetermined value by the fractional N oscillator.

Example of Invention

FIG. 2 is an electric circuit diagram of a measuring circuit according to an embodiment of the present invention. In the figure, 30 is a crystal oscillator, 11 is a filter, and the alternating signal that has passed through the filter is introduced into the device under test 12. Here, the output signal and the input signal of the device under test 12 are applied to the respective one input ends of the samplers 13 and 15, respectively. On the other hand, the sampling signals introduced into the samplers 13 and 15 are obtained by the following means according to the present invention. That is, the output of the crystal oscillator 30 is introduced into the fractional-N oscillator 20, and its output is applied to one input end of the phase detector 21. Here, the phase detector 21 and the filter 22 and the voltage control type crystal oscillator 23 constitute a closed loop, and the output of the voltage control type crystal oscillator 23 is applied to the other input end of the phase detector 21. , The output is the sampling signal described above.

Here, the period of the signal applied to the device under test is T,
When the period of the sampling signal is t, the relationship of t = nT + T / m is provided (where m and n are positive integers and m is the number of samples). With the above signal, for example a crystal oscillator
When the output frequency of 30 is 100 MHz and the frequency of the sampling signal is set to about 1 MHz, the set frequency is determined by how many times one cycle of 100 MHz is divided. This set frequency may be set by the fractional-N oscillator 20 shown in FIG. 2 and locked by the output of the voltage-controlled crystal oscillator 23.

For example, when the division number m is 10, the frequency fs of the sampling signal is 1 / 1.001 MHz, which is 999.000999000999 kHz when converted into 16 digits. Furthermore, if the number of divisions is 1000, the frequency will be 999.990000099999000 ....
That is, the variable range of the frequency in the output signal of the voltage-controlled crystal oscillator 23 becomes narrower as the number of divisions increases, but a high-quality sampling signal with less jitter and phase noise can be obtained at any frequency. The effect is great.

[Brief description of drawings]

FIG. 1 is a principle diagram for explaining an AC signal amplitude / phase measuring circuit, and FIG. 2 is an electrical circuit diagram of an AC signal amplitude / phase measuring circuit according to an embodiment of the present invention. 30: Crystal oscillator, 12: Device under test, 13, 15: Sampler, 1
4, 16: Analog-to-digital converter, 17: Microprocessor, 20: Fractional N oscillator, 21: Phase detector, 2
3: Voltage control type crystal oscillator, 11, 22: Low pass filter.

Claims (1)

[Claims] 1. A circuit for measuring the amplitude and phase relationship between a measurement signal applied to a device under test and an output signal from the device under test, comprising a crystal oscillator for applying the measurement signal to the device under test, A second signal source that generates a signal of period t having a relationship of t = nT + T / m (where m and n are positive integers and m is the number of samples in period T), where T is the period of the measurement signal. A phase-locked loop having a voltage-controlled crystal oscillator for phase-locking the output signal of the second signal source as a reference input signal; and an output signal from the device under test from the voltage-controlled crystal oscillator. A first sampling means for sampling with an output signal; and a second sampling means for sampling a measurement signal applied to the device under test with an output signal from the voltage controlled crystal oscillator.
Sampling means, a first analog-digital converter connected to the output of the first sampling means, a second analog-digital converter connected to the output of the second sampling means, the first and second Microprocessor means for calculating the amplitude and phase relationship between the measurement signal applied to the device under test and the output signal from the device under test based on the output signal of the analog-to-digital converter. AC signal measuring circuit.