JPH0528973U - FM demodulator test equipment - Google Patents

Abstract

(57) [Abstract] [Purpose] Measure the transmission distortion of the FM demodulator under test in a short time and look directly at it. The FM signal generator 21 outputs an FM wave obtained by modulating a phase-locked signal of a predetermined frequency with a signal of a modulation frequency having the same accuracy as that of crystal oscillation. The local signal generator 24 digitally sweeps the frequency of the local signal output from the local signal source 25 having a synthesizer configuration. The output unit 27 mixes the FM wave and the local signal and outputs the FM wave whose carrier wave is swept to the FM demodulator 5 under test. The demodulated signal from the FM demodulator 5 under test is input to the modulated signal removing section 31, and the signal obtained by removing the signal component of the modulation frequency from the demodulated signal and the original demodulated signal are respectively detected by the detecting section 32. . Both detected signals are output to the comparison unit 33, and the ratio between the detected signals is calculated as transmission distortion. The calculated transmission distortion is displayed on the display unit 34 in association with the carrier frequency.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a transmission distortion characteristic direct-viewing apparatus capable of directly looking at the distortion characteristics of an FM demodulator, and in particular, an FM for measuring and displaying a distortion characteristic represented by the following equation called a sinard value while sweeping a frequency. The present invention relates to a demodulator test device.

[Distortion D + noise N] / [fundamental wave S + distortion D + noise N]

Hereinafter, the above equation is represented by [D + N] / [S + D + N].

In the above equation, if the noise N is measured or used in a region where it does not matter, it is represented by D 1 / S + D.

[0005]

[Prior Art]

 To measure the transmission distortion of the DUT while sweeping the frequency, it is modulated as shown in "New Microwave System Analyzer" described in Anritsu Technical No. 43 (issued by Anritsu Corporation in July 1982). Conventionally, there has been a technique of preparing a transmitter for outputting a signal and a receiver for FM detection and measuring the differential gain to evaluate the distortion.

In this technique, an FM wave whose carrier wave is swept is applied from a transmitter to an object to be measured, the output from the object to be measured is detected by an FM detector, and the amplitude of the demodulated wave is detected and displayed. The relative fluctuation of the amplitude displayed in the range of the sweep frequency is expressed as the deviation value.

Further, as a method for measuring distortion by comparing a fundamental wave component included in a signal and a harmonic wave component that is a factor of transmission distortion, a harmonic distortion measuring device having a configuration shown in FIG. It was

In this harmonic distortion measuring device, an input signal containing a fundamental wave S, a harmonic wave D, and noise N is detected by one of the detectors 1a of the detecting unit 1, and the fundamental wave removing unit 2 The signal (harmonic D + noise N) from which only the fundamental wave is removed is detected by the other detector 1b, and the detection voltages from the detectors 1a and 1b are compared by the comparator 3. ..

In such a harmonic distortion measuring device, the measuring frequency is changed from point to point, and the distortion is measured by comparing the respective levels of the harmonic and the fundamental wave.

In addition, a spectrum analyzer capable of displaying the spectrum of each harmonic has been conventionally used to measure the harmonic that is a factor of signal distortion.

[0011]

[Problems to be solved by the device]

 However, with the conventional technology that measures differential phase and group delay, it is possible to measure at high speed while sweeping, but the amount of distortion is displayed as a deviation value (relative value) within the band, and the amount of distortion is displayed as a harmonic of the fundamental wave. There was an inconvenience that it could not be displayed as the power (level) of. Also, in this measurement, the signal quality of the transmitter (S / N and modulation distortion) does not have a large effect on the measurement results, so a relatively low-quality signal source is used, so It is not possible to measure the absolute amount of

Further, in the measurement by the harmonic distortion measuring device having the above-mentioned configuration, it is necessary to measure the frequency of a separate signal source for supplying a signal to the FM demodulator under test while changing the point by point, It was not possible to display the amount of distortion corresponding to the frequency of the carrier wave in a short time.

Further, in the measurement using the spectrum analyzer, it is convenient in that each harmonic component can be observed, but there is an inconvenience that the total distortion amount cannot be directly output, and the spectrum analyzer has a large internal distortion. Therefore, it was not suitable for the measurement of minute strain.

The present invention solves these problems, and provides an FM demodulator test apparatus capable of measuring the transmission distortion of an FM demodulator under test in a short time and directly looking at the distortion as a harmonic level. Has a purpose.

[0015]

[Means for Solving the Problems]

 In order to achieve the above object, an FM demodulator test apparatus of the present invention includes a phase lock circuit, and generates an FM signal that is FM-shifted with a high-accuracy modulation frequency signal around a phase-locked predetermined frequency. Section, a local signal generating section for outputting a frequency-swept local signal, and an FM wave having a carrier wave whose frequency is swept by mixing the FM-shifted signal and the local signal to the FM demodulator under test And a demodulation signal from the FM demodulator under test, which forms a transmission section with an output section for removing a component of the modulation frequency from the demodulation output from the FM demodulator under test, A demodulation signal from which only the modulation frequency component is removed from the modulation signal removal unit, and a detection unit that detects the demodulation signal over a fixed band, and the demodulation signal output by the detection unit. The magnitude of the corresponding detected signal is compared with the magnitude of the demodulated signal corresponding to the demodulated signal from which only the component of the modulation frequency is removed, and the result is output. The receiving section is composed of the display section that displays the frequency corresponding to the swept frequency.

[0016]

[Action]

 In the FM demodulator test apparatus of the present invention, the signal from the FM signal generator and the local signal from the local signal generator are mixed by the output unit, the frequency of the carrier wave is swept, and the FM wave is accurately FM-modulated to generate the FM wave. The demodulated signal transmitted to the FM demodulator under test and the signal obtained by removing the modulated signal component from the demodulated signal are respectively detected by the detection section, and the detected voltages of both are compared. The result of this comparison is displayed as a distortion amount corresponding to the frequency of the swept carrier.

[0017]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an FM demodulator test apparatus 10 according to an embodiment.

The FM demodulator test apparatus 10 is composed of a transmitter 20 that supplies a signal to the FM demodulator 5 under test and a receiver 30 that receives the output signal of the FM demodulator 5 under test.

The FM signal generator 21 of the transmitter 20 is composed of an FM modulator 22 and a modulation signal source 23, and has, for example, the circuit configuration shown in FIG.

In FIG. 2, the FM modulator 22 is composed of a VCO 22a, a frequency divider 22b, a phase detector 22c and a phase locked loop formed by a filter 22d, and locks the oscillation frequency of the VCO 22a to a predetermined frequency with the accuracy of the reference frequency. ing.

The VCO 22a is a voltage variable oscillator using a variable capacitance diode in the resonance circuit. For example, the resonance circuit is roughly coupled to the collectors of two transistors, and the collector and base of each transistor are used for feedback. By adopting a circuit configuration that is coupled via a capacitor and adjusting the operation of the two transistors to a balanced state, an oscillation signal with less modulation distortion is output.

The oscillated output is frequency-divided by the frequency divider 22b by N, and the phase is compared with the reference signal by the phase detector 22c. The output of the phase detector 22c is input to the VCO 22a via the filter 22d, and the oscillation frequency thereof is locked to N times the frequency of the reference signal.

The filter 22d is preset with a characteristic that does not respond to the frequency of the modulation signal from the modulation signal source 23.

The modulation signal source 23 outputs a modulation signal for frequency-modulating the VCO 22a.

The oscillator 23a of the modulation signal source 23 is composed of a synthesizer or a crystal oscillator in order to output a highly accurate modulation signal, and its oscillation frequency is variable.

The signal from the oscillator 23a is input to the attenuator 23b. The attenuator 23b determines the degree of modulation, that is, the amount of FM deviation, and is variable.

The output of the attenuator 23b is output to the VCO 22a via the filter 23c. The filter 23c is for removing the distortion of the modulation signal, and is configured so that its cutoff frequency can be changed.

From the FM signal generation unit 21 configured as described above, an FM wave FM-modulated by the modulation signal from the modulation signal source 23 is centered on the frequency locked to N times the frequency of the reference signal. , Is output with a small amount of distortion and the remaining amount FM.

Returning to the description of FIG. 1, the local signal generator 24 of the transmitter 20 is composed of a local signal source 25 and a sweep controller 26. The local signal source 25 is composed of a frequency synthesizer capable of high-speed digital sweep and capable of obtaining measurement accuracy.

The sweep control unit 26 digitally sweeps the output frequency of the local signal source 25, and outputs the data acquisition timing and the sweep frequency information to the receiving unit 30 side.

The output unit 27 of the transmitting unit 20 converts the carrier wave of the FM wave from the FM signal generating unit 21 by the mixer 27a into the desired carrier wave by converting the carrier wave of the FM wave from the frequency of the signal from the local signal generating unit 24 to be tested. Output to the FM demodulator 5.

The demodulated signal from the FM demodulator 5 under test is input to the receiving section 30. If there is no distortion in the FM demodulator 5 under test, the demodulated signal has the same waveform as the modulated signal of the modulated signal source 23 of the transmitter 20 and has a magnitude corresponding to the FM deviation amount. If the FM demodulator under test 5 is distorted, the demodulated signal contains the fundamental wave S, the distortion D, and the noise N. This demodulated signal is output to the receiving unit 30.

The receiving section 30 is composed of a modulated signal removing section 31, a detecting section 32, a comparing section 33 and a display section 34, and the specific configuration of each section except the display section 34 is shown in FIG.

The configuration of the receiving unit 30 will be described below with reference to FIG.

The demodulated signal from the FM demodulator 5 under test is input to the modulated signal removing section 31 and the detecting section 32.

The demodulated signal input to the modulated signal removing unit 31 is output to the ATT 31b after only the modulated signal is removed by the band elimination filter 31a having a narrow band characteristic.

The band of the band elimination filter 31a is set to a narrow range that can be ignored as compared with the constant band detected by the detection unit 32, and as shown in the characteristic A of FIG. _m It has an extremely high removal characteristic for the signal component B of.

When the S / N of the signal on the transmission side is poor and the modulated signal has a fluctuation component (apparent frequency fluctuation), the band of the demodulated signal is expanded as shown by the dotted line in FIG. As a result, the part that cannot be removed by the band elimination filter 31a is output, and this component becomes noise, which adversely affects the measurement. However, as described above, the transmitter 20 of this device has an extremely high S / N ratio. The adverse effect of this noise is reduced by the configuration that outputs the FM wave.

The ATT 31b is a step attenuator for setting the level of the signal input from the band elimination filter 31a to the detection unit 32 within a level range in which the detection characteristic of the detection unit 32 has good linearity, and will be described later. The input or output level of the converter 33a is detected, and the level range is automatically adjusted to an attenuation amount within a predetermined range.

The detector 32 detects the demodulated signal from the FM demodulator 5 under test as it is in a fixed band, and outputs a detection voltage (that is, S + D + N), and the modulation signal remover 31. It has a detector 32b that detects a signal from which the modulation signal has been removed from the demodulated signal and outputs the detected voltage (that is, D + N). The detector voltages of both detectors 32a and 32b are output via the switch 32c. Switching output. The detector 32 may be configured to be switched and used by one detector.

The signal detected by the detector 32 is input to the comparator 33.

The comparator 33 performs logarithmic conversion on the two detection voltages [S + D + N] and [D + N] by the logarithmic converter 33a, and outputs the output of the logarithmic converter 33a to the A / D converter 33d. Is converted into digital data and stored in the memory 33c.

The digital conversion of the A / D converter 33d and the updating of the address of the memory 33c are performed by the information from the local signal generator 24.

The data processing unit 33d calculates [D + N] / [S + D + N] for each sweep frequency based on the data [S + D + N] and [D + N] stored in the memory 33c, and outputs the result. When the two detectors are used in parallel like the detector 32, the comparing unit 33 calculates [D + N] based on [D + N] and [S + D + N] simultaneously output from the two detectors. ] / [S + D + N] can also be configured to perform an analog operation.

The calculation result of the comparison unit 33 is input to the display unit 34 as shown in FIG.

The display unit 34 displays the value of [D + N] / [S + D + N] corresponding to the swept carrier frequency, as shown in C of FIG. In FIG. 5, the horizontal axis represents the carrier frequency and the vertical axis represents the value of [D + N] / [S + D + N] in dB.

[S + D + N] (that is, the level of the entire demodulated signal) and [D + N] / [S + D + N] are simultaneously output from the comparison unit 33, and both of them are displayed by the display unit 34 in correspondence with the carrier frequency. If shown, the carrier frequency characteristics of the entire demodulated signal and the distortion level can be observed simultaneously on the screen.

[0049]

[Effect of the device]

 As described above, the FM demodulator test apparatus of the present invention applies the FM wave whose carrier wave is swept and which is modulated with a highly accurate modulation signal to the FM demodulator under test and outputs the demodulated signal. Since the harmonic distortion is measured and displayed, the transmission distortion of the FM demodulator under test can be directly viewed as the harmonic level, and the S / N can be swept well and measured in a short time. is there.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed circuit configuration of a main part of one embodiment.

FIG. 3 is a block diagram showing a detailed circuit configuration of a main part of one embodiment.

FIG. 4 is a diagram for explaining characteristics of a main part of the embodiment.

FIG. 5 is a diagram showing a display example of measurement results of one example.

FIG. 6 is a block diagram showing a configuration of a conventional device.

[Explanation of symbols]

 5 FM demodulator under test 10 FM demodulator test device 20 transmitter 21 FM signal generator 22 FM modulator 23 modulation signal source 24 local signal generator 25 local signal source 26 sweep controller 27 output unit 30 transmitter 31 modulation signal Removal unit 32 Detection unit 33 Comparison unit 34 Display unit

[Procedure amendment]

[Submission date] November 27, 1991

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Fig. 2]

[Figure 4]

[Figure 1]

[Figure 3]

[Figure 5]

[Figure 6]

Claims (1)

[Scope of utility model registration request] 1. An FM including a phase-locked circuit, which is a signal of a highly accurate modulation frequency centered around a phase-locked predetermined frequency.
An FM signal generator (21) that generates a shifted signal, a local signal generator (24) that outputs a frequency-swept local signal, and a frequency sweep that mixes the FM-shifted signal and the local signal. An output section (27) for outputting an FM wave having the generated carrier wave to the FM demodulator under test, and a modulation signal removing section (31) for removing only the component of the modulation frequency in the demodulation output from the FM demodulator under test. ), And a demodulation signal from the FM demodulator under test and a demodulation signal from the modulation signal removal unit from which only the component of the modulation frequency has been removed, over a fixed band, respectively.
2) and the magnitude of the detected signal corresponding to the demodulated signal output from the detector and the magnitude of the demodulated signal corresponding to the demodulated signal from which only the component of the modulation frequency has been removed, and the result is output. A transmission distortion characteristic direct-viewing device comprising: a comparison unit (33); and a display unit (34) that displays the result output by the comparison unit in correspondence with the swept frequency of a carrier wave.