JPH03261876A - Method of measuring electronic circuit - Google Patents

Abstract

PURPOSE:To perform an accurate measurement in a short time by composing a simple measuring circuit of a DC voltmeter, a control circuit, a variable DC voltage source and a variable capacity diode and controlling an output voltage applied from the variable DC voltage source to the variable capacity diode. CONSTITUTION:The output of a signal source 1 is made zero and the output voltage of an output terminal 23 is measured by a DC voltmeter 7 when a demodulation circuit 2 has no input. A measured valve is outputted from a measuring output terminal 71 to be inputted to the input terminal 81 of a control circuit 8, being made its reference value. The control circuit 8 calculates a difference between the reference value and the measured value of the DC voltage and outputs a control signal corresponding to the difference from an output terminal 82. As a result, the capacity of a variable capacity diode 10 changes and a resonant frequency f0 and an input carrier frequency fc finally agree with each other whereby a synchronization can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for measuring electronic circuits including AM or FM signal demodulation circuits.

2. Description of the Related Art In general, an AM or FM demodulation circuit measures the demodulated output characteristics after tuning the frequency of an unmodulated input signal.

A conventional method for measuring electronic circuits including AM or FM demodulation circuits will be described below.

FIG. 2 is a block diagram showing a conventional electronic circuit including an AM or FM demodulation circuit, in which 1 is a signal source, 2 is a demodulation circuit, and input terminals 21. Resonance terminal 22. It has an output terminal 23. 3 is a capacity, 4 is an AC voltmeter, 5 is a capacity, and 6 is a variable coil.

In the above configuration, a human input signal from the signal source 1 is input to the input terminal 21 of the demodulation circuit 2, and the input signal is tuned by the capacitor 5 and variable coil 6 connected to the resonance terminal 22. The tuned signal demodulates the modulated wave component in the signal into the original signal.

The demodulated signal is outputted from the output terminal 23 of the demodulation circuit 2, and the DC component of the demodulation circuit 2 is removed by the capacitor 3, leaving only the AC component. The AC voltage level of the signal containing only AC components is measured by an AC voltmeter 4.

Problems to be Solved by the Invention However, in order to accurately measure the demodulation output characteristics of the demodulation circuit 2 with the above conventional configuration, it is necessary to adjust the carrier frequency f of the human signal.
c, the resonance frequency f of the capacitor 5 and the variable coil 6.

need to be synchronized.

This tuning has a resonance frequency f determined by f=1/(2πfi). This is a task of matching the carrier frequency f0 of the input signal by increasing or decreasing the inductance of the variable coil 6.

Taking FM demodulation as an example, the input frequency flN shown in FIG.
and the DC voltage V at the output terminal. The point at which the slope of the demodulated output characteristic curve becomes maximum is at the resonant frequency f. and the resonance frequency f when the input carrier frequency f0 is not modulated. If they do not match, accurate demodulation output characteristics cannot be measured.

Therefore, when measuring the demodulated output characteristics of an AM or FM demodulation circuit, tuning is essential even in mass production. However, tuning by increasing/decreasing the inductance of the variable coil 6, which is performed in the conventional circuit, is based on the carrier frequency f from the signal source 1. When a signal with constant modulation frequency f, , and modulation depth M is input to the input terminal 21 of the demodulation circuit 2, the ferrite core of the variable coil 6 is manually rotated, and the output terminal 22 of the demodulation circuit 2 is inputted to the input terminal 21 of the demodulation circuit 2. This is done by adjusting the AC voltage level of the demodulated output signal outputted from the AC voltmeter 4 and transmitted through the capacitor 3 to the AC voltmeter 4, so that the tuning accuracy depends on the width of the linearity of the demodulated output characteristic. It is influenced by the operator who performs the adjustment, and the time required for synchronization is also long.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for measuring electronic circuits, which solves the above-mentioned conventional problems, and allows appropriate measurements to be made with simple operations.

Means for Solving the Problems In order to achieve this object, the method for measuring an electronic circuit of the present invention comprises a tuning circuit composed of a DC voltmeter, a control circuit, a variable DC voltage source, and a variable capacitance diode, and a demodulation circuit. Measure the DC voltage at the output terminal when there is no input to the circuit with a DC voltmeter,
Using the measured value as a reference value for the control circuit, the control circuit changes the voltage from the variable DC voltage source to the variable capacitance diode according to the difference between the measured value of the DC voltage at the output terminal of the demodulation circuit when the signal is not modulated manually and the reference value. It controls the applied output voltage, adjusts the capacitance of the variable capacitance diode to the optimum value, and works to match the LC resonance frequency with the human power frequency.

Effect: Due to the above structure, the tuning accuracy is not affected by factors such as the slope of the demodulation characteristic curve, the width of the linearity, and the skill level of the operator. Furthermore, since this is a tuning method in which the tuning circuit has a reference value that converges, tuning can be performed in an extremely short time compared to manual tuning, and the demodulation output characteristics of the demodulation circuit can be accurately measured.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a method for measuring an electronic circuit according to an embodiment of the present invention.

In FIG. 1, 7 is a DC voltmeter and has a measurement output terminal 71. 8 is a control circuit, and input terminals 81 . It has an output terminal 82. 9 is a variable DC voltage source and has a control terminal 91.

10 is a variable capacitance diode.

Further, 1 is a signal source, 2 is an input terminal 21. A demodulation circuit having a resonance terminal 22 and an output terminal 23, 3 a capacitor, 4 an AC voltmeter, 5 a capacitor, and 6 a variable coil, which are the same as the conventional configuration.

The operation of the method for measuring an electronic circuit according to an embodiment of the present invention configured as described above will be described below. The output of the signal source 1 is set to zero, and the DC output voltage of the output terminal 23 of the demodulation circuit 2 when there is no input is measured with the DC voltmeter 7, and the measured value is outputted from the measurement output terminal 71, and the output of the control circuit 8 is Input terminal 8
1 and used as a reference value for the control circuit 8. Next, from the signal source l, the input terminal V8 and the manual carrier frequency f. An unmodulated signal with a constant value is input to the demodulation circuit 2 from the input terminal 21. At this time, the output terminal 23 of the demodulation circuit 2 has a resonance frequency f due to the capacitor 5 connected to the resonance terminal 22 of the demodulation circuit 2, the variable coil 6, and the variable capacitance diode 10. A DC voltage appears depending on the difference between the input carrier frequency fc and the input carrier frequency fc. This D
The C voltage is measured by the DC voltmeter 7 , and the measured value is output from the measurement output terminal 71 and input to the input terminal 81 of the control circuit 8 . The control circuit 8 calculates the difference between the reference value and the measured value, outputs a control signal corresponding to the difference from the output terminal 82, and inputs it from the control terminal 91 of the variable DC voltage source 9.

The variable DC voltage source 9 changes its output voltage in response to a control signal input to a control terminal 91 . The capacitance of the variable capacitance diode 10 changes as the voltage applied from the variable DC voltage source 9 changes. By changing the capacitance of the variable capacitance diode 10, the resonant frequency f determined by the capacitor 5, the variable coil 6, and the variable capacitance diode 10 changes, and finally the resonant frequency f. and the input carrier frequency f. match and synchronization can be achieved.

As described above, according to this embodiment, the demodulated output characteristics can be accurately measured in a short time by tuning to a clear reference value.

Effects of the Invention The present invention automatically performs accurate measurements by performing tuning using a simple measurement circuit composed of a DC voltmeter, a control circuit, a variable DC voltage source, and a variable capacitance diode.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a method for measuring an electronic circuit according to an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional method for measuring an electronic circuit, and FIG. 3 is an FM demodulation characteristic diagram. 1... Signal source, 2... Demodulation circuit, 3.
... Capacity, 4 ... AC voltmeter, 5 ...
...Capacity, 6...Variable coil, 7...
・DC voltmeter, 8... Control circuit, 9...
- Variable DC voltage source, 10...variable capacitance diode.

Claims (1)

[Claims] In measuring the demodulation output characteristics of an electronic circuit including an AM or FM signal demodulation circuit, a tuning circuit consisting of a DC voltmeter, a control circuit, a variable DC voltage source, and a variable capacitance diode is used. Using the DC voltage when there is no input as a reference, the control circuit controls the variable DC voltage source according to the difference between the DC voltage when the non-modulated signal is input and the reference value, and changes the voltage applied to the variable capacitance diode. and changing the frequency of the tuned circuit by changing the capacitance of the variable capacitance diode.