JPH0286254A - Differential signal generation circuit - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to reduce the weight of a differential signal generation circuit for measuring subscriber circuit to ground unbalance of a time division switching device by using an operational amplifier without using a transformer. and a non-inverting amplifier that takes out the voltage across the terminal resistor connected to the ground at the human horn terminal from the audio frequency oscillator, and a phase inverting amplifier with a gain of 0 dB that inverts the phase of the non-inverting amplifier on the ground side, A phase rotation ensuring amplifier for canceling the phase rotation caused by the phase inverting amplifier is connected to the output side of the non-inverting amplifier, and the phase rotation ensuring amplifier and the phase inverting amplifier are in the same IC. Configure to be a property.

[Industrial application field]

The present invention relates to a differential signal generation circuit for measuring subscriber circuit-to-ground unbalance of a time division switching device.

A symmetrical signal component (current, voltage) differential signal and an asymmetrical signal component in-phase signal are generated on the communication line (two lines) of the subscriber circuit of the time division switching device. In general, voice signals are differential signals, and the power supply current is also a differential signal.However, noise induced from the outside in communication lines is often a common-mode signal.

Variations in the common mode signal in the voice band in the power supply circuit appear as ground unbalance, and the ground unbalance of 40 dB means that when 0 dB common mode noise is applied, it is converted to -40 dB differential noise. become. Therefore, by measuring the differential noise in the voice band, it is possible to measure the ground unbalance of the subscriber circuit.

The present invention is an improvement regarding the differential signal generation circuit used to measure this ground unbalance.

[Conventional technology]

FIG. 4 shows a differential signal generation circuit using a conventional transformer. In the figure, 10 is an audio frequency oscillator, 11 is a transformer, and 12 is a measurement impedance.

The audio frequency oscillator 10 generates audio frequencies 5011z to 3.・
This is an oscillator that generates 1KIIz, and the lance 11 is connected to the earth through a measuring impedance 12 from the middle point of the secondary winding. The measurement impedance 12 is Z/4 (150Ω) of the line impedance Z (600Ω).
Ω) for measuring ground unbalance.

The audio signal generated by the audio frequency oscillator 10 is applied to the primary winding of the transformer 11, and the output from the secondary winding is A.
, is sent to the B terminal, and the A terminal and the measurement impedance 1
The output signals sent between the two and between the B terminal and the measurement impedance 12 are sent to the measuring instrument as differential signals whose waveforms are symmetrically converted.

[Problem to be solved by the invention]

The conventional differential signal generation circuit described above uses a transformer for phase conversion, has a gain loss due to the 1-lance, and has poor characteristics at low frequencies. In order to improve the characteristics at low frequencies, it is necessary to increase the size of the transformer itself, which is not suitable for devices that are becoming smaller due to electronicization.

The present invention aims to reduce the size of the circuit by using an amplifier without using an L lance.

[Means to solve the problem]

FIG. 1 shows the principle configuration diagram of the present invention. In the figure, 10
is an audio frequency oscillator, 1 is a non-inverting amplifier, 2 is a phase inverting amplifier, 3 is a phase rotation guarantee amplifier, 4 is a terminating resistor, 5,
6 indicates the impedance for measurement.

An audio frequency oscillator 10 is connected between input terminal IN and the earth to generate an audio band signal. The non-inverting amplifier 1 is used for voltage hollow, and the phase-inverting amplifier 2 is used as an inverting amplifier with a gain of 0 dB. The phase rotation guarantee amplifier 3 is a guarantee circuit for canceling the phase rotation caused by the inverting amplifier 2. Therefore, the phase rotation ensuring amplifier 3 has the same characteristics as the inverting amplifier 2. Measurement impedance 5 and 6
is the output terminal 0. and 0□, respectively, and are used for ground unbalance measurement.
It consists of an impedance of Z /2 (300Ω) of 600Ω).

[Effect]

The audio band signal from the audio frequency oscillator 10 is input to the input terminal IN.
, the input voltage generated across the termination resistor 4 is held by the non-inverting amplifier 1 without inverting the phase, and is output from the phase rotation guarantee amplifier 3 via the measurement impedance 5 to the output terminals 0, Send to.

Further, the output of the non-inverting amplifier 1 is input to the inverting amplifier 2, the phase is inverted with a gain of 0 dB, and the output is sent to the output terminal 02 via the measurement impedance 6. Phase rotation guarantee amplifier 3
has the same characteristics as the inverting amplifier 2 and serves as a guarantee circuit for canceling the phase rotation of the inverting amplifier 2.

Send the symmetrically phase-converted output signals from output terminals 01 and 0□ to the subscriber circuit, and measure the differential signal from this differential signal generator with a measuring instrument to measure ground unbalance. .

〔Example〕

A circuit configuration diagram of an embodiment of the present invention is shown in FIG.

In the figure, 10 is an audio frequency oscillator (OSC), 1
is a non-inverting amplifier (AMPI), and 2 is a phase-inverting amplifier (A
MP2), 3 is the phase rotation guarantee amplifier (AMP3), 4 is the terminating resistor (RO), and 5.6 is the measurement impedance (Z
/2), 7 is a differential signal generation circuit, 8 is a DC superimposition circuit,
9 indicates a subscriber circuit.

The audio frequency oscillator 10 is connected to the input terminal IN of the differential signal generation circuit 7, and the output terminal 0. A DC superimposition circuit 8 is connected to and 02, and the output side of the DC superposition circuit 8 is connected to input terminals A and B of the subscriber circuit 9. The terminating resistor RO is 600Ω,
By making the resistance values of the resistors R1 and R2 of the phase inverting amplifier 2 equal, the gain of the inverting amplifier can be set to 0 dB. Furthermore, the measurement impedance Z/2 is set to 300 Ω, which is 1/2 of the line impedance of 600 Ω.

The DC superimposition circuit 8 inputs the differential signal from the differential signal generation circuit 7 and superimposes an AC signal on the DC flowing from the A and B terminals of the subscriber circuit 9 to the series circuit of the coil L1 and the resistor R3.

Therefore, the subscriber circuit 9 can measure the DC superimposed differential signal.

The differential signal from the differential signal generation circuit 7 must have a completely symmetrical inverted signal waveform. Therefore, in the differential signal generation circuit 7, a phase rotation guarantee amplifier 3 is connected to the output side of the non-inverting amplifier 1 and the input side of the phase inverting amplifier 2 as a guarantee circuit for canceling the phase rotation caused by the phase inverting amplifier 2. output terminal 0. via measurement impedance 5. Output to. The phase rotation guarantee amplifier 3 uses an operational amplifier in the same IC to have the same characteristics as the phase inversion amplifier 2. This causes output terminal 0. The differential signal sent out from and 0□ can send out a completely symmetrical waveform signal with no phase lead or lag.

As an example, the relationship between the gain and phase of an operational amplifier is shown in the characteristic diagram of FIG. In the figure, the upper diagram shows the characteristics between the frequency and the amplification degree of the operational amplifier, and the lower diagram shows the relationship between the frequency and the phase associated with this.

The solid line shows the theoretical characteristics and the dotted line shows the actual waveform. The figure shows the relationship between a situation where the gain drops due to a change in frequency and a situation where the phase shifts. Let 〇 be the set gain to the amplification degree, and set the frequency where the gain drops by 3 dfl at frequency [2 to 10.
lz, when the phase shift is 0° at the frequency f2, the phase shift of the operational amplifier changes as shown by the dotted line due to a change in frequency. Therefore, the phase rotation guarantee amplifier 3 is used to guarantee the phase shift of the operational amplifier due to this change in gain.

In the figure, 1 is a non-inverting amplifier, 2 is a phase-inverting amplifier,
3 is a phase rotation guarantee amplifier, 4 is a terminating resistor, 5.6.12
1 is a measurement impedance, 7 is a differential signal generation circuit, 8 is a DC superimposition circuit, 9 is a subscriber circuit, 10 is an audio frequency oscillator, and 11 is a transformer.

〔Effect of the invention〕

The differential signal generation circuit of the present invention is transformerless, which reduces the weight of the device, improves low-frequency characteristics, and generates differential signals without gain loss.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a circuit diagram of the embodiment, Fig. 3 is a gain and phase characteristic diagram of the operational amplifier of the embodiment, and Fig. 4 is a circuit using a conventional transformer. A configuration diagram is shown.

Claims (1)

[Scope of Claims] In a differential signal generation circuit for measuring subscriber circuit-to-ground unbalance of a time division switching device, a non-inverting amplifier that extracts the voltage across a terminating resistor connected to the ground from an input terminal from an audio frequency oscillator. (1), and a phase inverting amplifier (2) with a gain of 0 dB for inverting the phase of the non-inverting amplifier on the ground side; A phase rotation guarantee amplifier (3) for canceling phase rotation is connected and output, so that the phase rotation guarantee amplifier (3) and the phase inversion amplifier (2) have the same characteristics in the same IC. 1. A differential signal generation circuit comprising: