JPH0646756B2 - Differential signal detection circuit - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a differential signal detection circuit, and more specifically,
The present invention relates to a differential signal detection circuit which is provided in a subscriber circuit such as a telephone exchange and is suitable for semiconductor integrated circuits.

[Prior art]

FIG. 1 shows the configuration of a subscriber circuit of a telephone exchange in the prior art, in which V _BB is a battery,
1 is a current supply circuit that has a low impedance for DC and a high impedance for a differential AC signal,
A subscriber terminal 3 is connected to the exchange side via a line resistor 4. Reference numerals 5 to 8 are resistors, and 9 is an operational amplifier, which constitutes a differential amplifier, detects a line differential signal appearing on the line side, and forms a DC loop between the subscriber terminal 3 and the current supply circuit 1. It also detects the DC voltage for monitoring.

According to the configuration shown in FIG. 1, the subtraction circuit using the operational amplifier 9 constitutes a differential detection circuit, but since the value of the battery V _BB is as large as −48V, the voltage on the 2W side also becomes large, so subtraction is performed. Since a high voltage is applied to the resistance circuit (resistors 5 to 8) that constitutes the circuit, the resistance value is large (200 KΩ to 1 MΩ).
It was necessary to reduce the power consumption. On the other hand, line resistance 4
When common mode noise current is mixed in due to capacitive coupling,
This current flows into the current supply circuit 1. Current supply circuit 1
If the common-mode impedance (impedance between the line and the ground) is not sufficiently low, a common-mode noise voltage is generated on the B line and the A line. This common-mode noise voltage is harmful to signal transmission and must be suppressed. In the conventional example, since the voltages of the B line and the A line are applied to the + input and − input of the operational amplifier via the resistance circuit, it is necessary to form the resistance circuit with high accuracy in order to suppress common mode noise. As described above, it is necessary to use high precision and high resistance for the resistors 5 to 8 forming the differential amplifier, which is not suitable for forming a monolithic semiconductor integrated circuit.

[Object of the Invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a differential signal detection circuit suitable for forming a monolithic semiconductor circuit of a subscriber circuit necessary for computerizing a telephone exchange or the like.

[Outline of Invention]

A differential signal detection circuit according to the present invention includes a first current mirror for detecting a battery line voltage, a second current mirror for detecting a ground line voltage, and an output current of the first current mirror. A third current mirror that is inverted, a reference input terminal, a current input terminal, a current output terminal that outputs a current proportional to the current input to the current input terminal, and a current input terminal that is proportional to the current input to the current input terminal. A current amplifier having a voltage output terminal for outputting a voltage between the reference input terminal and a pair of first and second voltage / current generators each including a resistor connected in series, and the first voltage / current generator An output current of the third current mirror is input to a current input terminal of the voltage generator, and an output current of the second current mirror is input to a current input terminal of the second voltage current generator,
The reference input terminal of the second voltage / current generator is grounded, and the voltage output terminal of the second voltage / current generator is connected to the reference input terminal of the first voltage / current generator, and they are mutually connected. The present invention is characterized in that the connected current output terminal serves as a detection current output terminal and the voltage output terminal of the first voltage / current generator serves as a detection voltage output terminal.

Example of Invention

An embodiment of the present invention will be described in detail below with reference to FIGS. FIG. 2 shows a concrete structure of the subscriber circuit, and those designated by the same reference numerals as those in FIG. 1 have the same functions. In FIG. 2, 10 and 11 are equivalent internal resistances of the line, 12 and 13 and 14 are current mirrors, and the voltage on the B line side (battery side: shown by terminal B) by the resistor 10 and the first current mirror 12. And the resistor 11 and the second current mirror 13 are connected to the line A side (ground side:
The voltage of the terminal A) is detected.

The specific configuration of the first current mirror 12 is as shown in FIGS. 3 (a) and 3 (b), and has a function of generating an output current I _OUT proportional to the input current I _IN , and the transistor 1
Tr and 2Tr are connected as shown in FIG. 3 (b).

The specific configuration of the second current mirror 13 is as shown in FIGS. 4 (a) and 4 (b), and the second current mirror 13 has a characteristic complementary to that of the first current mirror 12. Then, as shown in FIG. 4 (b), the transistor 3T
r and 4Tr are connected as shown.

Further, in FIG. 2, reference numerals 15 and 17 denote transistors. The collector of the transistor 15 is connected to the terminal 20 from which the output current I _OUT is output, and the base is grounded. This collector is connected to the collector of transistor 17,
The emitter is connected to the base of the transistor 17 via the resistor 16. The emitter of one transistor 17 is connected to the differential signal output terminal 19 via the resistor 18. The base of the transistor 17 is connected to the current output terminal of the current mirror 13, and the transistor 17 is connected via the resistor 18.
Is connected to the current output terminal of the current mirror 14. Further, the current output terminal of the current mirror 12 is connected to the input terminal of the current mirror 14.

The operation of the differential signal detection circuit in the configuration of FIG. 2 will be supplementarily described with reference to FIG. However, here, the resistance values of the resistors 10 and 11 are equal to Ri, the resistance values of the resistors 16 and 18 are also equal to R, the A line side voltage is V _A , and the B line side voltage is V _B. The terminal 3 is equivalently represented by the internal resistance R _O and the internal signal voltage Vd ′ shown in the figure. 2-wire differential signal voltage component Vd
Is expressed by the following equation (1) from the voltage difference between the A and B lines.

Vd = V _B −V _A (1) As described above, the A line side voltage V _A is I due to the resistor 11.
_The voltage on the B line side, V _B, is converted into I _B by the resistor 10 as follows.

_{I A = V A / Ri ...} (2) I B = -V B / Ri ... (3) where the DC component (V _BB) is ignored.

On the A line side, I _A becomes the input current of the second current mirror 13, and its output current flows through the resistor 16 and the transistor 15. That is, the resistor 16 has a voltage V on the A line side.
_A voltage drop I AR that is proportional to _A occurs. Transistor 1
Current I _A which is proportional to the line A side voltage V _A from the collector 5 is output. The base of the transistor 15 is the resistor 16
It is the reference input that gives the reference point for the voltage drop of. In other words, the transistor 15 and the resistor 16 transfer the current of the second current mirror 13 through the resistor 15 to the transistor 15.
Second voltage-current generator for inputting to the emitter of the transistor 15 for current output, for inputting the base for reference input and for voltage output at the terminal of the resistor 16 opposite to the terminal connected to the emitter of the transistor 15 It can be said that it constitutes 21.

On the B line side, I _B becomes the input current of the first current mirror 12, and its output current is the third current mirror 1.
The current is inverted by 4 and flows through the resistor 18 and the transistor 17. That is, the resistor 18 is the voltage drop I _B R generated in proportion to the line B side voltage V _B. Current I _B in proportion from the collector of the transistor 17 to the line B side voltage V _B are outputted. Therefore, the circuit including the transistor 17 and the resistor 18 similarly constitutes the first voltage-current generator 22 that generates a voltage and a current proportional to the current flowing through the third current mirror 14, that is, the current flowing through the current mirror 12. ing. Then, the reference input terminal is connected to the voltage output terminal of the second voltage / current generator 21 including the transistor 15 and the resistor 16.

Ground and the voltage output terminal 23 of the second voltage / current generator 21
It has occurred the voltage drop I _A R proportional to the line A side voltage V _A between the reference input terminal of the first voltage-current generator 22 24
The voltage drop I _B R is between its voltage output terminal 19 which is proportional to the line B side voltage V _B (= voltage output terminal 23 of the first voltage current generator 21) is generated, the ground and the voltage output terminal 19 The voltage drop V _OUT between them is expressed by the following equation (4).

V _OUT = −I _B R−I _A R (4) From formulas (1), (2) and (3), formula (4) is as follows.

_{V OUT = V B R / Ri} -V A R / Ri = (V B -V A) R / Ri = VdR / Ri ... (5) (5) as represented by formula, the voltage output terminal 19V _OUT ,
A differential signal voltage proportional to the two-wire differential signal voltage Vd is generated.

On the other hand, the current at the output terminal 20 I _OUT is
From the addition of the collector currents of 5 and 17, the following is obtained using the equations (2) and (3).

I _OUT = I _B + I _A = −V _B / R i + V _A / R i = − (V _B −V _A ) / R i = −V d / R i (6) The output terminal 20 is represented by the formula (6). To I _OUT ,
A differential signal current proportional to the two-wire differential signal voltage Vd is generated.

As described above, the voltage or current addition processing is performed in order to detect the two-wire differential signal in order to effectively suppress common-mode noise induced in the communication line described below. This is because.

FIG. 6 shows a model of common-mode noise induced in the communication line. The communication line 4'is equivalently represented by the capacitance C _X to ground and the resistor R _X shown.

Although the communication line 4'in-phase noise is induced by electromagnetic induction from a power line cable or the like, this in-phase induced voltage is equivalently expressed as V _CX in the figure. The common-mode noise current i _CX flows into the communication line 4'through the ground capacitance C _X. Generally, the common mode impedance of the current supply circuit 1 is small but has a finite value (≠ 0), so that the common mode noise voltage V _C is generated between the two lines A and B and the ground. This common-mode noise voltage is also resistor 1
It is detected by 0 and 11 and the current mirrors 12 and 13, and as it is, it is mixed in the differential signal component and transmitted.
However, in the present invention, the A-line side voltage and the B-line side voltage are detected independently, and the outputs of the above-mentioned second voltage / current generator 21 and first voltage / current generator 22 are subjected to addition processing, so that this common-mode noise component is obtained. It is intended to suppress. This will be described below using mathematical expressions.

Since the common-mode noise voltage Vc is generated in both the A-line side voltage and the B-line side voltage, V _A = V _B = Vc (7) The A-line side voltage V _A is set to I _A by the resistor 11 and the B-line side voltage is set. V
_B is converted into I _B by the resistor 10 as follows.

During _{I A = V A / Ri =} Vc / Ri ... (8) I B = -V B / Ri = -Vc / Ri ... (9) above differential signal as in the case ground and the voltage output terminal 19 of the detection The voltage drop V _{OUT of} is as follows using the equation (4).

V _OUT = −I _B R−I _A R = VcR / Ri−VcR / Ri = 0 (9) As shown by the equation (9), the common mode noise voltage Vc is suppressed at the voltage output terminal 19V _OUT. It does not occur.

On the other hand, the current at the output terminal 20 I _OUT is
From the addition of the collector currents of 5 and 17, the following is obtained using the equations (2) and (3).

_{I OUT = I B + I A} = -Vc / Ri + Vc / Ri = 0 ... (10) (10) as represented by the formula, the output terminal 20 I
_Common- mode noise voltage component (Vc) is suppressed at _OUT and does not occur.

As described above, in the embodiment of the present invention, it is not necessary to set the common mode impedance of the current supply circuit to an extremely small value, and the common mode noise voltage can be suppressed without depending on the common mode impedance of the current supply circuit.

In the circuit configuration of FIG. 2, the B line voltage is once detected by the first current mirror 12 having a detection resistor between the ground and the B line, and similarly, the A line voltage is detected between the battery and the A line. Since it is detected by the inserted second current mirror 13,
When the subscriber terminal 3 is open, the current mirror 12,
Since no current flows through 13, the power consumption of the transistors 15 and 17 that generate the differential signal voltage and current becomes almost zero, and it is not necessary to make this detection resistor high resistance, and a value that facilitates integration into a monolithic semiconductor integrated circuit. (50KΩ-10
0 KΩ), there is no need to use a high resistance for power consumption reduction as in the conventional example, and there is an advantage that a monolithic semiconductor integrated circuit can be easily formed. Further, by appropriately selecting the mirror ratio [output current (I _OUT ) / input current (I _IN )] of the current mirrors 12 and 13, the voltage fluctuation range of the output terminal 19 can be set to a low value that is easily integrated into a semiconductor integrated circuit. It is possible. Further, as described above, the in-phase noises of the B line and the A line have the same amplitude and voltage addition due to opposite polarities,
Since it is canceled in the current addition process, no common-mode noise component is generated in the voltage-current generator, and it is not necessary to have a good common-mode noise suppression characteristic as in the conventional operational amplifier, and there is an advantage that the circuit becomes simple. Further, in FIG. 2, since the current output can be taken out in addition to the voltage output, there is an advantage that the degree of freedom in circuit design is increased. For example, a method in which the output terminal 19 is used for detection of a two-line audio signal and the output terminal 20 is used for detection of presence / absence of call current can be considered as a suitable example.

In the above-described embodiments, the bipolar transistor is used as the circuit constituent element, but other functional elements (for example, field effect transistor) or functional blocks (operational amplifier + transistor) that operate equivalently to this are used. It will be apparent that the present invention can also be implemented. Further, it will be apparent that the present invention can be implemented by a circuit configuration in which the outputs of the second current mirror 13 and the third current mirror 14 in FIG. 2 are interchanged.

〔The invention's effect〕

As is apparent from the above-described embodiments, the present invention has an advantage that a differential signal detection circuit suitable for making a subscriber circuit of a telephone exchange or the like into a monolithic semiconductor integrated circuit can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a subscriber circuit in a conventional telephone exchange, FIG. 2 is a concrete circuit block diagram of a subscriber circuit showing an embodiment of the present invention, FIGS. 3 (a), (b) and 4 (a) and 4 (b) are diagrams showing a specific circuit configuration of the partial circuit shown in FIG. 2, FIG. 5 is an operation explanatory diagram for the differential signal component of FIG. 2, and FIG. FIG. 7 is an operation explanatory diagram for the in-phase signal component of FIG. 2. 1 ... current supply circuit, 3,3 '... subscriber terminal, 4, R _X ... line resistance, 4' ... line, 10,11,16,18 ... resistors, 12, 13, 14 ... current mirror, 15, 17 ... Transistor, V _BB ... Battery, C _X ... Line-to-ground capacity, Vd ... 2-wire differential signal voltage, Vcx, Vc ... common-mode induced voltage, 21, 22 ... voltage / current generator, 23 ... voltage / current generator Voltage output terminal, 24 ... Reference input terminal of voltage / current generator.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Ichiro Ohikata 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Totsuka Plant, Hitachi Ltd. (72) Inventor Toshio Hayashi 3-9-11 Midoricho, Musashino-shi, Tokyo (72) Inventor, Tadakatsu Kimura, 3-9-11 Midoricho, Musashino City, Tokyo (56) Reference: Japanese Patent Laid-Open No. 56-54160 (JP, 54-54160) A)

Claims (1)

[Claims] 1. A circuit for detecting a differential signal between a ground line and a battery line in a subscriber circuit such as a telephone exchange, the first current mirror (12) for detecting a battery line voltage, and a ground. Second current mirror (13) for detecting line voltage
And a third inversion of the output current of the first current mirror
Current mirror (14), the reference input terminal (b, b '), the current input terminal (r, r'), the current output terminal (c, which outputs a current proportional to the current input to the current input terminal c '), and a pair consisting of a series connection of a resistor and a current amplifier having a voltage output terminal (r, r') for outputting a voltage proportional to the current input to the current input terminal between the voltage input terminal and the reference input terminal. The first of
A second voltage / current generator (22, 21), wherein the output current of the third current mirror is input to the current input terminal of the first voltage / current generator (22), The output current of the second current mirror is input to the current input terminal of the voltage / current generator (21), and the reference input terminal of the second voltage / current generator is grounded to generate the first voltage / current generator. The voltage output terminal of the second voltage / current generator is connected to the reference input terminal of the voltage generator, and the mutually connected current output terminals are used as the detection current output terminals, and the voltage of the first voltage / current generator is A differential signal detection circuit having an output terminal configured as a detection voltage output terminal.