JPS59161195A - Differential signal detecting circuit - Google Patents

Abstract

PURPOSE:To realize a monolithic IC constitution of a subscriber's circuit at a low cost by constituting a titled circuit so that only a differential signal is detected from two differential signal outputs, and the same phase noise signal is suppressed. CONSTITUTION:A two-wire differential signal current generated from a subscriber's terminal 3 flows through current mirrors 12, 13 as indicated with a full line arrow id, and an output current of the mirror 12 is current-inverted by a current mirror 14, and flows through a resistance 18 and a transistor TR17. An output current of the mirror 13 flows to a resistance 16 and a TR15. In this case, in case when resistance values of the resistances 16, 18 are made equal to each other, if the same phase noise current indicated with a dotted line ic is generated in a line resistance 4, the same phase current component inputted to the mirror 12 becomes an opposite direction, therefore, the same phase component is not generated in an output terminal 19. In the same way the same phase noise current is not generated in an output terminal 20. That is to say, only a differential signal is detected from the terminals 19, 20, and the same phase noise signal is suppressed. According to this circuit configuration, it is unnecessary to use a high resistance in order to reduce the power consumption, and an IC constitution is executed easily.

Description

[Detailed Description of the Invention] [Field of Application 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 that is installed in a subscriber circuit such as a telephone exchange and is suitable for semiconductor integrated circuit implementation.

[Prior art]

Figure 1 shows the configuration of a subscriber circuit of a telephone exchange in the prior art. In the figure, VIIE is a battery, 1 is a low impedance for direct current, and high impedance for alternating current. A current supply circuit 3 is a subscriber terminal, and is connected to the exchange side via a line resistor 4. 5 to 8 are resistors, and 9 is an operational amplifier. These constitute a differential amplifier, and are used to detect the two-wire differential signal appearing on the line side and to detect the direct current generated between the subscriber terminal 3 and the current supply circuit 1. It also detects DC voltage for loop monitoring.

According to the configuration shown in Fig. 1, the battery p-nn0 value is large (-48V), and the common-mode noise voltage generated on the 2nd wire side is large, etc., resulting in low power consumption and good common-mode noise. In order to suppress this, it is necessary to use high precision and high resistance for the resistors 5 to 8 constituting the differential amplifier, which is not suitable for fabrication into a monoseries semiconductor integrated circuit.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to convert subscriber circuits required for electronic telephone exchanges into monolithic semiconductor circuits, and to achieve high accuracy at low cost.

[Summary of the invention]

The differential signal detection circuit according to the present invention includes a 1j-th second current mirror that detects a two-wire voltage, and 1. a third current mirror that inverts the output current of the first current mirror; A pair of mutually equivalent voltage and current generators with two outputs and a reference input generate a voltage and current proportional to the current of the second current mirror, suppressing common mode noise occurring in the two-wire voltage. The current outputs of the voltage and current generators are connected together to form a differential current detection circuit, and one reference input terminal of the voltage and current generator is connected to the voltage output terminal of the other, and one voltage This device is characterized by a configuration in which a differential voltage detection output is taken out from the output terminal.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 2 to 4. FIG. 2 shows a specific configuration of the subscriber circuit, and components having the same reference numerals as those in FIG. 1 have the same functions. In Fig. 2, 10.11 is a resistor provided on the line, 12.13.14 is a current mirror, and the voltage on the B line side (indicated by terminal B) is detected by the resistor 10 and the current mirror 12. The current mirror 13 detects the voltage on the A line side (indicated by terminal A).

The specific configuration of this current mirror 12 is shown in FIG. 3 (α).
, (as shown in bl, and is proportional to the input current of 11N.
It has the function of generating an output current of 10 UT, and is composed of transistors 17'r and 2Tr fi'' (FIG. 3) connected as shown in FIG.

The specific configuration of the current mirror 13 is shown in Figure 4).
(As shown in BL-Ashi, this current mirror, 3
.

13 has characteristics complementary to the current mirror 12,
Figure 4 (as shown in Al) (trunk i'57'r,
It consists of 4Tr connected as shown.

Furthermore, in FIG. 2, 15.17 indicates a transistor, the collector of the transistor 15 is connected to the terminal 20 from which the output current 10UT'' is output, and the base is grounded. This collector is connected to the collector of the transistor 17, The emitter is connected to the base of transistor 170 via resistor 16.

The emitter of one transistor 17 is connected to a differential signal output terminal 19 via a resistor 18. transistor 17
0 base is connected to the output terminal of the current mirror 13,
The emitter of transistor 17 is connected via resistor 18 to the output terminal of current mirror '14. Furthermore, the output terminal of the current killer 12 is connected to the input terminal of the current mirror 14.

To explain the operation in the configuration as shown in FIG. 2, first, the two-wire differential signal current generated from the subscriber terminal 3 is
K, current mirror, 4 as shown in d.

12.1! The output current of the current mirror 12 is reversed by the current mirror 14, and flows through the resistor 18 and the transistor 17. The output current of current mirror 13 flows through resistor 16 and transistor 15.

That is, a voltage proportional to the current of the current mirror 13 is generated in the resistor 16, and a current equal to the current of the current mirror 13 is output from the collector of the transistor 15. Further, the base of the transistor 15 serves as a reference input that provides a reference point for the voltage drop across the resistor 16. In other words, the transistor 15 and the resistor 16 use the collector of the transistor 15 as a current output, the base as a reference input, and the resistor 16 as the collector.
It can be said that a voltage and current generator is configured in which the terminal opposite to the terminal connected to the emitter of the transistor 15 outputs a voltage.

Similarly, the circuit including the transistor 17 and the resistor 18 constitutes a voltage/current generator that generates a voltage and current proportional to the current flowing through the current mirror 14, that is, the current flowing through the current mirror 12.

The reference input terminal is a transistor 15 and a resistor 1.
6 is connected to the voltage output terminal of the voltage and current generator.

Here, if the resistance values of the resistors 16 and 18 are equal to R and the differential current fid, a voltage drop of RitL occurs with the same polarity at the resistors 16 and 18 as described above, and a difference of 2Rid occurs at the output terminal 19. A dynamic signal voltage is generated. On the other hand, since the collector currents of the transistors 15 and 17 have the same polarity, a 2id differential signal current is generated at the output terminal 20. Here, if a common mode noise current shown by the dotted line it in the diagram occurs in the line resistance 4 due to capacitive coupling, etc., the current mirror 1
Since the common mode current component input to the transistor 2 is in the opposite direction, the common mode voltage generated at the resistor 16°17 has a reverse polarity, and no common mode component is generated at the output terminal 19.
．． Since the common mode current component generated in the collector current 17 also has the opposite polarity, no common mode noise current is generated at the output terminal 20. That is, only the differential signal is detected from the two differential signal output terminals 19 and 20, and the common mode noise signal is suppressed. In the circuit configuration shown in FIG. 2, when the subscriber terminal 3 is in an open state, no current flows through the current mirrors 12 and 13.
70, the power consumption is almost zero, there is no need to use a high resistance to reduce power consumption as in the conventional example, and there is an advantage that it is easy to form a monolithic semiconductor integrated circuit. Furthermore, the mirror ratio of the current mirror 12°13 [output current (I
By appropriately selecting ovr)/input current CIIn)), it is possible to reduce the voltage fluctuation range of the output terminal 19 to a low value that is easy to integrate into a semiconductor integrated circuit.Furthermore, as mentioned above, the common mode noise at the output terminal 9 can be reduced. Since it is suppressed, there is no need to use an operational amplifier to improve the common mode suppression ability as in the conventional example, and there is also the advantage that the circuit can be simplified. Furthermore, in FIG. 2, a current output can be taken out in addition to a voltage output, which has the advantage of increasing the degree of freedom in circuit design. For example, a suitable example may be a method in which the output terminal 19 is used for detecting a two-wire signal and the output terminal 20 is used for loop monitoring detection.

In the above embodiment, the circuit component is 7.

Although the explanation was given using bipolar transistors, other functional elements (e.g. field effect transistors) and functional blocks (operational amplifier child transistors) that operate in the same way as bipolar transistors can also be used.
It is obvious that the present invention can be carried out by using a circuit configuration in which the outputs of the current mirror 13 and the current mirror 14 shown in FIG. Will.

〔Effect of the invention〕

As is clear from the embodiments described above, the present invention has the advantage that subscriber circuits such as telephone exchanges can be implemented as monolithic semiconductor integrated circuits at low cost and with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a subscriber circuit in a conventional telephone exchange, FIG. 2 is a specific circuit block diagram of a subscriber circuit showing an embodiment of the present invention, and FIG. 5 (α). (J) and FIGS. 4(α) and (A) are diagrams showing specific circuit configurations of some of the circuits shown in FIG. 2. 1... Current supply circuit 3... Subscriber terminal, 8
. 4, 10.11.16.18...Resistance 12.13.1
4 River current mirror 15.17...Transistor Vnn...Battery 1 Figure 2 Figure 15 14 3 O-(b) Mine, 41!1 3 (Tosu-) (b-606-

Claims (1)

[Claims] A differential signal detection circuit in a subscriber circuit such as a telephone exchange, in which first and second lines complementary to each other are used to detect 1 and 2 line voltages.
and a second current mirror; a third current mirror that inverts the output current of the first current mirror; and a third current mirror that inverts the output current of the first current mirror.
．． The second current mirror generates a voltage and current proportional to the current flowing through each, and includes a pair of mutually equivalent voltage and current generators having two outputs and a reference input, and generates a two-wire voltage. forming a differential current detection circuit by connecting the current outputs of the pair of voltage and current generators to each other so as to suppress common mode noise, and connecting the reference input of one of the voltage and current generators to the voltage output of the other; A differential signal detection circuit characterized in that it is configured to extract a differential voltage detection output from the one voltage output.