JPS62241423A - High-speed clamping circuit - Google Patents

Abstract

PURPOSE:To shorten a signal break time based upon the coupling time constant between a high-voltage system circuit and a low-voltage system circuit by constituting the output circuit of the high-voltage system circuit by using a two-way output voltage buffer which has current-source and current-sink ability and providing a two-way voltage clamper to the input of the low-voltage system circuit. CONSTITUTION:Both detection currents obtained by detecting voltages on the B-line and A-line sides of the high-voltage system circuit connected to a telephone set 1 are summed up at the output point of a current mirror 4 and a voltage proportional to the two wire voltages is detected across a resistance R3 and inputted to the two-way output buffer 6 which has the current-source and current-sink ability. The two-way clamper 7 is connected to the input circuit of the low-voltage system circuit composed of an input resistance Rs, a resistance R4, and an operational amplifier 5. In this constitution, the charging/discharging time of coupling capacity Cs is ended within the time of the time constant determined by the coupling capacitor Cs, the output resistance of the buffer 6, and the on resistance of the clamper 7 against large-amplitude transient variation in DC level at the time of the hook operation of the telephone set, and consequently both said resistances are set much smaller than the resistance Rs to shorten the time of a break of a signal due to the conduction of the clamper 7.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a signal interface circuit between a high-voltage circuit and a low-voltage circuit, such as a subscriber circuit of a telephone exchange, and in particular, to a signal interface circuit for overvoltage input caused by a coupling time constant. This invention relates to a high-speed clamp circuit suitable for voltage clamping.

[Background of the invention]

In subscriber circuits of conventional telephone exchanges, a high voltage power supply (V, = -aaV) is used in the DC power supply circuit section that is connected to the subscriber line to supply talking current to telephones. A low voltage power supply ('CC'III = ±5F) is used in the circuit portion that performs signal processing, and the high voltage circuit and the low voltage circuit are generally capacitively coupled. However, in a signal transmission system that transmits signal components from a high-voltage circuit to a low-voltage circuit via capacitive coupling, if the time constant due to this coupling capacitance is large, temporary fluctuations may occur in the DC level of the high-voltage circuit. This is due to the problem that the input of the low voltage circuit is saturated and the signal is interrupted.

Conventional examples of the signal transmission system of the subscriber circuit of this type of telephone exchange include, for example, "Design of a BSH circuit LSI with variable power supply characteristics" described in Nu 547, Proceedings of the 1981 National Conference of the Institute of Electronics and Communication Engineers, etc. can be mentioned.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-speed clamp circuit that solves the problems of the prior art described above and reduces the signal interruption time due to the coupling time constant between a high voltage circuit and a low voltage circuit.

[Summary of the invention]

The present invention focuses on the fact that the signal interruption time can be shortened by speeding up the charging and discharging time of the capacitor that connects the output of the high voltage circuit and the input of the low voltage circuit. By configuring the output circuit with multiple bidirectional output voltage buffers with current source and current sink capabilities, and by providing a bidirectional voltage clamper at the input of the low voltage circuit, the charging and discharging period of the coupling capacitor operated by the bidirectional voltage clamper can be reduced. This is a high-speed clamp circuit that aims to reduce the transient coupling time constant of 100 kHz to speed up charging and discharging), thereby shortening the signal interruption time.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 is a circuit diagram of a 2-wire to 4-wire conversion section of a subscriber circuit showing a first embodiment of a high-speed crank circuit according to the present invention.

In FIG. 1, 1 is a telephone, 2, 5.4 is a current mirror A #'1 mAm.

5 is an operational amplifier, and 6 is a bidirectional output voltage buffer.

7 is a bidirectional voltage clamper. B and A are each B,
Connection point of A@@, R1#R1j Ra s Ra is a resistor, Dl # Dl s Dl # Di is a diode,
Qt, Qt is output C.

transistor, to the coupling capacitance, R8 is the input resistance %'BB (
-asV) is a high voltage power supply, Vcc (5V), 'El
l(-sJ/) is a low voltage power supply. Figure 2 (α),
(a) is an equivalent circuit diagram of each current mirror 2 and 5.4 in FIG. 1. In Figures 2(a) and (A),
QB s ('4 eQw-Qa is a transistor. Figure 2 (a) shows the current shiller of P%p type (current source type) consisting of PnP transistors Qs and Qa, and Figure 2 (A) shows the current shiller of %p type (current source type). It is a current mirror of the %p% type (current sink type) made up of half-shaped transistors Qm-Q*, and outputs the same output current OUT as each input current IN.

The voltage on the B line side (connection point B) of the high voltage circuit connected to the telephone 1 in Fig. 1 is detected by the current mirror 2 to the resistor, and the voltage on the A line side (connection point A) is detected by the resistor 4. It is detected by the current mirror 3. This rain detection current is added at the output point of the current mirror 4, and two
Line voltage (voltage vB proportional to the voltage between connection points A and B is detected and becomes the input voltage ν1 of the bidirectional output voltage buffer 60. Connection points A and E are the connection points of the telephone 1, so the high voltage power supply V,... = -48V is used, so the phone 10 on hook (loop off).

The two-wire voltage changes depending on off-hook (loop on).

Diode D1 mD* and output transistor Q*, Qm
constitutes a bidirectional output voltage buffer 6 with current source and current sink capability, which forms the output circuit of a high voltage circuit, and adds a diode D1 eD, using a complementary transistor to the output transistor QlaQ, to achieve AH class. Has bidirectional output characteristics of operation. The coupling capacitor C is a capacitor that couples the bidirectional output voltage buffer of the output of the high voltage circuit and the input of the next low voltage circuit in an alternating current manner. Diode D
l s Di constitutes a bidirectional voltage clamper 7 that is connected between the coupling capacitor C1 and the ground to protect the input of the low voltage circuit. Input resistor R8, resistor R, and operational amplifier 5 are connected to low voltage power supply 'CC = 5' mV, =++ -5V
This is an input circuit for low-voltage circuits that are used.

Figure 3 shows on-hook on the telephone 1 side of Figure 1.

FIG. 7 is a waveform diagram showing transient response characteristics of large amplitude voltage fluctuations of each circuit portion that occur in response to off-hook.

In Fig. 3, tlB is the input voltage of the bidirectional output voltage buffer 6 (voltage of the resistive island VB), #03 is the charging voltage of the coupling capacitor Cj, 5 is the current of the coupling capacitor C8, and Di is the input voltage of the low voltage circuit. It is. To explain the operation of FIG. 1 with reference to FIG. 3, when the telephone 1 of FIG. 1 is on-hook,
Since the load current of the telephone 1 is 0, the input voltage ν1 of the bidirectional output voltage buffer 60 (voltage of the resistor R) becomes almost Or as shown in the diagram m5, and at this time, the charging voltage of the coupling capacitor C5 is The current of the coupling capacitor C8 and the input voltage V of the low voltage circuit are also O as shown in FIG. When the telephone 1 changes from this state to off-hook, load current suddenly flows to the telephone 1, so the bidirectional output voltage buffer 60 input voltage 1
As shown in FIG. 5, 1B rapidly decreases to, for example, -15F. At this time, the coupling capacitor C5 also starts to be charged as the voltage decreases, and the charging voltage s+5 also decreases to, for example, -15V as shown in FIG. 5, but since the output resistance of the output transistor Q8 is sufficiently low, the diode D , → Coupling capacitor C5 → Transistor Q, as shown in Figure 3, a large charging current i of coupling capacitor C8 flows through the emitter route of transistor Q, and the charging of coupling capacitor C8 ends in a short time. The head also undergoes large amplitude transient changes in a short period of time. The clamp diode D becomes conductive only for a very short time while this charging current i is flowing, and the input voltage V of the low voltage circuit also changes as shown in Fig. 3, for example -
r: 1.7V, but during this conduction period t, signal transmission from the high voltage circuit to the low voltage circuit is interrupted. Then, when the telephone 1 goes on-hook again, the load current of the telephone 1 suddenly stops flowing, and the voltage vE suddenly returns to approximately Or as shown in FIG. At this time, the coupling capacitance C3 also begins to discharge as the voltage IJB rises, and the charging voltage υ also rises to become Or as shown in FIG.
As shown in Fig. 3, a large discharge current i5 of the coupling capacitance C8 flows through the route of emitter → coupling capacitance C5 → diode D4,
The discharge of the coupling capacitor C5 ends in a short time, and the charging voltage ν and the discharge current i5 also undergo large amplitude transient changes in a short time.

Only for a very short time while this discharge current i5 is flowing, the clamp diode D becomes conductive, and the input voltage V of the low voltage circuit also becomes, for example, +α7r as shown in Fig. 3.
Signal transmission from the high voltage circuit to the low voltage circuit is interrupted during this conduction period t.

In this way, large amplitude transient fluctuations in the DC level can be handled by combining the coupling capacitor C8, the output resistance R of the bidirectional output voltage buffer 6 at the output of the high voltage circuit, and the bidirectional voltage clamper 7 at the input of the low voltage circuit. The charging/discharging time of the coupling capacitor C1 can be completed in the time constant d', = C, CRo+RoN) determined by the on-resistance R6H of the output resistor R6 and the on-resistance R61 of the input circuit of the low voltage circuit. If it is set sufficiently smaller than the input resistor R8, it becomes possible to suppress interruption of signal transmission due to conduction of the bidirectional voltage clamper 7 within a very short time. Output transistor Q1 of the bidirectional output voltage buffer 6 of the above-mentioned high voltage circuit.
The reason why Q* is set to AB class operation is to operate so that its output resistance R6 always appears low regardless of any voltage fluctuation; in simple B operation, the output transistor Q
When switching the operation of x n (h, Kf?), a period occurs in which both transistors Qt and Qt are temporarily turned off, causing a problem in which the charging and discharging time of the coupling capacitor C8 is prolonged.

As described above, in the embodiment according to the present invention, in a signal transmission system that transmits a signal component of a high voltage circuit to a low voltage circuit via capacitive coupling, the output circuit of the high voltage circuit is connected to the bidirectional output voltage buffer 6. By providing a bidirectional voltage clamper 7 at the input of the low voltage circuit, the coupling time constant τ2=C8(Ro+RoN
) and the coupling time constant τ, =C8 during small amplitude steady state, it is possible to shorten the interruption time of small signal transmission during large amplitude transient change), and in the conventional case, large amplitude transient Since the coupling time constant during a change and the coupling time constant during a small amplitude steady state are the same, it was not possible to shorten the interruption time of small signal transmission during a large amplitude transient change.

FIG. 4 is a circuit diagram of a bidirectional voltage clamper 7 having a low voltage circuit input, showing a second embodiment of the island speed clamp circuit according to the present invention. In FIG. 4, Q and rmQa are transistors. Note that the same reference numerals or symbols indicate the same or corresponding parts throughout the drawings. The bidirectional voltage clamper 7 in Figure 4 is a diode DS sD4 in Figure g1.
This is a configuration in which the transistor Qt-(h) is changed. According to this embodiment, the operation of the transistors Qt-Qs enables voltage clamping with an even lower on-resistance R6N.

FIG. 5 is a circuit diagram of a bidirectional voltage clamper 7 for low voltage circuit input, showing a third embodiment of the high speed clamp circuit according to the present invention. In FIG. 5, Qo, Qt. +Q11
, Q□ is a transistor, 'Ig'! is a constant current source, V1
t□2□, 8. , □ is the reference voltage source.

I.

The bidirectional voltage clamper 7 in FIG. 5 is a constant current source.

I, respectively, are transistors Q,,QL. For the bias current of transistor ('11 mQs*), the emitter potential of transistor Q9 and the emitter potential of transistor ('o) can be made equal, so the clamp voltage on the negative voltage side can be set by the reference voltage source VR□2□, and similarly The configuration is such that the clamp voltage on the positive voltage side can be set using the basic voltage source 'R1! Become.

FIG. 6 is a circuit diagram of a bidirectional voltage clamper 7 for low voltage circuit input, showing a fourth embodiment of the high speed clamp circuit according to the present invention. In FIG. 6, Dl and D are diodes. The bidirectional voltage clamper 7 of FIG. 6 connects the diodes D, D, of FIG. 6 to the low voltage power supply 'cc=+5V, V, instead of making the diode D3D of FIG. 1 conductive to ground level. □, = -5V is configured to conduct. According to this embodiment, the input voltage V of the low voltage circuit
, becomes higher than the low voltage power supply Vcc=+5V, the diode D becomes conductive and clamps the input voltage ν to a potential up to the power supply Vcc−+5V, and the input voltage IJi becomes the low voltage power supply V.

When the voltage drops by =g#V, the diode D6 becomes conductive and operates to clamp the input voltage V to a potential up to the power supply V, . . . =-#V.

As described above, according to the embodiment of the present invention, in a signal transmission system that transmits a signal component of a high voltage circuit to a low voltage circuit via capacitive coupling, a current sink that outputs a signal of the high voltage circuit; A bidirectional output voltage buffer with current source capability, a coupling capacitor that AC-couples the bidirectional output voltage buffer and the low voltage circuit input, and a coupling capacitor connected between the coupling capacitor and the ground to connect the low voltage circuit input. A high-speed clamper is configured to protect the bidirectional output voltage buffer and the bidirectional voltage clamper from the effects of transient DC level fluctuations in the high voltage circuit on signal transmission to the low voltage circuit input. ) The charging and discharging of the coupling capacitance can be accelerated and converged in a short time.

In the above embodiment, wire 2-4 of the subscriber circuit of the telephone exchange
Although the case where the present invention is applied to a line converter has been described, the high-speed clamp circuit according to the present invention is not limited to this.

〔Effect of the invention〕

As described above, according to the high-speed clamp circuit of the present invention, the signal interruption time due to the coupling time constant is shortened in the signal transmission system that transmits the signal component of the high voltage circuit to the low voltage circuit via capacitive coupling. Therefore, if it is used in a 2-wire to 4-wire conversion section of a subscriber circuit of a telephone exchange that constitutes this type of signal transmission system, it will have the effect of improving the service function for subscriber terminals of the telephone exchange.

[Brief explanation of drawings]

1 shows a first embodiment of a high-speed clamp circuit according to the present invention; 2 is an overall circuit diagram; FIG. 2 is an equivalent circuit diagram of each current mirror 2, 5, and 4 in FIG. 3 is a side view of the operation waveforms of each part during the transient change in FIG. 1, FIG. 4 is a circuit diagram of a bidirectional voltage clamper showing a second embodiment of the present invention, and FIG. FIG. 6 is a circuit diagram of a bidirectional voltage clamper showing an embodiment of the present invention.
FIG. 2 is a circuit diagram of a bidirectional voltage clamper showing an embodiment of the present invention. 1... Telephone 2.3.4... Current mirror 5... Operational amplifier 6... Bidirectional output voltage buffer 7... Bidirectional voltage clamper length S R1-R6... Resistor... input resistance,
-D6...Diode Q1~Q1! ...Transistor C8...Coupling capacitance V□...High voltage power supply 'CC,'l□...Low voltage power supply 1. - Representative Patent Attorney Katsutoshi Ogawa 11 Figure Time t→

Claims (1)

[Claims] In a signal transmission system that transmits signal components from a high-voltage circuit to a low-voltage circuit via capacitive coupling, a bidirectional output voltage buffer with current sink and current source capabilities that outputs a signal from the high-voltage circuit; It consists of a coupling capacitor that AC-couples the bidirectional output voltage buffer and the low voltage circuit input, and a bidirectional voltage clamper that is inserted between the coupling capacitor and the low voltage circuit input to protect the low voltage circuit input. In order to reduce the influence of transient DC level fluctuations in the high voltage circuit on the low voltage circuit input, the bidirectional output voltage buffer and the bidirectional voltage clamper speed up the charging and discharging of the coupling capacitor and converge in a short time. A high-speed clamp circuit configured as follows.