JPS589628B2 - telephone circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides, in a booster type telephone circuit having a push-button dial, a second balanced circuit used to improve low-frequency sidetone during a call, which can be used both in direct current and in alternating current when dialing. This invention relates to a telephone circuit that is separated from the dial circuit so as not to affect dial characteristics.

FIG. 1 shows a conventional electric passing machine circuit having a second balanced circuit for improving low frequency sidetone.

In Figure 1, L1 and L2 are line terminals, L is a hybrid coil, N1, N2, and N3 are first, second, and third windings, T is a transmitter, Co is a DC blocking capacitor, and N
Z1 is a first balanced circuit, ZN2 is a second balanced circuit, R is a receiver, P. B. OSC. is push button dial oscillation circuit, S
W is a push-button dial common switch, and M, B, and C represent make, break, and common contacts, respectively.

Further, G1 is an automatic level adjustment circuit for a transmitting level, and G2 is an automatic level adjusting circuit for a receiving level, and the inside of the block shows an example of a circuit using a varistor.

In this telephone circuit, a second balanced circuit that improves low-frequency sidetone during calls is connected between one terminal of the third winding of the hybrid coil and the second terminal L2 of the line, as shown in the figure. Moreover, the second Heihei circuit ZN2 is composed of a resistor,
In addition, since the resistance value is as low as several hundred ohms, direct current flows through the second balance circuit even during dialing.

If the subscriber line is short and the line resistance is small, the line current is large, so even if there is a shunt to the second balanced circuit, it will have little effect on the dialing operation. However, if the subscriber line is long, the line current will be large.
Since the shunt to the balanced circuit is large, the push button dial oscillation circuit P. B. OSC. The current supplied to the oscillator will decrease, resulting in increased signal distortion and disable oscillation.

Next, suppose that the second terminal of the second balanced circuit ZN2 connected to the L2 terminal is temporarily connected to the second terminal P2 of the transmitter T (not shown), and when dialing, the pushbutton common switch SW breaks. Since it is disconnected from the L2 terminal by contact B, there is no DC bleed, and the push button dial oscillation circuit P. B. OSC.
operates stably, but the transmitter T and the second balanced circuit ZN2 are connected in series, and the second winding N2 of the hybrid coil
, are connected in parallel to both ends of the third winding N3, the dialing signal transmission level decreases and the dialing confirmation sound increases.Furthermore, since the handset is in operation, the transmission due to voice and surrounding noise is reduced. There is a drawback that variations in dial signal transmission level occur due to changes in speaker resistance.

This invention was made to solve these drawbacks, and therefore, the purpose of this invention is to improve low-frequency sidetone during calls as in the past, and to prevent DC bleed by the second balanced circuit when dialing. Therefore, it is an object of the present invention to provide a telephone circuit which realizes stable dialing operation on a long-distance line and prevention of fluctuations in dialing signal level due to changes in transmitter resistance.

The key point of the construction of the invention is that in a booster type telephone circuit having a pushbutton dial, the transmitter and the second balanced circuit are each connected to the break contact of the pushbutton dial common switch via a diode.

Next, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a telephone circuit diagram showing an embodiment of the present invention. In the figure, L1 and L2 are line terminals to which the telephone circuit is connected, and L is a hybrid coil with N, , N
2 and N3 represent the first winding, second winding, and third winding of the hybrid coil, respectively.

T is a transmitter, P. B. OSC. are push-button dial oscillation circuits, each of which has one terminal connected to T1 and P1, which are shared connection terminals of windings N1 and N2.

ZN1 is a first balanced circuit, one terminal of which is connected to the shared connection terminal of windings N2 and N3 of the hybrid coil, and the other terminal C.

It is connected to one terminal of a DC blocking capacitor shown by and to R2, which is a shared connection terminal of the receiver R.

Capacitor C. The other terminal is connected to a terminal P3 which is electrically equal to the line terminal L2.

ZN2 is a second balanced circuit, one terminal of which is connected to R1, which is a terminal of winding N3, as well as one terminal of receiver R.

G1 and G2 are automatic level adjustment circuits for transmitting speech.

D1 and D2 are diodes provided according to the present invention, the anode of the diode D1 is connected to the terminal T2 together with one terminal of the transmitter T, the anode of the diode D2 is connected to one terminal of the second balanced circuit ZN2, and the diode The cathodes of D and D2 are both connected to terminal P2.

SW is a push button dial common switch, M, B
, C1 represent make, break, and common contacts, respectively.

Make contact M is push button dial oscillation circuit P. B. O
SC. The break contact B is connected to the P2 terminal, and the common contact C is connected to the P3 terminal.

The push-button-dial common switch SW may be a mechanical switch or an electrical switch, and operates in response to any of the 12 buttons (not shown) of the push-button-dial switch. It is.

The illustrated state of the common switch SW corresponds to a state in which the push button dial switch is not pressed, that is, a talking state.

In this state, contacts B and C of the common switch SW are connected, and contact M is disconnected.

When the pushbutton dial switch is pressed, that is, in the dial state, contacts M and C of the common switch SW are connected, and contact B is disconnected.

That is, when the pushbutton dial switch is pressed,
Push button dial oscillation circuit P. B. OSC. is terminal P
1 and P3, the transmitter T is opened, and when the push button dial switch is restored, the transmitter T is connected between the terminals P1 and P3 through the diode D1, and the push button dial oscillator circuit P. B. OSC. will be open.

In the talking state, terminal P2 is connected to P3, so the talking current flows to the transmitter T and the second balanced circuit ZN2, so the AC impedance of the diodes D1 and D2 is sufficiently small, and the DC voltage is balanced by the diodes D1 and D2. Therefore, the sidetone balance and the operation of the voltage detection type automatic level adjustment circuit for sending and receiving calls as shown in FIG. 1 are not affected, and the situation is equivalent to the talking state in FIG. 1.

The voice signal generated in the transmitter T induces signal voltages in the windings N1, N2, and N3 by the hybrid coil.

The first balancing circuit ZN cancels the signal voltage induced in the winding N3 and suppresses the sidetone that circulates from the transmitter T to the receiver R.

The second balancing circuit ZN2 is added to the first balancing circuit ZN1, and particularly improves low frequency sidetone compared to the case where only the first balancing circuit ZN1 is used.

Next, in the dial state, contacts M and C of the common switch SW are connected, while contacts B and C are disconnected, so terminal P
Push button dial oscillation circuit P.1 and P3. B. OS
C. is connected and sends a dial signal.

Terminal P2 is disconnected from P3 and diodes D1 and D2 are connected to the transmitter T and the second balanced circuit ZN2, respectively, and their cathodes are connected to each other, so the transmitter T and the second balanced circuit ZN2 receive direct current. There is no connection in terms of power or alternating current, and it is disconnected from the telephone circuit.

The dial signal generated between terminals P1 and P3 induces a signal voltage in the N1, N2, and N3 windings by the hybrid coil, and simultaneously sends the signal from the L, , and L2 terminals to the subscriber line, and is simultaneously This acts to cancel the induced voltage in the winding N3, and the difference is generated in the receiver R.

The signal generated at the handset R is a dial confirmation tone.

Although the dial confirmation sound is not shown, since the signal level generated in the handset R is conventionally reduced by another means during dialing, there is no effect even if the second balanced circuit ZN2 is disconnected from the circuit network.

Figure 2 shows the circuit configuration when the L1 terminal is positive and the L2 terminal is negative.
When the L2 terminal has positive polarity, the diodes D1 and D2 and the push button dial oscillation circuit P. B. OSC. By reversing the polarity of , the call and dial characteristics are equivalent to those of FIG.

As explained above, by connecting diodes to the transmitter and the second balanced circuit, and connecting the common connection terminal of each diode to the break contact of the common switch of the pushbutton dial, it is possible to connect the diodes to the transmitter and the second balanced circuit, and to connect the common connection terminal of each diode to the break contact of the common switch of the pushbutton dial. Similarly, the second balanced circuit improves low-frequency sidetone, and when dialing, the second balanced circuit, which has a large current bleed even in the shadow distance line, is disconnected to ensure stability of DC-like operation. By electrically separating the transmitter and the second balanced circuit by the two diodes, it is possible to prevent level fluctuations in the dial signal due to changes in the resistance of the transmitter.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional telephone circuit, and FIG. 2 is a circuit diagram showing an embodiment of the telephone circuit according to the present invention. L1, L2...Line terminal, L...Hybrid coil, T...Telephone, R...
・Handset, ZN1...First balance circuit, ZN2・
...Second balance circuit, co...Direct current blocking capacitor, P. B. OSC. ...Push button dial oscillation circuit, SW...Push button dial common switch, D1, D2...Diode, G
1... Transmission signal automatic level adjustment circuit, G2...
...Reception signal automatic level adjustment circuit.

Claims (1)

[Claims] 1 A booster type telephone circuit having a push-button dial, which is composed of a first winding, a second winding, and a third winding connected in series, and the first terminal of the first winding is connected to the first terminal of the line. a hybrid circuit connected to the hybrid coil, a transmitter and push button dial oscillation circuit whose first terminal is connected to the common connection terminal of the first winding and the second winding, and a second winding of the hybrid coil and the second winding of the hybrid coil; A first balanced circuit in which the first terminal is connected to the shared connection terminal of the third winding, a receiver and a second balanced circuit in which each of the first terminals is connected to the other terminal of the third winding of the hybrid coil. a DC blocking capacitor connected between a second terminal of the line and a shared connection terminal of a second terminal of the first balanced circuit and a second terminal of the handset; a first diode whose first terminal is connected to the second terminal of the second balanced circuit; and a second diode whose first terminal is connected to the second terminal of the second balanced circuit; a push-button dial common switch including a common contact connected to the second terminal of the break contact line connected to the shared connection terminal and a make contact connected to the second terminal of the push-button dial oscillation circuit; By operating the pushbutton dial common switch, the transmitter connected through the first diode and the second balanced circuit connected through the second diode are opened from the second terminal of the line, and at the same time, the first A telephone circuit characterized in that a transmitter and a second balanced circuit are electrically isolated by a diode and a second diode.