JPS61242450A - Power supply circuit of telephone set speech circuit - Google Patents

Abstract

PURPOSE:To eliminate decrease in characteristic impedance due to Early effect and the superposition of a ripple on the output of a constant voltage circuit and to facilitate the integration of the circuit by providing the constant voltage circuit connected between a constant voltage output terminal and a common terminal, an electronic switch connected between the connection point of a constant current circuit and a discharge preventing circuit and the common terminal, and a bias circuit which controls the opening and closure of the discharge preventing circuit. CONSTITUTION:The constant current circuit 21, discharge preventing circuit 23, and constant voltage circuit 24 are connected in series between the input terminal (P6) for power supply and signal input and output and the common terminal (P7), and the constant voltage output terminal (P8) is connected to the connection point of the discharge preventing circuit 23 and constant voltage circuit 24. Further, the electronic switch 22 which has the function of a comparison control circuit 25 is connected between the constant current circuit 21 and common terminal (P7). Further, the bias circuit 26 is connected between the constant current circuit 21 and discharge preventing circuit 23. Then, the characteristic impedance viewed from from the terminal is prevented from decreasing owing to the Early effect of the transistor of the constant current circuit 21 and the transistor of the discharge preventing circuit is prevented from operating as an opposite-directional transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power supply circuit for a telephone communication circuit that can be easily integrated into a semiconductor substrate.
・It is.

A simplified configuration of a prior art telephone is shown in FIG. In Fig. 4, 1 is the telephone office, 2 is the communication circuit, 3 to 5 are the lines, 6 is the diode bridge, (PL) (Pl) are the input/output terminals of the telephone, and (P, ) are the input terminals of the communication circuit 2. , (P,) are common terminals of the communication circuit 2. Telephone input/output terminal (p
z ) (p x ) is connected to the central office 1 through line 3 . Between the input and output terminals (Pl) (Pl) of the telephone, a direct current voltage and a receiving signal are sent from the telephone office 1 through the line 3, and a transmitting signal is sent from the telephone through the line 3, so that the direct current voltage and the voice signal are sent. A voltage with a superimposed signal is applied. Assuming that the audio signal is υL″sinωt,
A voltage in which an AC signal υL' sinωt is superimposed on a DC voltage VL' is applied between the input and output terminals (Pl), and an AC current i1. A current on which sinωt is superimposed flows. Terminals (P, ) (Pl) of communication circuit 2
In between is V, which is the voltage drop of the diode bridge 6.
L+υtsinωt is applied.

Figure 5 shows the DC characteristics required for a telephone.

The line current IL is 20+s depending on conditions such as line resistance.
It varies in the range of A to 100mA. - For example, according to Article 18 of Nippon Telegraph and Telephone Corporation Public Notice No. 149, the direct current resistance of a telephone is defined as 50Ω or more and 220Ω or less. This range is indicated by broken lines 7 and 8 in FIG.

Assuming that the voltage drop of the diode bridge 6 is 1.4V, the range of VL-IL allowed for the communication circuit 2 is shown by the solid line 9°10
This is the area surrounded by. Call circuit 2 that falls into this area
One conventional example of the DC characteristic VL-It is shown by a solid line 11.

Furthermore, according to Article 19 of Nippon Telegraph and Telephone Public Corporation Public Notice No. 149, the characteristic impedance of a telephone is defined as 600Ω. In order to realize this characteristic impedance, the characteristic impedance VL/it of 1 communication circuit 2 is set to 2, considering that other circuits are connected in parallel with 1 communication circuit 2.
It is desirable that the resistance is Ω or more.

Next, a voice transmission signal and DTMF (Dual Tone
It is necessary to satisfy υP≧3vpP and THD (distortion rate)≦3%, taking into consideration the transmission level of the MultiFrequency signal.

According to FIG. 5, when IL=20111A(7), OV<V
Although it is specified that L≦3v, it is desirable that vL be high in order to secure the above-mentioned vL sending level, and generally 1c I t, = 20 mA (7) When V L =
It is set at 2,7 V to 3 V. In the following, IL
=20111A(7) When Vt, :3V will be explained.

Generally, the electronic communication circuit 2 has V L = 3.
When the AC signal υLsinωt is superimposed on V, the DC current stops flowing at a certain instantaneous voltage, so the AC signal voltage is clipped and the waveform is distorted. In this way, the current IL
The voltage at which the current stops flowing is called the saturation voltage VL (sat). υL≧3Vpp, TI (To satisfy 063%, VL(sat) must be ≦1.5V. - The characteristics described so far are the characteristics that must be guaranteed for the power supply circuit in the communication circuit 2. , and are summarized below.

Condition ■ Number of DC resistance: When IL = 2011A (7), V t =
3 VI L= 100mA (7) when 3.6v≦V
L=20.6v condition ■Characteristic impedance: V+, /iL≦2 and Ω condition■ vL(sat)≦1.5V A conventional example that satisfies the above three conditions will be explained.

Nippon Telegraph and Telephone Public Corporation “Research and Practical Application Report” Volume 33 No. 6 P
A block diagram of a conventional communication circuit reported in No. 137 to P151 and 1988 Institute of Electronics and Communication Engineers General Conference No. 2265 is shown in FIG. 6, and an example of the circuit is shown in FIG. In FIG. 6, 12 is a constant current circuit, 13 is an electronic switch, 1
4 is a discharge prevention circuit, 15 is a constant voltage circuit, 16 is a comparison control circuit, and (P, ) is an output terminal. Furthermore, in Fig. 7, (Q,) to (Q,) are transistors, (zl) is a Zener diode, (C) is a capacitor, (
R) to (R3) are resistances. The constant current circuit 12 is set to have a DC characteristic VL-IL that satisfies the above condition (2), and the DC IL is supplied to the constant voltage circuit 15 through the discharge prevention circuit 14, and the DC voltage V is applied to the terminals (Ps) (Pl).
This DC voltage vO generated by o is generally Vo=1.
It is set to about 7V to 2V and is used as a voltage source for driving the communication circuit. The circuit for satisfying the above condition (2) is the electronic switch 13 and the comparison control circuit 16. Now, remove the electronic switch 13 from the circuit and connect the terminal (P 3 )
When a DC voltage vL is applied between (P 4 ) and the voltage value of this DC voltage vL is lowered, the voltage value of VL at which the DC current 2 stops flowing is defined as Vsat.

Vt, +υLsin (13t≧V,a), the electronic switch 13 is opened and the DC current IL is passed through the discharge circuit 14 and the constant voltage circuit 15 to the common terminal P4.

vL+υtsin (1) When t≧v g a t, the electronic switch 13 is closed and the DC current IL is passed through the electronic switch 13 to the common terminal P4. During this time, the output voltage Vo of the constant voltage circuit 15 is connected to the capacitor (C2).
Therefore, the predetermined voltage vO is maintained, and the operation of the 1-communication circuit 2 is maintained. In this way, the AC signal υ1. sin
Even when ωt is applied, it is kept constant, and the above condition (2) is realized.

Problems to be Solved by the Invention The first problem with the conventional configuration described above is a reduction in characteristic impedance due to the Early effect of the constant current source transistor (C2). In FIG. 7, when the electronic switch 13 is open, the emitter of the transistor (C2)
Since the AC voltage υL sin ωt is applied between the collectors, 11 sin ωt flows due to the Early effect. Generally, the collector current IC of the transistor (C2) is expressed by the following equation 0.

However, V(jE is the collector-emitter voltage, V^
is the early voltage, and Ico is the IC when V(!E=O, obtained by removing the I(!-VCE characteristic). From the above equation 0, the AC impedance between the collector and emitter of the transistor (C2) υt , /It is expressed by the following formula.

The characteristic impedance seen from the terminal (P3) (P, ) is 2
In order to make Ω or more, it is necessary that υL/i ≧ 2 and Ω. υL/11≧2, Ω, and ICO~Ia=
Substituting 100 mA into the above equation (2) gives the following equation 0.

V＾≧200■・・・・・・・・・■In other words,
Using the conventional circuit shown in Fig. 7, if you try to make the characteristic impedance seen from the terminal (P, ) (P4) more than 2Ω when IL=too■A, then the transistor (C2)
It is necessary that the early voltage of VA≧200V.

However, the early voltage of a PNP transistor in an integrated circuit is generally V = 50 to 100V, and in conventional circuits, the characteristic impedance seen from the terminal (P, ) (P4) is υ
Ill be unable to achieve Ω when L/i engineering≧2.

A second problem is that the discharge of the capacitor (C8) due to the reverse direction transistor of the PNP transistor (C4) cannot be ignored. The conventional circuit in Figure 7 has an IL of 20
FIG. 8 shows the voltage waveforms at each node when operating at 1OA, VL=3V, υL=3Vpp.

Although FIG. 8 shows a sawtooth wave for simplification, it is actually a sine wave. Solid lines 17 to 20 are vt, +
υLsin (11t, base voltage VBa of transistor (C3), collector voltage vC2 of transistor (C2), output voltage vO, and base voltage VB4 of transistor (C4). The saturation voltage is 0.2V, the base-emitter voltage in the active region is 0.7V, and the Raney diode (Z
The Zener voltage of 1) was set to 2V. The period of tl is V B
z > V B 4, and the constant current source transistor (
The current of C2) is supplied to the Raney diode (Zl) through the transistor (C4), and a predetermined voltage vO is output to the output terminal (P5). During the period t2, V B 3 >
V 84, and the collector current of the transistor (C2) is bypassed to the common terminal (P4) through the transistor (Q, ) to prevent clipping of the AC waveform at the input terminal (P3). However, period t in FIG. 8 is a period in which the emitter voltage of the transistor (C4) is lower than the collector voltage and the transistor (C4) operates as a reverse transistor. Therefore, the charge accumulated in the capacitor (C2) is rapidly transferred to both transistors (Q, ) (Q,
) is discharged to the common terminal (P4), causing the inconvenience that a ripple is added to the constant voltage circuit voltage vO.

The present invention solves the above-mentioned conventional problems, such as a reduction in characteristic impedance due to the Early effect.

It is an object of the present invention to provide a power supply circuit for a telephone communication circuit that does not cause ripples to be superimposed on the output of a constant voltage circuit and can be easily integrated into semiconductors.

Means for Solving the Problems In order to solve the above problems, the power supply circuit of the telephone communication circuit of the present invention has an input terminal for power supply and signal input/output, and a constant voltage output terminal for driving the circuit. , a common terminal,
a series circuit of a constant current circuit and a discharge prevention circuit connected between the input terminal and the constant voltage output terminal; a constant voltage circuit connected between the constant voltage output terminal and the common terminal; The configuration includes an electronic switch connected between a connection point between the current circuit and the discharge prevention circuit and the common terminal, and a bias circuit that controls opening and closing of the discharge prevention circuit.

Effects According to the above configuration, the bias circuit compares the voltage of the constant voltage output terminal and the voltage of the input terminal, and allows current to flow through the discharge prevention circuit during a period when the constant current circuit and the discharge prevention circuit are not saturated. During the saturation period, the discharge prevention circuit is controlled to be open. At this time, the voltage applied to the constant current circuit is made into direct current by transmitting the AC signal voltage of the input terminal to the constant current circuit through the discharge prevention circuit. This prevents the characteristic impedance seen from the terminal from decreasing due to the Early effect of the transistor in the constant current circuit, and at the same time prevents the transistor in the discharge prevention circuit from functioning as a reverse transistor.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3.

FIG. 1 is a circuit block diagram of a power supply circuit of a telephone communication circuit in an embodiment of the present invention, in which 21 is a constant current circuit, 22 is an electronic switch, 23 is a discharge prevention circuit, 24 is a constant voltage circuit, and 25 is a comparison control. circuit, 26 is a bias circuit, (R6)
is an input terminal, (R7) is a common terminal, and (R8) is a constant voltage output terminal. A constant current circuit 21 is connected between the input terminal (R6) and the common terminal (P, ) for power supply and signal input/output.
The discharge prevention circuit 23 and the constant voltage circuit 24 are connected in series, and a constant voltage output terminal (R8) is connected to the connection point between the discharge prevention circuit 23 and the constant voltage circuit 24. Furthermore, an electronic switch 22 having the function of a comparison control circuit 25 is connected between the constant current circuit 21 and the common terminal (R7). Further, a bias circuit 26 is connected between the constant current circuit 21 and the discharge prevention circuit 23.

Figure 2 is a circuit diagram of the above power supply circuit, (Q,) to (Q,
) is a transistor, (z2) is a Zener diode, (
D) is a diode, (C2) (C4) is a capacitor,
(R4) to (R8) are resistors, and (D) is a constant current source. Common base coupling pair PNP )-ransistor (Q,
) (Q6) and connect them to the input terminal (R6).
and the base and collector of the PNP transistor (Q,) are connected in common, and the series resistors (R4) (R1)
is connected between the PNP transistor (Q,) and the common terminal (R7), and a capacitor (
C1) is connected to constitute a constant current circuit 21.

In addition, the base is connected to a resistor (R4) (RS
) is connected to the emitter-collector of a PNP transistor (Q7) to form an electronic switch 22. In addition, the emitter of the PNP transistor (Q,) is connected to the collector of the PNP transistor (Q6), and the collector of the transistor (Q,) is connected to a reversely connected Zener diode (z2) and a capacitor (C4).
A discharge prevention circuit 23 and a constant voltage circuit 24 are respectively connected to the parallel circuit. Note that the comparison control circuit 25 is shared by the electronic switch 22.

Furthermore, the collector of the NPN transistor (Q,) is connected to the input terminal (R6), and the base is connected to the constant voltage output terminal (P
) and the common terminal (R7).
s) (Rff) and connect a forward diode (Dl) between the input terminal (P, ) and the common terminal (R7).
Connect the resistor (R8) and constant current power supply (Engineer) in series,
The emitter of a PNP transistor (Q9) is connected between the resistor (Ro) and the constant current power supply (Engine) to constitute the bias circuit 26, and the emitter is connected to the PNP transistor (Q9) that constitutes the discharge prevention circuit 23. It also has a common connection to the base.

The 21st ffl(7) circuit is defined as Vt, = 3 V, υ
FIG. 3 shows the voltage waveforms at the main nodes when operating at L=3 Vpp. In FIG. 3, a sawtooth wave is used to simplify the drawing, but it is actually a sine wave. NPN
The transistor (Q9) and a constant current string (Eng.,) form an emitter follower, and the base of the NPN transistor (Q,) is a voltage obtained by dividing the constant voltage Vo by the resistor (R,) (R,). Biased. If such a circuit configuration is adopted, the emitter potential of the NPN transistor (Q,) is determined by the base DC current even if the emitter is swung by the AC voltage υ(, sinωt) through the diode (Dl) and resistor (R6). The voltage does not fall below the potential of the discharge prevention circuit 23, and the waveform is clipped.This waveform is shown by the solid line 27 in FIG. The current of the constant current circuit 21 is supplied to the constant voltage circuit 24, and the voltage V is applied to the constant voltage output terminal (P,).

is output. On the other hand, during period t, the electronic switch 22 is closed and the current is bypassed to the common terminal (R7) of the constant current circuit 21. During this period t3, a predetermined voltage Vo is maintained by the capacitor (C4). During period t3, PN
The waveform of the base voltage of the P transistor (Q7) is also during periods t, yt, and t4.

The waveforms of the base voltages of the PNP transistors (Q,) are respectively transmitted to the collectors of the PNP transistors (Q6), and the waveforms become the waveforms shown by solid lines 28. From this, the emitter-collector voltage of the PNP transistor (Q6) becomes close to direct current, and the PNP transistor (
The early effect of Q6) can now be ignored. During the period t2, some ripples occur between the emitter and collector of the PNP transistor (Q6), but experience has shown that there is no practical problem. In addition, solid line 2 in Figure 3
9 is VL 10υ1. This is the waveform of sinωt.

Effects of the Invention As described above, according to the present invention, it is possible to easily obtain a power supply circuit for a telephone communication circuit that has a characteristic impedance of 2Ω or more and less ripple in the constant voltage output vO, with a small increase in the number of elements. .

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of a power supply circuit of a telephone communication circuit in one embodiment of the present invention, FIG. 2 is a circuit diagram of the same power supply circuit, FIG. 3 is a voltage waveform diagram of each part of the circuit shown in FIG. Figure 4 is a schematic configuration diagram of a telephone, Figure 5 is an explanatory diagram of the DC characteristics that must be satisfied by the telephone and its communication circuit, Figure 6 is a circuit block diagram of a conventional power supply circuit, and Figure 7 is a circuit diagram of the same power supply circuit. ,
FIG. 8 is a voltage waveform diagram of each part of the circuit shown in FIG. 7. 21... Constant current circuit, 22... Electronic switch, 23
...Discharge prevention circuit, 24... Constant voltage circuit, 26...
・Bias circuit, (P,)...input terminal, (R7)・
...Common terminal, (P,)...Constant voltage output terminal, (Q
5)~(Q9)...Transistor, (Dl)...Diode, (D)...Constant current source, (R4)~(R8
)...Resistor, (C3) (C4)...Capacitor,
(Z2)...Zener diode agent Yoshihiro Morimoto Figure 1 r6 --- Input ring) Py-Ichiro-dori j'1i) h゛-" Constant voltage output terminal Figure J Figure 7 , 12 Figure 3 VCV)

Claims (1)

[Claims] 1. An input terminal for power supply and signal input/output, a constant voltage output terminal for driving a circuit, a common terminal, and an input terminal connected between the input terminal and the constant voltage output terminal. a series circuit of a constant current circuit and a discharge prevention circuit, a constant voltage circuit connected between the constant voltage output terminal and the common terminal, a connection point between the constant current circuit and the discharge prevention circuit, and the common terminal. A power supply circuit for a telephone communication circuit, comprising an electronic switch connected between the discharge prevention circuit and a bias circuit for controlling opening and closing of the discharge prevention circuit. 2. The bias circuit includes a series circuit of a forward diode, a first resistor, and a constant current source connected between the input terminal and the common terminal, and a constant voltage output terminal and the common terminal. a series circuit of a second resistor and a third resistor, the collector of which is connected to the input terminal, the emitter of which is connected to the connection point of the first resistor and the constant current source, and the base of which is connected to the second resistor; and a first NPN transistor connected to a connection point between the input terminal and the third resistor, and the constant current circuit includes second and third PNP transistors whose emitters are both connected to the input terminal.
The discharge prevention circuit has a base connected to the emitter of the first transistor, a collector connected to a constant voltage circuit, and an emitter connected to the collector of one of the second and third transistors. 2. A power supply circuit for a telephone communication circuit according to claim 1, wherein the power supply circuit includes a PNP type fourth transistor.