JPH056946B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] First and second constant current sources are operated alternately in response to a signal from a reference signal source, and a ringing signal consisting of a constant current in positive and negative directions is sent to the telephone. Since it does not require a transformer or the like, it can be made smaller.

[Industrial application field]

The present invention relates to a calling signal sending circuit for sending out a calling signal to a subscriber telephone.

The ringing signal that rings the bell of the subscriber's telephone to notify the user of an incoming call is sent out from the ringing signal sending circuit at a frequency of 16Hz or 20Hz and as an AC voltage with an effective value of about 75V at a predetermined intermittent ratio. It is desired to reduce the weight and size of such a calling signal sending circuit, thereby reducing the size of the switching equipment.

[Conventional technology]

The subscriber circuit has a so-called BORSCHT function, where B is battery feed, O is overvoltage protection, R is ringing, S is line supervision, and C is is code decoding (Codec), H is 2-wire to 4-wire conversion (Hybrid), T is testing (Testing)
It is.

FIG. 7 is an explanatory diagram of a conventional example, where 31 is a network of digital exchanges, 32 is a subscriber circuit,
33 is a subscriber telephone, 34 is the aforementioned BORSCHT
Of the functions, B (power supply), S (line monitoring), H (2
35 is a calling signal oscillator, 36 is a DC power supply,
R10 and R11 are current-limiting resistors, rl is a contact for a relay (not shown), and TIP and RING are terminals. Note that the O (overvoltage protection) function, which is not included in the circuit 34 of the BSHC function, is configured by distributed-connected varistors, etc., and the T (test) function is a connection configuration with the test equipment, and is directly connected to the calling signal transmission. There is no such relationship. Further, the R (calling signal sending) function is realized by a calling signal oscillator 35, a relay contact rl, etc., and is provided closer to the subscriber line than the BSHC function circuit 34. Further, the calling signal oscillator 35 and the DC power supply 36 are shared by a plurality of subscriber circuits.

When the contact rl of the relay (not shown) is in the state shown, the ringing signal from the ringing signal oscillator 35 passes through the bell circuit of the telephone 33 via the resistor R10 and the contact rl, and then via the contact rl and the resistor R11. Flows into the earth.
Further, a DC voltage from a DC power supply 36 is superimposed on the ringing signal oscillator 35, and when the telephone 33 is taken off-hook in response to the ringing signal, a DC current flows from the DC power supply 36, so that off-hook detection can be performed using this DC current. can. Then, a relay (not shown) is operated by off-hook detection,
The contact rl is switched and connected to stop sending out the calling signal, and at the same time, the telephone 33 is connected to the network 31 via the circuit 34. At this time, the DC current from the DC power supply 36 is limited by the sum of the resistors R10 and R11 and the subscriber resistance.

In addition, as shown in the figure, the DC power supply 36 may be provided on the resistor R10 side (on the calling signal oscillator 35 side), or
It may be provided on the resistor R11 side, and is selected depending on the system configuration.

Conventionally, a configuration shown in FIG. 8 or 9 has been used to superimpose a ringing signal and a DC voltage and send the superimposed signal to a subscriber's telephone. In FIG. 8, a signal with a frequency of, for example, 16 Hz from an oscillator 43 is amplified by an amplifier 42 and supplied to the primary winding of a transformer 41 with a turns ratio of 1:n, and an effective value of 75 V is applied to the secondary winding.
This voltage is applied to the DC power supply 44.
DC voltage is superimposed and sent to the subscriber's telephone via contact RL. In this case, the transformer 41 boosts the low frequency signal and has a direct current flowing therethrough, so it becomes large.

In FIG. 9, in order to reduce the size of the transformer 41 in FIG. 8, a center tap is provided in the primary winding of the transformer 51, and current is alternately passed through the windings on both sides of the center tap. For example, a 16 Hz signal from 56 is applied to the bases of transistors 52 and 53 via a non-inverting driver 54 and an inverting driver 55, and is alternately controlled to turn on and off, and is connected to the center tap of the primary winding with a turns ratio of 1:n. A current is supplied from a power supply 57, and a DC voltage from a DC power supply 58 is superimposed on the voltage induced in the secondary winding, and the superimposed voltage is sent to the subscriber telephone via a contact rl.

[Problem that the invention seeks to solve]

The conventional calling signal sending circuit includes a transformer 41,
51, and this transformer 41, 51
The transformer boosts a low frequency signal of about 16 Hz to 25 Hz, and the lower the frequency, the larger the transformer becomes, so the transformers 41 and 51 for sending the calling signal also become larger. Furthermore, since DC superposition is performed to detect off-hook of subscriber telephones, DC current flows through the transformers 41 and 51, and the cores of the transformers 41 and 51 are prevented from being magnetically saturated by this DC current. Since it is necessary to do this, the core becomes large. From this point of view as well, the transformers 41 and 51 for transmitting the calling signal have the disadvantage of being heavy and large.

Furthermore, since the conventional calling signal sending circuit corresponds to a constant voltage source, the current control resistor R10,
R11 is required. These resistors R10, R11 are
In consideration of the heat generated by the current flowing when the telephone is off-hook and the heat generated by the current caused by ground faults in the subscriber line, a large resistor of several watts is used, and therefore the mounting area is small. The disadvantage was that it became larger.

In addition, there is a tendency for switching equipment to distribute functions and load distribution, but as mentioned above, the size of the ring signal sending circuit increases, so it is common to install one to several circuits in common throughout the entire switching equipment. It was hot. Therefore, 1~
It was difficult to construct a more reliable system by installing a calling signal sending circuit for every several dozen lines and distributing the calling signal sending function.

An object of the present invention is to reduce the size and weight, and to easily accommodate functional distribution.

[Means for solving problems]

The calling signal sending circuit of the present invention uses the sum of currents of the first and second constant current sources as the calling signal,
This will be explained below with reference to FIG.

A first constant current source 1 that draws in current, a second constant current source 2 that sends out current, and the first and second constant current sources 1 and 2 alternate in response to the signal from the reference signal source 3. and a control circuit 4 for causing the subscriber telephone 5 to send out a calling signal. This control circuit 4 is shown as being composed of an inverting driver 6 and a non-inverting driver 7. Further, the first constant current source 1 and the second constant current source 2 are constituted by a current mirror circuit, and the first constant current source 1 is connected to the power supply V _SS
The second constant current source 2 is connected to the power supply _VDD , and the connection point between the first and second constant current sources 1 and 2 is connected to the subscriber telephone 5 via a contact RL. .
Reference numeral 8 indicates a circuit for the BSCH function, and the telephone 5 is connected to the exchange network via this circuit 8.

[Effect]

The control circuit 4 operates the constant current sources 1 and 2 alternately depending on the positive or negative polarity of the signal from the signal source 3. For example, when the signal from the signal source 3 has negative polarity, the first constant current source The current source 1 is operated to draw current by the power supply V _SS , and when the signal from the signal source 3 is positive, the second constant current source 2 is operated and the power supply is
V _DD causes the current to be sent out, and the telephone set 5 is alternately supplied with the set currents from the first and second constant current sources 1 and 2. Therefore, AC calling The bell rings because there is a signal.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of the main part of an embodiment of the present invention, which uses a current mirror circuit. This current mirror circuit has the function of supplying an output current proportional to the input current. If it is constant, the output current will also be constant in proportion to it, so a constant current circuit can be constructed. Hereinafter, in the present invention, a configuration consisting of a current mirror circuit that supplies an output current proportional to an input current will be referred to as a constant current source or a constant current circuit. This is an embodiment in which this current mirror circuit is used as the first and second constant current sources.
2 is a current mirror circuit (M0, M1) constituting the first and second constant current sources; 13 is a signal source; 14 is a control circuit; 15 is a telephone; 16 is an inverting driver;
Reference numeral 17 denotes a non-inverting driver, and for the sake of simplicity, a case is shown in which the terminal TIP is grounded and the contact rl is connected to the terminal RING.

A signal having the frequency of the calling signal is output from the signal source 13, and when the signal has negative polarity, the inverting driver 16
A current I ₁ is supplied from the current mirror circuit 11 as an input current. The current mirror circuit 11 is
A current I ₅ proportional to this current I ₁ is drawn. Further, when the signal from the signal source 13 is of positive polarity, the non-inverting driver 17 draws current I ₀ from the current mirror circuit 12 as an input current, and the current mirror circuit 12
delivers a current I ₄ proportional to this current I ₀ . Therefore, currents I ₅ and I ₄ of constant current value and alternately opposite directions are supplied to the telephone 15 via the contact rl. That is, an alternating current calling signal is supplied via the contact rl, and the bell of the telephone 15 rings.

The output voltage Vout corresponds to the impedance of the telephone 15 and the subscriber line, but the current supplied from the current mirror circuits 11 and 12 is
Since it is constant regardless of this output voltage Vout,
The current mirror circuits 11 and 12 can be regarded as high impedance constant current sources. Also, the output voltage Vout never exceeds the power supply voltages V _SS and V _DD .

Furthermore, in the case of a ground fault in a subscriber line, due to the characteristics of the constant current circuit, a current exceeding a certain level will not flow, so there is no need to provide a resistor to limit the short circuit current.

FIG. 3 is a circuit diagram of a main part of an embodiment of the present invention, and the same reference numerals as in FIG. 2 indicate the same parts. The first current mirror circuit 11 includes a transistor Q3,
The base of transistors Q3 and Q5 is connected to the input side transistor Q3.
connected to the collector. The second current mirror circuit 12 is composed of transistors Q2, Q4, and resistors R2, R4.
The base of Q4 is connected to the collector of transistor Q2 on the input side. Note that the current mirror circuit generally has a configuration using a pair of transistors as described above, but various configurations can be adopted.

The control circuit 14 is composed of an operational amplifier OPA, transistors Q0 and Q1, and a resistor R0. The signal source 13 is connected to the non-inverting input terminal (+) of the operational amplifier OPA, and the transistors Q0 and Q0 are connected to the output terminal.
The base of Q1 is connected to those transistors
The emitters of Q0 and Q1 are connected to the inverting input terminal (-) of the operational amplifier OPA, and to the resistor R0.

Assuming that the base-emitter voltages of transistors Q3 and Q5 are equal, and that the current amplification factor h _FE is sufficiently large, the input current of the current mirror circuit 11 is
The relationship between I ₁ and the output current I ₅ is R3·I ₁ =R5·I ₅ ...(1), so I ₅ =(R3/R5)·I ₁ ...(2). Therefore, when R3>R5, the output current _I5 can be controlled with a small input current _I1 .

Similarly, in the current mirror circuit 12, the following relationship holds: I ₄ =(R2/R4)·I ₀ (3).

The operational amplifier OPA has a signal voltage Vs applied to the non-inverting input terminal (+) and an inverting input terminal (-).
The emitter potential of transistors Q0 and Q1 is equal to the signal voltage.
It will be the same as Vs. Assuming that the current amplification factor h _FE of transistors Q0 and Q1 is sufficiently large, the current I ₀ flowing through transistor Q0 when the signal voltage Vs is positive is I ₀ =Vs/R0 (4), but, The current I ₁ flowing through transistor Q1 is 0
becomes. Also, when the signal voltage V _S has negative polarity, the current I ₁ flowing through the transistor Q1 is I ₁ = -Vs/R0 (5), but the current I ₀ flowing through the transistor Q0 is 0.
becomes.

Note that the signal voltage Vs is selected so as to be equal to or lower than the reverse breakdown voltage between the bases and emitters of the transistors Q0 and Q1.

Currents I ₁ and I ₀ that flow depending on the polarity of the signal voltage Vs
Accordingly, the sum of the currents I ₅ and I ₄ multiplied by R3/R5 and R2/R4 from the current mirror circuits 11 and 12, respectively, is sent to the telephone set 1 as the ringing signal current Iout via the contact rl.
Sent on 5th.

If the load impedance including the impedance of the telephone 15 is _ZL , the output voltage Vout is Vout=Iout· _ZL (6). However, this output voltage Vout never exceeds the power supply voltages V _DD and V _SS . Also, if the telephone 15 goes off-hook in response to a ringing signal, its impedance becomes almost zero, so the output voltage
Vout decreases. Therefore, off-hook can be detected by detecting this output voltage Vout. In other words, even without performing DC superposition,
Off-hook detection becomes possible. In addition, the power supply voltage
If V _DD and V _SS are set to, for example, +75V and -75V, the output voltage Vout will be a call signal with an amplitude of ±75V centered around 0V, but for example, V _DD = +27V, V _SS
If it is set to = -123V, the ringing signal will have an amplitude centered around -48V, making it possible to send out a ringing signal that looks like a superimposed direct current.

FIG. 4 is an explanatory diagram of the operation, in which a indicates the voltage Vs signal from the signal source 13, and this signal causes b,
As shown in c, current I ₀ is applied to transistors Q0 and Q1,
I ₁ flows. Since these currents I ₀ and I ₁ become the input currents of the current mirror circuit, the calling signal current Iout is
It will be as shown in d.

Further, the output voltage Vout is as shown in e. Also, when the load impedance Z _L is large, the output voltage Vout tends to increase as shown by the dotted line of f, but
The output voltage cannot increase above the power supply voltages V _DD and V _SS . In this state, the transistors Q5 and Q4 on the output side of the current mirror circuits 11 and 12 are saturated, and the resistors R5 and R4 are also set to low values, so they are connected to the power supply with low impedance, and the solid line The output voltage as shown in
Vout will be clamped within the power supply voltages V _DD and V _SS .

FIG. 5 is a circuit diagram of a main part of another embodiment of the present invention, and the same reference numerals as in FIG. 3 indicate the same parts. In this embodiment, the transistor on the input side of the current mirror circuit is omitted to simplify the circuit.The current mirror circuit 11 is composed of a transistor Q5 and resistors R13 and R15, and the current mirror circuit 12 is composed of a transistor Q5 and resistors R13 and R15. , transistor Q4, and resistors R12 and R14.

The currents I ₅ and I ₄ flowing through the output side transistors Q5 and Q4 due to the power supply voltages -V and +V increase the base-emitter voltage of the output side transistors Q5 and Q4.
Assuming V _BE5 and V _BE4 , I ₅ = (I ₁ · R13 − V _BE5 ) / R15 ... (7) I ₄ = (I ₀ · R12 − V _BE4 ) / R14 ... (8). However, it is assumed that the current amplification factor h _FE of the transistor is sufficiently large. Compared to the current mirror circuit in the embodiment shown in FIG. 3, the error caused by the base-emitter voltages V _BE5 and V _BE4 is small, and the transistor on the input side can be omitted, resulting in an economical configuration. It is possible to obtain practically sufficient characteristics.

Further, this embodiment shows a case where the signal from the signal source 13 is a logic level pulse signal, and the control circuit 14 is configured accordingly. That is, operational amplifier OPA1, transistors Q0 and Q1, and resistor R10,
It consists of R16, R17, RB1, RB2 and capacitor C1.

The voltage V _CC is divided by resistors RB1 and RB2 and applied to the non-inverting input terminal (+) of operational amplifier OPA1, and the signal from signal source 13 is applied to the inverting input terminal (-) of operational amplifier OPA1 via resistor R16. . Assuming that the signal from this signal source 13 is a pulse signal with a calling signal period consisting of potentials between 0 and V _CC , the resistance
RB1/RB2=3/1, and resistors R16 and R17
When R16=R17, the voltage generated across resistor R10 has an amplitude of ±V _CC /2. Therefore, this voltage allows currents I ₀ and I ₁ to flow through transistors Q0 and Q1, so the call signal current Iout, which is the sum of currents I ₅ and I ₄ from current mirror circuits 11 and 12, is applied to contact rl.
can be sent to the telephone 15 via.

Also, the input signal voltage is a rectangular wave, but the capacitor
C1 and resistors R16 and R17 constitute a kind of integration circuit, and the voltage generated across resistor R10 has a waveform that is blunted, making it possible to make the calling signal current waveform closer to a sine wave.

FIG. 6 is an explanatory diagram of the operation, and a indicates a signal from the signal source 13, which is a pulse signal consisting of potentials between 0 and V _CC . This signal is applied to the inverting input terminal (-) of operational amplifier OPA1 via resistor R16,
Since voltage V _CC is divided by resistors RB1 and RB2 and applied to the non-inverting input terminal (+) of operational amplifier OPA1, in operational amplifier OPA1, V _CC /4
By applying _an output signal corresponding to the difference _between .

Currents I ₀ and I ₁ corresponding to this voltage flow through the transistors Q0 and Q1 as shown in c and d, and similarly to the previous embodiment, these currents I ₀ and I ₁ become input currents and become current mirrors. Current I ₅ from circuits 11 and 12,
I ₄ is output, and the sum of the ringing signal current Iout is the contact
sent to the telephone 15 via rl, the output voltage
Vout is as shown in e and f. f indicates a case where the load impedance is large, and even if the output voltage Vout attempts to increase as shown by the dotted line, it will be clamped to the power supply voltages +V and -V.

The present invention is not limited to the above-described embodiments, but can be modified in various ways.

〔Effect of the invention〕

As explained above, the present invention transmits a calling signal by alternately operating the first and second constant current sources 1 and 2, and there is no need to use a transformer as in the conventional example. It has the advantage of being smaller and lighter. Furthermore, since constant current sources 1 and 2 are used, a current exceeding the set current will not flow during off-hook or ground faults, improving safety and eliminating the need for current-limiting resistors. Therefore, it can be made smaller and more economical.

Furthermore, since it is easy to integrate the system into an integrated circuit, it is possible to provide a calling signal sending circuit for each subscriber circuit, thereby distributing the functions and contributing to improving the reliability of the system.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is a block diagram of the main part of an embodiment of the invention, Fig. 3 is a circuit diagram of the main part of an embodiment of the invention, and Fig. 4 is a diagram of the main part of an embodiment of the invention. An explanatory diagram of the operation of one embodiment, FIG. 5 is a main circuit diagram of another embodiment of the present invention, FIG. 6 is an explanatory diagram of the operation of another embodiment of the present invention, and FIG. 7 is an explanatory diagram of the conventional example. , FIG. 8, and FIG. 9 are explanatory views of the main parts of the conventional example. 1 and 2 are constant current sources, 3 is a signal source, 4 is a control circuit diagram, 5 is a telephone, 6 is an inverting driver, 7 is a non-inverting driver, 8 is a BSCH circuit, RL is a relay contact,
11 and 12 are current mirror circuits (M0, M1),
13 is a signal source, 14 is a control circuit, 15 is a telephone,
16 is an inverting driver, and 17 is a non-inverting driver.

Claims (1)

[Scope of Claims] 1. In a calling signal sending circuit that sends a calling signal to a subscriber's telephone, a first constant current source 1 consisting of a current mirror circuit that draws a current proportional to the input current; The first constant current source is controlled by a second constant current source 2 consisting of a current mirror circuit that sends out a proportional current, a ringing signal period and a signal from the reference signal source 3, and a signal obtained by inverting the signal. 1 and a current sending operation by the second constant current source 2 alternately to send out a calling signal to the subscriber telephone. Signal sending circuit. 2. The reference signal source 3 is configured to output a pulse signal having a calling signal period, and the control circuit 4 includes an operational amplifier that inputs the pulse signal, and an integrating circuit that approximates the output signal waveform of the operational amplifier to a sine wave. and a transistor that alternately supplies the input current of the first constant current source 1 and the input current of the second constant current source 2 according to the output signal of the operational amplifier. A calling signal sending circuit according to claim 1.