JP2994844B2 - Transmission input / output circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a transmission terminal device connected to a transmission line such as a telephone line, for example, for transmitting a transmission signal of a DTMF dialer or an FSK modem to the transmission line or for transmitting a signal from the transmission line. The present invention relates to a transmission input / output circuit for receiving a transmission signal.

[0002]

2. Description of the Related Art As shown in FIG. 5, this type of transmission input / output circuit has terminals T1 and T2 connected to a transmission line such as a telephone line, and a signal received from the transmission line via the terminals. Is connected to a receiving circuit 3 having, for example, a DTMF receiver or an FSK demodulator, and a transmitting circuit 2 having a DTMF dialer or an FSK modulator.
The analog transmission signal from the transmission circuit 2 is processed, and a terminal T
The transmission is made to the transmission line via 1 and 2.

Although such a transmission input / output circuit is conventionally formed using a transformer or using an operational amplifier, the power consumption is reduced as much as possible, and the transmission input / output circuit is inexpensive and small. At the same time, it is important that the input and output AC impedances are constant and noise components other than the required transmission signal are not output.

[0004]

In the conventional transmission input / output circuit configured as described above, when a transmission signal is output, the transmission circuit 2 such as a DTMF dialer or an FSK modulator is activated from a power down state. Then, since the output signal of the transmission circuit 2 changes rapidly, the change in the signal is output as a noise signal, which causes a problem that the device malfunctions.

In the conventional transmission input / output circuit, the "unnecessary transmission level" in the technical standards is
That is, there is a problem that it is difficult to remove unnecessary noise components from the fundamental wave of the transmission analog waveform.

Furthermore, it is difficult to reduce the size and the price of a conventional transmission input / output circuit using a transformer, the power consumption of the amplifier and operational amplifier used therein is large, and furthermore, it meets the technical standards. Does not have enough amplitude, 5V or 3
There is also a problem that the operation cannot be performed with the power supply voltage of V.

[0007] The present invention has been made in view of the above,
It is an object of the present invention to provide a transmission input / output circuit which prevents output of noise generated when the transmission circuit is started from a power-down state, and achieves miniaturization and low cost. It is another object of the present invention to provide a transmission input / output circuit that eliminates unnecessary noise components due to the influence of power supply ripples and achieves miniaturization and low cost.

[0008]

In order to achieve the above object, a transmission input / output circuit of the present invention is a transmission input / output circuit connected to a transmission terminal device for transmitting and receiving a transmission signal to and from a transmission line, An operational amplifier for supplying an analog transmission signal to be transmitted to a transmission line to a non-inverting input terminal and amplifying the transmission signal, and an output side of the operational amplifier for outputting an AC component of an output signal of the operation amplifier to the transmission line. , A resistor connected at one end to the transmission line to determine an AC input / output impedance to the transmission line, and an on-resistance for varying the line impedance of the transmission line. Is connected between the other end and the AC coupling means, and constitutes a resistance voltage dividing circuit based on the impedance of the transmission line, the resistance means and the on-resistance. A variable resistance means for changing the on-resistance, transmitting a transmission signal to the transmission line by the change of the on-resistance, determining a reception AC impedance at the time of reception, and forming a constant AC input / output impedance at the time of transmission and reception; One end is connected between the variable means and the resistance means, the other end is connected to the input of the operational amplifier, AC amount feedback means for feeding back an AC amount to the operational amplifier, and an output and an inverted input of the operational amplifier. A DC amount feedback unit connected between the AC coupling unit and the resistance variable unit, and connected between the AC coupling unit and the resistance variable unit. Is supplied to the variable resistance means, the on-resistance of the resistance variable means drops below a predetermined value, and is transmitted to the transmission line as noise. And control means for controlling to inhibit Rukoto, and summarized in that and a receiving means for extracting the alternating current received signal from the transmission line.

The transmission input / output circuit of the present invention is a transmission input / output circuit connected to a transmission terminal device for transmitting / receiving a transmission signal to / from a transmission line. An operational amplifier that is supplied to an inverting input terminal and amplifies the transmission signal; AC coupling means connected to an output side of the operational amplifier to output an AC component of an output signal of the operational amplifier to a transmission line; Between the other end of the resistance means and the AC coupling means so as to have an on-resistance that has one end connected to the transmission line to determine the AC input / output impedance with respect to To form a resistance voltage dividing circuit based on the impedance of the transmission line, the resistance means and the on-resistance. A transmission signal is transmitted to the transmission line by the change, a reception AC impedance is determined at the time of reception, and a variable resistance means for forming a constant AC input / output impedance at the time of transmission and reception, and one end is provided between the variable resistance means and the resistance means. The other end is connected to the input of the operational amplifier, AC amount feedback means for feeding back an AC amount to the operational amplifier, and connected between the output of the operational amplifier and an inverting input terminal, the operational amplifier DC amount feedback means for feeding back the DC amount of the output signal of the operational amplifier to the operational amplifier; and a non-inverting portion of the operational amplifier to which the transmission signal is supplied to remove unnecessary noise components supplied to a non-inverting input terminal of the operational amplifier. A first filter means connected to the inverting input terminal, and an unnecessary noise component provided in the ac amount feedback means. There a second filter means for preventing from being supplied to said operational amplifier,
A gist of the present invention is to have a receiving means for taking out a received signal from the transmission line in an alternating manner.

[0010]

According to the transmission input / output circuit of the present invention, the control means including, for example, a zener diode connected between the AC coupling means and the variable resistance means reduces noise of a predetermined voltage or more supplied to the variable resistance means. As a result, the on-resistance of the variable resistance means is reduced to a predetermined value or less, thereby preventing noise from being transmitted to the transmission line.

In the transmission input / output circuit of the present invention, the first filter means is connected to the non-inverting input terminal of the operational amplifier to which the transmission signal is supplied, and the second filter means is provided in the AC amount feedback means. This prevents unnecessary noise components from being supplied to the operational amplifier.

[0012]

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

FIG. 1 is a circuit diagram of a transmission input / output circuit according to one embodiment of the present invention. The transmission input / output circuit shown in the figure has terminals T1 and T2 to which a transmission line such as a telephone line is connected, and a reception circuit 3 is connected from a terminal T2 via a capacitor C1 and sends out to the transmission line. A transmission circuit 2 such as a DTMF dialer or an FSK modulator for generating an analog transmission signal to be output is connected, and a signal injection circuit 1 and a signal injection circuit 1 to which a transmission signal from the transmission circuit 2 is supplied.
And a resistor R1 connected between the transmission line and the terminal T2 and determining the AC input / output impedance for the transmission line. The signal injection circuit 1 amplifies the transmission signal from the transmission circuit 2 and, together with the resistor R1, determines the AC input / output impedance during reception. When the transmission line is, for example, a telephone line, the resistance R1 is desirably 600Ω matched to the impedance of the telephone line. Also,
The receiving circuit 3 includes an FSK demodulator, a DTMF receiver, and the like.

The signal injection circuit 1 has an operational amplifier OP1 for supplying a transmission signal to be transmitted from the transmission circuit 2 to a non-inverting input terminal via a resistor R4 and a capacitor C5, and amplifying the transmission signal. The non-inverting input terminal of the operational amplifier OP1 is connected to a connection point of resistors R8 and R9 connected in series between the power supply voltage and the ground, and is supplied with a DC bias voltage. Further, a feedback resistor R2 is connected between the output of the operational amplifier OP1 and the inverting input terminal, and the inverting input terminal is connected to the ground via the capacitor C3, whereby the output signal of the operational amplifier OP1 is connected to the resistor R2. And the capacitor C3, and only the DC component is supplied to the inverting input terminal of the operational amplifier OP1 to be set in a balanced state.

Further, only the AC component of the output signal of the operational amplifier OP1 is taken out via the capacitor C2 and supplied to the base of the transistor Tr1. Transistor T
The base of r1 is connected to the connection point of the resistors R6 and R7 connected in series between the power supply voltage and the ground, and is supplied with a DC bias voltage and is connected to the cathode of a Zener diode ZD1 having a predetermined Zener voltage. The anode of the Zener diode ZD1 is connected to the ground. The emitter of the transistor Tr1 is connected to the ground via the resistor R5, and the resistors R5, R6, R7
By appropriately selecting the resistance value of the transistor Tr
One bias point is determined.

The Zener diode ZD1 is provided so that the voltage supplied to the base of the transistor Tr1 does not exceed the Zener voltage of the Zener diode ZD1.

The connection point between the collector of the transistor Tr1 and the resistor R1 is connected to a resistor R3 and a capacitor C4.
To the non-inverting input terminal of the operational amplifier OP1 and appear at the collector of the transistor Tr1.
An AC component of the transmission signal transmitted to the transmission line via the resistor R1 is connected to the operational amplifier OP via the resistor R3 and the capacitor C4.
1 is fed back to the non-inverting input terminal of the transistor Tr1.
The inversion forms a negative feedback loop, and the system is balanced. The AC amplification factor is determined by the ratio of the sum of the impedances of the resistor R4 and the capacitor C5 and the ratio of the sum of the impedances of the resistor R3 and the capacitor C4. Also,
The DC bias point at the connection point between the transistor Tr1 and the resistor R1 is determined by the amplification factor h _fe of the transistor Tr1, the resistances R5 and R
6, R7, and the sum of the transmission line impedances.

The transistor Tr1 changes the line impedance of the transmission line, and includes a collector-emitter resistance, a resistance R5, and a resistance R of the transistor Tr1.
1. The impedance of the transmission line, that is, the telephone line, constitutes a voltage divider circuit, which generates a voltage on the collector side of the transistor Tr1.

In the transmission input / output circuit configured as described above, in order to output a transmission signal, an FSK modulator or a DSK
When the transmission circuit 2 such as a dialer such as TMF is activated from the power-down state, the output signal of the transmission circuit 2 becomes as shown in FIG.
As shown in (b), since the signal changes so as to rise sharply at the starting point A, this signal change is supplied to the non-inverting input terminal of the operational amplifier OP1 via the resistor R4 and the capacitor C5 and is amplified. Is supplied to the transistor Tr1 via the capacitor C2.
The signal waveform to be supplied to the transistor Tr1 is a peaked waveform having a high amplitude as shown by a dotted line in FIG. 2C, but since the Zener diode ZD1 is connected to the base of the transistor Tr1. a high voltage amplitude of該尖head waveforms by the Zener voltage V _ZD1 of the Zener diode ZD1 is cut, and FIG. 2 (c)
The signal suppressed to a relatively small voltage as indicated by the solid line is supplied to the transistor Tr1. Therefore, the signal transmitted from the collector of the transistor Tr1 to the transmission line such as the telephone line via the resistor R1 becomes a signal of a relatively small voltage with the dotted line portion cut off as shown in FIG. 2 prevents power-down noise from being transmitted to the transmission line. The voltage waveform shown in FIG. 2A is the voltage waveform at the connection point between the resistor R1 and the collector of the transistor Tr1.

When a signal is received, the transmitting circuit 2 outputs only a DC component, and the operational amplifier OP1 controls the transistor Tr1 so that the signal having the waveform shown in FIG. The signal input to the terminal T2 from the transmission line is terminated in an alternating manner by the resistor R1.

FIG. 3 is a circuit diagram of a transmission input / output circuit according to another embodiment of the present invention. The transmission input / output circuit shown in the figure is the same as the circuit shown in FIG.
A first filter circuit 5 and a second filter circuit 4 are provided instead of the series circuit of R5 and the series circuit of the resistor R3 and the capacitor C4, and the Zener diode Z connected to the base of the transistor Tr1.
The only difference is that D1 has been removed. The Zener diode ZD1 may be connected as shown in FIG. 1, but is omitted for simplicity.

In the first filter circuit 5, resistors R12 and R13 are connected in series between the transmission circuit 2 and the capacitor C5, and a capacitor C8 is connected between the connection point of the resistors R12 and R13 and the ground. Configuration. Also,
In the receiving circuit 3, capacitors C6 and C7 are connected in series between one end of the resistor R1 and one end of the capacitor C4, and a resistor R10 is connected in parallel to the capacitors C6 and C7 connected in series. In this configuration, a resistor R11 is connected between the connection point of the connected capacitors C6 and C7 and the ground.

The first filter circuit 5 and the second filter circuit 4 thus configured constitute a low-pass filter, thereby removing unnecessary noise components from the fundamental wave of the transmission analog signal to be transmitted to the transmission line. It is assumed that. Although the filter circuits 4 and 5 constitute a low-pass filter as an example, the present invention is not limited to this. For example, a band-pass filter may be used.

FIG. 4 shows a configuration of a general T-bridge low-pass filter using the first filter circuit 5 and the second filter circuit 4. By using the filter circuit configured as described above for the transmission input / output circuit as shown in FIG.
That is, the noise component with respect to the transmission signal output waveform fundamental wave can be reduced.

In each of the above embodiments, the transistor T
Although r1 is used, a variable resistance element such as a photocoupler can be used instead. In addition, although the AC coupling is performed using the capacitor C5, the capacitor C5 may be short-circuited and the resistors R8 and R9 may be removed to perform DC coupling. Furthermore, it is also possible to simply bias the transistor Tr1 and remove the resistor R7.

[0026]

As described above, according to the present invention,
By control means including, for example, a Zener diode connected between the AC coupling means and the variable resistance means, noise of a predetermined voltage value or more supplied to the variable resistance means is reduced,
As a result, the on-resistance of the resistance variable unit is reduced to a predetermined value or less, and is prevented from being transmitted to the transmission line as noise. For example, a transmission circuit such as an FSK modulator or a DTMF dialer is started from a power-down state. It is possible to prevent the noise generated due to the sudden change of the output of the transmission circuit from being output to the transmission line, thereby preventing the device from malfunctioning.

According to the present invention, the first filter means is connected to the non-inverting input terminal of the operational amplifier to which the transmission signal is supplied, and the second filter means is provided in the AC amount feedback means. Therefore, it is possible to prevent unnecessary noise components from being supplied to the operational amplifier.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a transmission input / output circuit according to one embodiment of the present invention.

FIG. 2 is a signal waveform diagram of each part of the transmission input / output circuit shown in FIG.

FIG. 3 is a circuit diagram of a transmission input / output circuit according to another embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a general T-bridge low-pass filter using a filter circuit used in the transmission input / output circuit shown in FIG.

FIG. 5 is a configuration diagram of a conventional transmission input / output circuit.

[Explanation of symbols]

 2 Transmission circuit 3 Receiving circuit 4 Second filter circuit 5 First filter circuit OP1 Operational amplifier Tr1 Transistor (variable resistance element) ZD1 Zener diode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-220562 (JP, A) JP-A-63-103530 (JP, A) JP-A-60-132064 (JP, U) JP-A-60-120 184348 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04M 11/00-11/10 H04B 3/00-3/60

Claims (2)

(57) [Claims] 1. A transmission input / output circuit connected to a transmission terminal device for transmitting and receiving a transmission signal to and from a transmission line, wherein an analog transmission signal to be transmitted to the transmission line is supplied to a non-inverting input terminal. An operational amplifier for amplifying the signal,
AC coupling means connected to the output side of the operational amplifier to output the AC component of the output signal of the operational amplifier to the transmission line, and one end connected to the transmission line to determine the AC input / output impedance for the transmission line. A resistance means is connected between the other end of the resistance means and the AC coupling means so as to have an on-resistance for varying the line impedance of the transmission line, and is connected by the impedance of the transmission line, the resistance means and the on-resistance. A resistance voltage dividing circuit is formed, the on-resistance is changed by a transmission signal at the time of transmission, the transmission signal is transmitted to the transmission line by the change of the on-resistance, the reception AC impedance is determined at the time of reception, and a constant AC is determined at the time of transmission and reception. A variable resistance means for forming an input / output impedance; one end connected between the variable resistance means and the resistance means, and the other end connected to the input of the operational amplifier; And an AC amount feedback unit that feeds back an AC amount to the operational amplifier, and is connected between an output of the operational amplifier and an inverting input terminal, and feeds back a DC amount of an output signal of the operational amplifier to the operational amplifier. DC amount feedback means, which is connected between the AC coupling means and the resistance variable means, a noise of a predetermined voltage value or more is supplied to the variable resistance means, and the ON resistance of the resistance variable means is reduced to a predetermined value or less. A transmission input / output circuit comprising: control means for controlling so as to prevent noise from being reduced and being transmitted to a transmission line; and reception means for alternately extracting a reception signal from the transmission line. 2. A transmission input / output circuit connected to a transmission terminal device for transmitting and receiving a transmission signal to and from a transmission line, wherein an analog transmission signal to be transmitted to the transmission line is supplied to a non-inverting input terminal. An operational amplifier for amplifying the signal,
AC coupling means connected to the output side of the operational amplifier to output the AC component of the output signal of the operational amplifier to the transmission line, and one end connected to the transmission line to determine the AC input / output impedance for the transmission line. A resistance means is connected between the other end of the resistance means and the AC coupling means so as to have an on-resistance for varying the line impedance of the transmission line, and is connected by the impedance of the transmission line, the resistance means and the on-resistance. A resistance voltage dividing circuit is formed, the on-resistance is changed by a transmission signal at the time of transmission, the transmission signal is transmitted to the transmission line by the change of the on-resistance, the reception AC impedance is determined at the time of reception, and a constant AC is determined at the time of transmission and reception. A variable resistance means for forming an input / output impedance; one end connected between the variable resistance means and the resistance means, and the other end connected to the input of the operational amplifier; And an AC amount feedback unit that feeds back an AC amount to the operational amplifier, and is connected between an output of the operational amplifier and an inverting input terminal, and feeds back a DC amount of an output signal of the operational amplifier to the operational amplifier. And a first filter means connected to a non-inverting input terminal of the operational amplifier to which the transmission signal is supplied so as to remove unnecessary noise components supplied to a non-inverting input terminal of the operational amplifier. Provided in the AC amount feedback means,
A transmission input / output circuit comprising: second filter means for preventing unnecessary noise components from being supplied to the operational amplifier; and reception means for alternately extracting a reception signal from a transmission line.