JPH04245839A - Transmission output circuit - Google Patents

Abstract

PURPOSE:To realize automatic adjustment so as to make the adjustment of the variance of a transmission circuit, etc., unnecessary, and further, to lower cost. CONSTITUTION:The AC amplitude of a transmission signal from the transmission circuit 1 amplified by an amplifier 2 and the amplitude of reference voltage Vref are compared with each other by OP2, and the amplification degree of the amplifier 2 is adjusted by varying a variable resistance element 4 through an integrator 3 by a signal the comparing means outputs when the AC amplitude of the transmission signal is larger.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission output circuit that requires no adjustment and is low cost.

0002

2. Description of the Related Art FIG. 3 shows a conventional example. T1 and T2 are connected to a telephone line through terminals. The transmitted signal appears at T2. Reference numeral 1 denotes a transmission circuit that generates a transmission signal, such as a DTMF dialer or FSK MODEM, and is connected to the amplifier 2 via a variable resistor VR1. The amplifier 2 amplifies the DTMF signal and FSK signal output from the transmitting circuit 1 to a desired level, and in this example, the operational amplifier OP1 and the resistor R
2, an inverting amplifier consisting of R3. amplifier 2
The degree of amplification is varied by a variable resistor VR1. C1 is a capacitor provided for the purpose of AC coupling the transmission signal amplified by the amplifier 2 to the telephone line. R1 is a resistor provided for the purpose of determining the output impedance to the telephone line, and is usually selected to be about 600Ω.

0003

[Problems to be Solved by the Invention] In such a conventional circuit, since there are variations in the transmitting circuit 1 and variations in the capacitor C1, it is necessary to adjust the amplifier so that the output level from the terminal T2 becomes a desired level using the variable resistor VR1. It was necessary to adjust the amplification degree of 2. Furthermore, since the variable resistor VR1 is expensive, the product itself is expensive. An object of the present invention is to provide a low-cost transmission output circuit that does not require adjustment. [Structure of the invention]

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an amplifying means for connecting an output end to one input end via a feedback resistor, and an AC amplitude of a transmission signal amplified by the amplifying means. and an amplitude of the reference voltage, an integrator that integrates the signal output by the comparison means when the AC amplitude of the transmission signal is larger than the amplitude of the reference voltage, and an integrator connected in parallel to the feedback resistor of the amplification means. It consists of variable resistance means that is varied by the output signal of the integrator.

[0005]

[Operation] In such a configuration, the comparing means compares the AC amplitude of the transmission signal with the amplitude of the reference voltage, outputs a signal when the AC amplitude of the transmission signal is larger, and outputs this signal via the integrator. Since the variable resistance means is varied by the signal to adjust the amplification degree of the amplification means, the effort of adjustment can be saved and costs can be reduced.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a transmission output circuit according to the present invention. T
1 and T2 are terminals connected to the telephone line. The transmission signal is T
Appears in 2. 1 is DTMF dialer or FSK MO
Amplifier 2 is a transmitting circuit that generates a transmission signal such as a DEM.
It is connected to the. The amplifier 2 amplifies the DTMF signal and FSK signal output from the transmitting circuit 1 to a desired level. In this example, it consists of an operational amplifier OP1 and resistors R2 and R3, and a variable resistance element 4 is connected in parallel to the resistor R2. C1 is a capacitor provided for the purpose of AC coupling with the telephone line. R1 is a resistor provided for the purpose of determining the output impedance to the telephone line, and is usually selected to be about 600Ω. The capacitor C2 is provided for the purpose of applying an alternating current to the comparator OP2, and the comparator OP2 side is biased to the ground potential by a resistor R4.

Next, the operation will be explained. Comparator OP2 has the reference voltage Vref connected to the - terminal side, and when the input voltage on the + terminal side becomes lower than the voltage on the - terminal side, 'L
'Output the level. Vref is a reference voltage, the + side is grounded, and the - side is connected to the - terminal of the comparator OP2. If the reference voltage Vref is outputting vr, -vr will be applied to the - terminal of the comparator OP2. The reference voltage Vref is often constructed using a Tuner diode, a bandgap reference, or a power supply voltage. D1 is a diode through which current flows and conducts with the integrator 3 only when the output of the comparator OP2 is at the 'L' level. 3 is an integrator, which is composed of an operational amplifier OP3, a resistor R5, and a capacitor C3.The output of the integrator 3, which integrates the 'L' level voltage of the comparator OP2, is connected to a variable resistance element 4, which controls the amplification degree of the amplifier 1. There is. 4
is a resistance variable element, which is represented by a Cds photocoupler in this example. The LED side is connected to the integrator 3 via a resistor R6, and the resistor side is connected in parallel with the resistor R2 of the amplifier 1. As the current on the LED side increases, the resistance on the resistor side decreases.

FIG. 2 shows a waveform diagram. From transmitter circuit 1 (
a) A waveform like this is output. Signal a is amplified by amplifier 2 and passes through capacitor C1 to T2 for AC coupling to the telephone line. Here, it is assumed that the AC component of the signal passing through the capacitor C1 becomes (b) and the desired output amplitude is 2Va ((1) of waveform b). Signal b is applied to comparator OP2 by capacitor C2. Capacitor C2 is provided for the purpose of transmitting only the alternating current component to comparator OP2. - of comparator OP2
A reference voltage Vref is connected to the terminal side, and the voltage vr of this reference voltage Vref is selected so that vr=Va. In other words, since the + side of the reference voltage is grounded, -vr is applied to the - terminal side of the comparator OP2. Therefore, when the voltage of signal b input to the + terminal side of comparator OP2 falls below the - terminal side voltage -vr9l ((2) of waveform b), that is, when signal b exceeds the desired input voltage amplitude 2Vb, comparator OP2
The output becomes 'L' ((3) of waveform b). here,
A current flows through the diode D1 and conducts with the integrator 3.The integrator 3 then integrates the 'L' level voltage of the comparator OP2 and outputs a voltage like d. In other words, when the output of comparator OP2 becomes 'L' level, it becomes 'L'.
During the level, the integrator 3 performs an integration operation ((of waveform d)
5) ), when the current changes from 'L' level to 'H' level, the current at that time continues ((6) of waveform d). When the output of the comparator OP2 becomes 'L' level again, the integrator 3 performs an integrating operation ((7) of waveform d). This operation is repeated until vr = va. The signal d is converted into a current by the resistor R6 and flows into the variable resistance element 4, and when the current on the LED side increases, the resistor R of the amplifier 2
The resistance of the resistor connected in parallel with 2 decreases. When the resistance on the resistor side of the variable resistance element 4 decreases, the amplification degree of the amplifier 2 decreases, and the amplitude of the signal b decreases accordingly. A desired amplitude can be obtained by repeating the above operation and controlling the amplification degree by the circuit.

[0009]

As described above, in the present invention, the variable resistance means for adjusting the amplification degree of the amplification means is varied by the signal output by the comparison means when the AC amplitude of the transmission signal becomes larger than the amplitude of the reference voltage. Therefore, it is possible to obtain a low-cost transmission output circuit that can be automatically adjusted.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a transmission output circuit of the present invention.

FIG. 2 is a waveform diagram showing the operation of the transmission output circuit of the present invention.

FIG. 3 is a configuration diagram of a conventional transmission output circuit.

[Explanation of symbols]

Claims (1)

[Claims] 1. Amplifying means for connecting an output end to one input end via a feedback resistor; comparing means for comparing the AC amplitude of the transmission signal amplified by the amplifying means with the amplitude of the reference voltage; an integrator that integrates the signal output by the comparison means when the AC amplitude is larger than the amplitude of the reference voltage; and variable resistance means that is connected in parallel to the feedback resistor of the amplification means and is varied by the output signal of the integrator. A transmission output circuit having.