JPH0125244B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic level control amplifier with an on/off switch used in a circuit of a wireless communication device that communicates by modulating a high frequency carrier wave.

BACKGROUND ART In wireless communication in which one high-frequency carrier wave is modulated by one audio channel for communication, the presence or absence of audio is detected and the carrier wave is cut off when there is no audio. SCPC especially in satellite communications
In this method, intermittent carrier waves are required depending on the presence or absence of voice in order to reduce cross-modulation of satellite repeaters.

In addition, in FM-SCPC satellite communication,
Only a small output level deviation from the designated value of the carrier wave is allowed, and must be suppressed to within ±0.5 dB, for example.

For this reason, a circuit as shown in FIG. 1 has conventionally been used. In FIG. 1, a variable attenuator 1,
The amplifier 2, the detector 3, and the controller 4 constitute an amplifier circuit with automatic level control.The high-frequency signal input to the input terminal 5 is kept at a constant level by this amplifier circuit, and then is switched on and off by the switch circuit 6. , and is outputted from an output terminal 8 via a buffer amplifier 7 provided to avoid fluctuations in output impedance due to switching on and off. However, in such a circuit configuration, the output level fluctuates due to gain fluctuations due to ambient temperature fluctuations of the switch circuit and buffer amplifier, and gain fluctuations due to the amplitude frequency characteristics.To reduce this, temperature compensation and changes in the amplitude frequency characteristics are necessary. There was a problem that equalization etc. were required and the circuit became extremely complicated.

In order to eliminate such problems, a circuit as shown in FIG. 2 has been devised.

In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. In this circuit configuration, since the amplifier circuit with automatic level control is provided after the switch circuit 6, steady output level fluctuations can be compressed by this circuit, but the input level of the amplifier circuit with automatic level control There is a problem with the generation of harmful transient responses in the output level to discontinuities. That is, when the input signal turns on as shown in FIG. 3a, the output signal causes an excessive overshoot at the moment the input signal turns on, as shown in FIG. 3b. The reason for this is that in automatic level control, the amplifier circuit is at its maximum gain when the input signal is off, and only after a certain response time has elapsed since the input signal is turned on does it reach its normal gain.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide an automatic level control amplifier with an on/off switch which has a simple circuit construction and which does not produce harmful transient responses.

In order to achieve such an object, the present invention provides a differential amplifier that controls the level of the high-frequency amplifier circuit by amplifying the difference voltage between the output voltage obtained by detecting the high-frequency output of the amplifier circuit and the reference voltage. A resistor, a capacitor, and a switch circuit for inputting a reference voltage are connected in parallel to the reference voltage input terminal of the dynamic amplifier, and a resistor for inputting a predetermined voltage is connected to the detection output voltage input terminal. Further, a second switch circuit is connected in series to the power supply circuit of the high frequency amplifier.

Hereinafter, the present invention will be explained in detail based on examples.

FIG. 4 is a circuit diagram of an embodiment of an automatic level control amplifier with an on/off switch according to the present invention. The high frequency signal of the carrier wave inputted to the input terminal 10 is level-controlled by a variable attenuator 11 using a PIN diode, and then amplified by an amplifier 12 for high frequency amplification and outputted to an output terminal 13. Amplifier 12
A part of the output signal is branched and detected by a wave detector 14 to become a DC voltage. This detected output voltage, which has become a DC voltage, is passed through a resistor 15 to a differential amplifier 16.
is applied to the inverting input terminal of In addition to the detected output voltage, a positive voltage for canceling a predetermined voltage is applied from the reference power source 17 via a resistor 18 to this inverting input terminal. Further, a capacitor 19 and a resistor 2 are connected between the inverting input terminal and the output terminal of the differential amplifier 16.
0 parallel circuits are connected.

On the other hand, a reference voltage is applied to the non-inverting input terminal of the differential amplifier 16 from a reference power supply 17 via a resistor 21. A field effect transistor 22 and a capacitor 23 are connected in parallel between this non-inverting input terminal and the ground, and an intermittent control signal input from an input terminal 24 is connected to the gate of the field effect transistor 22 via a resistor 25. It is now available to be added. Note that 26 is a resistor connected between the gate and ground.

In such a configuration, the variable attenuator 1 is controlled by the level control signal output from the differential amplifier 16.
1 is controlled, negative feedback is applied so that the output voltage of the detector 14 becomes equal to the reference voltage from the reference power supply 17 during steady state, and an automatic control operation is performed. Thereby, the output level of the high frequency signal output from the output terminal 13 is maintained at a constant value.

Further, when an intermittent control signal for intermittent high-frequency signals is input to the input terminal 24, the field effect transistor 22 is controlled on/off by this signal, and when it is off, the automatic control operation is not affected at all. is not received, but when it is on, the differential amplifier 16
The non-inverting input terminal of will have a value close to ground potential.
In this way, when the voltage at the non-inverting input terminal becomes almost zero, the output of the differential amplifier 16 is controlled in the negative direction,
As a result, the amount of attenuation of the variable attenuator 11 increases, and the output level of the high frequency signal decreases. In this case, even if the field effect transistor 22 is turned on, it is not completely short-circuited and there is residual resistance, so the potential at the non-inverting input terminal of the differential amplifier 16 shows a positive residual voltage, albeit slightly. Therefore, as it is, the output level of the high frequency signal will not be completely turned off, but will be controlled to a level such that the output voltage of the detector 14 is approximately equal to the residual voltage.

In the circuit configuration of this embodiment, in order to prevent this problem, a positive voltage of a predetermined value is applied from the reference power supply 17 to the inverting input terminal of the differential amplifier 16 for cancellation. This cancellation voltage is set to a value greater than the residual voltage. As a result, when the field effect transistor 22 is on, the voltage at the inverting input terminal of the differential amplifier 16 becomes more positive than the voltage at the non-inverting input terminal even if there is no output voltage from the detector 14, and the voltage at the inverting input terminal of the differential amplifier 16 becomes more positive than the voltage at the non-inverting input terminal. The output of variable attenuator 16 is always controlled fully in the negative direction, and the amount of attenuation of variable attenuator 11 is maximized. Therefore, when the field effect transistor 22 is on, the output level of the high frequency signal is controlled to a sufficiently low level.

Note that when the field effect transistor 22 changes from on to off, the voltage at the non-inverting input terminal rises slowly because the capacitor 23 is connected, and as a result, the output level of the high-frequency signal also rises slowly. Harmful overshoots no longer occur.

FIG. 5 shows signal waveforms of the circuit in FIG. 4, where a is a high frequency signal input from the input terminal 10, b is an intermittent control signal input from the input terminal 24, and c is an output from the output terminal 13. The waveforms of the high-frequency output signals are shown.

As is clear from FIG. 5c, no overshoot occurs in the high frequency output signal even when the control signal is on.

FIG. 6 is a circuit diagram of another embodiment, in which the same or corresponding parts as in FIG. 4 are given the same reference numerals. In the figure, 28 is a switching transistor connected in series to the power supply circuit of the amplifier 12 and turned on and off by an intermittent control signal. Inductors 30 are connected between them. Note that 31 is a capacitor that constitutes a filter together with the inductor 30.

According to this circuit configuration, when the field effect transistor 22 is turned off by the intermittent control signal input to the input terminal 24, the transistor 28 is turned off at the same time.
is also turned off, so even if the amount of attenuation by the variable attenuator 11 is insufficient when the high-frequency output signal is turned off, the power to the amplifier 12 can be turned off to stop its operation. It is possible to obtain excellent isolation.

In the embodiments described above, the positive voltage for cancellation applied to the inverting input terminal of the differential amplifier is supplied from the reference power supply, but it can be supplied from any other suitable power supply.

As explained above, according to the automatic level control amplifier with an intermittent switch according to the present invention, the reference voltage input terminal of the differential amplifier constituting the automatic level control circuit for high frequency signals is turned on and off by the capacitor and the intermittent control signal. By connecting switch circuits in parallel and applying a cancellation voltage to the detection voltage input terminal via a resistor, harmful effects that occur when the output level of high-frequency signals is interrupted by turning on and off the switch circuits can be eliminated. It is possible to prevent overshoot, and since differential amplification is used, the output level is automatically controlled to a constant level regardless of fluctuations in ambient temperature, etc. Furthermore, the automatic level control circuit and switch circuit are integrated into one Since the circuit configuration is integrated into a single unit, the circuit configuration is simplified, and adjustment is made easier, among other advantages. Furthermore, sufficient isolation can be obtained by turning off the power to the amplifier when the high frequency signal is off.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of a conventional example, FIG. 3 is a signal waveform diagram in the circuit of FIG. 2, and FIG. 4 is a circuit diagram of an embodiment of an automatic level control amplifier with an on/off switch according to the present invention. , FIG. 5 is a signal waveform diagram in the circuit of FIG. 4, and FIG. 6 is a circuit diagram of another embodiment. 11...variable attenuator, 12...amplifier, 14...
...Detector, 16...Differential amplifier, 17...Reference power supply, 22...Field effect transistor, 28...Transistor.

Claims (1)

[Scope of Claims] 1. An amplifier circuit comprising a variable attenuator whose attenuation changes depending on a level control signal and an amplifier that amplifies a high-frequency signal; a detector that detects a signal output from the amplifier circuit; A differential amplifier compares the output voltage of the detector with a reference voltage, amplifies the difference voltage, and outputs the level control signal, and the reference voltage input terminal of the differential amplifier is connected to the reference voltage via a resistor. In addition to applying a voltage, a capacitor and a switch circuit that is turned on and off by an intermittent control signal are connected in parallel, and a predetermined voltage is applied to the detection output voltage input terminal of the differential amplifier via a resistor. Automatic level control amplifier with intermittent switch. 2. An amplifier circuit consisting of a variable attenuator whose attenuation changes depending on a level control signal and an amplifier that amplifies a high-frequency signal, a detector that detects the signal output from this amplifier circuit, and an output voltage of this detector. and a differential amplifier that compares and a reference voltage, amplifies the difference voltage, and outputs the level control signal, and a reference voltage is applied to the reference voltage input terminal of the differential amplifier via a resistor, and a capacitor is connected to the reference voltage input terminal of the differential amplifier. and a first switch circuit that is turned on and off by an intermittent control signal are connected in parallel, and a predetermined voltage is applied to the detection output voltage input terminal of the differential amplifier via a resistor, and to the power supply circuit of the amplifier. An automatic level control amplifier with an intermittent switch, characterized in that a second switch circuit connected in series is turned on and off simultaneously with the first switch circuit by the intermittent control signal.