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US 4,234,853 AGranted
Automatic level control circuit
AssigneeTokyo Shibaura Denki Kabushiki Kaisha
InventorHiroyasu Yamaguchi
Life of this patent
Estimating the term…
Abstract
An automatic level control circuit including a current controlled attenuator wherein the amount of attenuation is controlled by a control current, an amplifier for amplifying an output signal of the attenuator, a current rectifier for forming a DC current source in accordance with the amplitude of the output signal voltage from the amplifier, and a current shunt for absorbing an output current fed from the rectifier. The control current is produced as a difference between the current from the rectifier and the current absorbed by the shunt. When the current fed from the rectifier is larger than that absorbed by the shunt, the automatic level control circuit operates in a manner that, when its input signal is at low level, the circuit gain is large and, as the input signal level rises, the circuit gain drops.
Claims25
An automatic level control circuit for controlling the level of an input signal comprising:
- a gain controlled circuit having input, output and control ports, said input port for coupling to said input signal to be level controlled and said output port supplying a level controlled output signal, the gain of said gain controlled circuit being controllable responsive to a control current applied to said control port, said gain controlled circuit including at least one variable impedance element, the impedance of which is a function of said control current;
- and
- a control current source for supplying said control current, said control current being a function of the difference between a direct current component corresponding to the level of said input signal and a reference current;
- wherein the output impedance of said control current source is high so that said control current is substantially independent from the temperature change of the voltage drop occurring across said variable impedance element.
1 more element
An automatic level control circuit for controlling the level of an input signal comprising:
- a gain controlled circuit having input, output and control ports, said input port for coupling to said input signal to be level controlled and said output port supplying a level controlled output signal, the gain of said gain controlled circuit being controllable responsive to a control current applied to said control port, said gain controlled circuit including at least one variable impedance transistor, the base-emitter impedance of which is a function of said control current;
- and
- a control current source for supplying said control current, said control current being a function of the difference between a direct current component corresponding to the level of said input signal and a reference current;
- wherein the output impedance of said control current source is high so that said control current is substantially independent of the temperature change of or the voltage drop across the base-emitter junction of said variable impedance transistor.
1 more element
An automatic level control circuit for controlling the level of an input signal comprising:
- a gain controlled circuit having input, output and control ports, said input port for coupling to said input signal to be level controlled and said output port supplying a level controlled output signal, the gain of said gain controlled circuit being controllable responsive to a control current applied to said control port, said gain controlled circuit including at least one variable impedance element, the impedance of which is a function of said control current;
- and
- a control current source for supplying said control current, said control current being a function of the difference between a direct current component corresponding to the level of said input signal and a reference current, said control current source comprising:
- a current rectifier for providing a first current including said direct current component corresponding to the level of said input signal of said gain controlled circuit, the output of said current rectifier for coupling to said control port of said gain controlled circuit, said current rectifier comprising:
- a first current source transistor having a collector wherein said first current flows:
- a compensating amplifier having an inverting input terminal and an output terminal coupled to the emitter and base of said first current source transistor, respectively, in order to neutralize the temperature function of said first current;
- and
- a first resistor for setting the ratio of the magnitude of said control current to said output signal level of said gain controlled circuit, said first resistor being coupled at one end to the inverting input terminal of said compensating amplifier and being coupled at its other end to the input terminal of said gain controlled circuit;
- and
- a current shunt, also coupled to the output of said current rectifier, for absorbing a second current corresponding to a reference current having a predetermined magnitude, whereby said control current is made to be the difference between said first and second currents.
7 more elements
An automatic level control circuit for controlling the level of an input signal comprising:
- a gain controlled circuit having input, output and control ports, said input port for coupling to said input signal to be level controlled and said output port supplying a level controlled output signal, the gain of said gain controlled circuit being controllable responsive to a control current applied to said control port, said gain controlled circuit including at least one variable impedance element, the impedance of which is a function of said control current;
- and
- a control current source for supplying said control current, said control current being a function of the difference between a direct current component corresponding to the level of said input signal and a reference current, said control current source comprising:
- a current rectifier for absorbing a first current including said direct current component corresponding to the level of said input signal, said current rectifier comprising:
- a first current source transistor having a collector wherein said first current flows:
- a compensating amplifier having an inverting input terminal and an output terminal coupled to the emitter and base of said first current source transistor, respectively, in order to neutralize the temperature function of said first current;
- and
- a first resistor for setting the ratio of the magnitude of said control current to said output signal level of said gain controlled circuit, said first resistor being coupled at one end to the inverting input terminal of said compensating amplifier and being coupled at its other end to the output terminal of said gain controlled circuit;
- and
- a shunt coupled to the output of said current rectifier for conducting a second current corresponding to said reference current having a predetermined magnitude, said shunt being coupled to a circuit thorugh which said first current flows in order to produce said control current equal to the difference between said first and second currents.
7 more elements
An automatic level control circuit comprising:
- a gain controlled circuit for automatically level-controlling an input signal to produce an output signal that is automatically level-controlled, said gain controlled circuit including a variable impedance element having an impedance controllable by a control current;
- and
- a control current source for supplying said control current equal to the difference between a direct current component corresponding to the input signal level of said gain controlled circuit and a reference current, said control current source comprising:
- a current rectifier for providing a first current including a direct current component corresponding to the level of said input signal of said gain controlled circuit, said current rectifier comprising:
- a first current source transistor having a collector in which said first current flows;
- a compensating amplifier having an inverting input terminal and the output terminal coupled to the emitter and base of said first current source transistor, respectively, in order to neutralize the temperature change of said first current;
- and
- a first resistor for setting the ratio of the magnitude of said control current to the output signal level of said gain controlled circuit, said first resistor being coupled at one end to the inverting input terminal of said compensating amplifier and being coupled at its other end with the output signal from said gain controlled circuit;
- and
- a current shunt for absorbing a second current corresponding to said reference current magnitude, said current shunt being coupled to a circuit through which said first current flows in order to produce said control current equal to the difference between said first and second currents;
- and
- means for compensating the temperature coefficient of said control current so that the temperature coefficient of said control current source is substantially zero.
9 more elements
An automatic level control circuit comprising:
- a gain controlled circuit for automatically level-controlling an input signal to produce an output signal that is automatically level-controlled, said gain controlled circuit including a variable impedance element having an impedance controllable by a control current;
- control current source for supplying said control current equal to the difference between a direct current component corresponding to the input signal level of said gain controlled circuit and a reference current, said control current source comprising:
- current rectifier means for absorbing a first current including a direct current component corresponding to the level of said input signal of said gain controlled circuit, said current rectifier comprising:
- a current source transistor having a collector in which said first current flows;
- a compensating amplifier having an inverting input terminal and the output terminal coupled to the emitter and base of said first current source transistor, respectively, in order to neutralize the temperature change of said first current;
- and
- a first resistor for setting the ratio of the magnitude of said control current to the output signal level of said gain controlled circuit, said first resistor being coupled at one end to the inverting input terminal of said compensating amplifier and being coupled at its other end with the output signal from said gain controlled circuit;
- and
- a shunt for feeding a second current corresponding to said reference current having a predetermined magnitude, said shunt being coupled to a circuit through which said first current flows in order to supply said controll current equal to the difference between said first and second currents;
- and
- means for compensating the temperature coefficient of said control current so that the temperature coefficient of said control current source is substantially zero.
8 more elements
An automatic level control circuit according to either of claims 60 or 61, wherein said control current source includes control current changing means for changing said control current in accordance with the voltage dropping of a power source, in order to reduce the upper limit level of said output signal which is automatically controlled by the automatic level control circuit in accordance with the reduction of the power source voltage to be applied to circuit coupled to said automatic level control circuit.
Dependencies are inferred from the claim text.