Variable gain amplifier
AssigneeHitachi, Ltd.
InventorsKazuo Kato, Takao Sasayama, Takashi Sase
Life of this patent
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Abstract
A variable gain amplifier includes an amplifier for amplifying an input signal, a switch controlled with a given duty factor and a smoothing filter connected to the switch. The filter and the switch constitutes a negative feedback loop for the amplifier of which amplification factor is variably controlled by varying the duty factor of the switch.
Claims30
In a variable gain amplifier apparatus having means for receiving an input signal, at least one amplifier means including an amplifier for amplifying the received input signal, switch means controlled in on-off operation thereof with a given duty factor in response to an externally applied control signal, and a smoothing filter connected to said switch means, wherein the amplification factor of said amplifier means is varied by varying the duty factor of said switch means, the improvement comprising a negative feedback loop of said amplifier means is composed of said switch means and said smoothing filter in series and said smoothing filter having a time constant which is greater than the on-off period of said switch means.
A variable gain amplifier apparatus comprising an operational amplifier having a plus input terminal to which an input signal is to be applied, a minus input terminal and an output terminal;
- and a negative feedback circuit connected between the output terminal and the minus input terminal of said operational amplifier, including a smoothing filter and switching means connected in series with said smoothing filter and having a control terminal connected to receive an externally applied control signal having a controllable duty cycle for controlling the gain of said operational amplifier according to said duty cycle.
A variable gain amplifier apparatus comprising an operational amplifier having a plus input terminal to which an input signal is to be applied, a minus input terminal and an output terminal;
- and a negative feedback circuit connected between the output terminal and the minus input terminal of said operational amplifier, including a smoothing filter and switching means connected in series with said smoothing filter and responsive to an applied control signal having a selected duty cycle for controlling the gain of said operational amplifier according to said duty cycle, wherein said switching means comprises first and second transistors connected in series between the output terminal of said operational amplifier and ground, and means for rendering said first and second transistors alternately conductive in response to said applied control signal and in accordance with said selected duty cycle, said smoothing filter being connected between the point of connection of said first and second transistors and the minus input terminal of said operational amplifier.
A variable gain amplifier apparatus comprising an amplifier having a minus input terminal to which an input signal is to be applied and an output terminal;
- a smoothing filter connected to the minus input terminal of said amplifier;
- and switching means connected to said smoothing filter and responsive to an applied control signal having a selected duty cycle for alternately connecting said input signal and the output terminal of said amplifier to said smoothing filter to control the gain of said amplifier according to said duty cycle.
Dependencies are inferred from the claim text.