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Amplifier-circuit-free-from-leakage-between-input-and-output-ports

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Amplifier circuit free from leakage between input and output ports

Details

Inventors: Masuda, Shinji;
Assignee: NEC Corporation (Tokyo, JP)
Primary Examiner: Miller; Stanley D.
Assistant Examiner: Callahan; Timothy P.
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis

A leakage current between the inverting input terminal and the output terminal of an operational amplifier having a switch between the two terminals is prevented from flowing by equalizing the potentials at the two terminals of the switch when it is open. This is accomplished by dividing the switch into two and inserting an additional switch between the intermediate node of the divided two switches and a reference potential point.

DETAILED DESCRIPTION The object of the present invention is to provide a circuit producing an output signal free from the leakage of charges between an output and input ports.
Another object of the present invention is to provide a coefficient multiplying circuit which does not generate leakage currents through the switches between an output and input ports when the switches are turned off.
The circuit according to the present invention comprises an operational amplifier and a first analog switch coupled between the inverting input terminal of the operational amplifier and the output terminal of the operational amplifier, the non-inverting input terminal of the operational amplifier is connected to the ground or a reference potential terminal and is characterized by further comprising a second analog switch inserted between the first analog switch and the output terminal of the operational amplifier and a third analog switch coupled between the non-inverting input terminal of the operational amplifier and the connection point of the first and second analog switches.
According to the circuit of the present invention, one terminal of the first analog switch is connected to the inverting input port of the operational amplifier.
The inverting input port is nearly at the ground or reference potential, when the operational amplifier is balanced, because the non-inverting input port is connected to the ground or the reference potential terminal.
The other terminal of the first analog switch is connected, when it is OFF state, to the ground or the reference potential terminal through the third analog switch.
The third analog switch is turned on when the first analog switch is turned off, while the second analog switch operates together with the first analog switch.
Since the both terminals of the first analog switch are maintained at the same ground or reference potential when the first analog switch is turned off, substantially no potential difference exists across the both terminals and any leakage current does not flow through the first analog switch

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