Switched capacitor amplifier circuit

• US 5,475,337 A
• Filed: 02/21/1995
• Issued: 12/12/1995
• Est. Priority Date: 07/24/1992
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Tatsumi, Satoshi
• Primary Examiner(s): Gross, Anita Pellman
• Assistant Examiner(s): NGUYEN, TIEP HUU
• Application Number:
  US08/391,274
• Time in Patent Office: 294 Days
• Field of Search: 307/491, 307/520, 307/542, 307/246, 328/162, 328/165, 327/554, 327/551, 327/552, 327/563, 327/334, 327/565, 330/252, 330/260, 330/51, 330/9
• US Class Current: 327/551
• CPC Class Codes: H03F 3/005 using switched capacitors, e.g. dynamic amplifiers; using switched capacitors as resistors in differential amplifiers H03F3/45 takes precedence

Abstract

In a switched capacitor amplifier circuit of an offset cancellation type, a capacitor is arranged between a reverse input terminal of an operational-transconductance amplifier and a reference voltage. Only in an offset cancelling operation in which a first group of switches are on, the capacitor functions as a load of the amplifier. The capacitor hence does not exert any influence upon transfer of charge. With provision of the circuit, the phenomenon of oscillation is suppressed in the operation to cancel the offset voltage.

Claims

1. A switched capacitor amplifier circuit in which an offset voltage is cancelable, comprising:

an operational amplifier provided with a reverse input terminal connected to an input voltage and a non-reverse input terminal connected to a reference voltage, said operational amplifier amplifying a voltage difference between the input voltage and the reference voltage to produce an output voltage at an output terminal of said circuit, to thereby produce the offset voltage due to the voltage difference at the output terminal, and

a capacitor added to said operational amplifier, said capacitor being connected between the reverse input terminal and the reference voltage, so that said capacitor serves as a load for said operational amplifier only when the offset voltage is canceled in said circuit.

2. A switched capacitor amplifier circuit in which an offset voltage is cancelable, comprising:

an operational amplifier provided with a reverse input terminal connected to an input voltage and a non-reverse input terminal connected to a reference voltage, said operational amplifier amplifying a voltage difference between the input voltage and the reference voltage to produce an output voltage at an output terminal of said circuit, to thereby produce the offset voltage due to the voltage difference at the output terminal, and

a capacitor added to said operational amplifier, said capacitor being connected between the reverse input terminal and the reference voltage, so that said capacitor serves as a load for said operational amplifier only when the offset voltage is canceled in said circuit;

another capacitor connected between the reverse input terminal and a signal input terminal of said circuit;

a first switch interconnected between said another capacitor and the signal input terminal;

a second switch connected between an interconnection between said another capacitor and said first switch, and the reference voltage;

still another capacitor connected between the reverse input terminal and the output terminal;

a third switch connected between the reverse input terminal and the output terminal;

a fourth switch interconnected between said still another capacitor and the reverse input terminal;

a fifth switch connected between an interconnection between said fourth switch and said still another capacitor, and the reference voltage;

a first switch group consisting of said first, said third, and said fifth switches;

a second switch group consisting of said second and said fourth switches; and

said first and said second switch groups turning on and off in accordance with a first clock signal and a second clock signal that are separated from each other and shifted relative to each other by half a period thereof.

3. The circuit as claimed in claim 2, wherein:

said operational amplifier comprises an operational-transconductance amplifier.

4. A switched capacitor amplifier circuit, comprising:

an operational-transconductance amplifier having a non-reverse input terminal connected to a reference voltage;

a first capacitor connected between a reverse input terminal of the amplifier and the reference voltage;

the first capacitor serving as a load of the amplifier only when the circuit achieves cancellation of an offset voltage;

a second capacitor connected to the reverse input terminal of the amplifier;

a first switch connected between the second capacitor and a signal input terminal of the circuit;

a second switch connected between the second capacitor and the reference voltage;

a third switch connected between the reverse input terminal of the amplifier and an output terminal of the circuit;

a fourth switch and a third capacitor connected between the reverse input terminal of the amplifier and the output terminal of the circuit in parallel with the third switch; and

a fifth switch connected between the fourth switch, the third capacitor, and the reference voltage;

a first switch group consisting of the first, third, and fifth switches; and

a second switch group consisting of the second and fourth switches;

said first and said second switch groups turning on and off in accordance with a first clock signal and a second clock signal that are separated from each other and shifted relative to each other by half a period thereof.