# US 5,703,518 A · Absolute value circuit capable of providing full-wave rectification with less distortion

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- Number: US 5,703,518 A
- Document ID: US5703518A
- Status: Granted
- Kind: A
- Application number: 08/757,949
- Filed: 1996-11-22
- Granted: 1997-12-30
- Earliest claimed: 1994-08-01
- Assignees: Oki Electric Industry Co., Ltd.
- Inventors: Syouhei Yamamoto
- Web page: https://patentgrep.com/patent/US5703518A

## CPC

- G01R 19/22: using conversion of AC into DC
- G06G 7/25: for discontinuous functions, e.g. backlash, dead zone, limiting absolute value or peak value {(measuring the maximum value of currents or voltages G01R19/30)}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G06G: ANALOGUE COMPUTERS (analogue optical computing devices G06E3/00)

## Abstract

An absolute value circuit according to the present invention has a configuration wherein a switch is connected directly to an output of an amplifier and an output terminal. Owing to this configuration, the absolute value circuit can be realized which is capable of providing full-wave rectification with less distortion.

## Claims

### Claim 1

An absolute value circuit, comprising:
an input terminal to receive an input voltage;
an output terminal;
an input resistor;
a feedback resistor, the input resistor and the feedback resistor being coupled in series between the input and output terminals, the input resistor being coupled to the feedback resistor at an intermediate coupling node;
an operational amplifier having a first input, a second input, and an amplifier output, the first input of the operational amplifier being coupled to the intermediate coupling node, the second input of the operational amplifier receiving a reference voltage;
comparing means for determining whether or not the input voltage exceeds the reference voltage; and
a switch to electrically couple the amplifier output to the output terminal and the feedback resistor when the reference voltage exceeds the input voltage and to electrically isolate the amplifier output from the output terminal and the feedback resistor when the input voltage exceeds the reference voltage, the switch being coupled to the comparing means.

### Claim 2 (depends on 1)

The absolute value circuit of claim 1, wherein the switch comprises a MOSFET having a source and a drain, one of which is coupled to the amplifier output and the other of which is coupled to the output terminal.

### Claim 3 (depends on 1)

The absolute value circuit of claim 1, wherein the first input of the operational amplifier is an inverting input and the second input is a non-inverting input.

### Claim 4 (depends on 3)

The absolute value circuit of claim 3, wherein the comparing means comprises another operational amplifier which serves as a comparator, the another operational amplifier having an inverting input that receives the reference voltage and a non-inverting input that is coupled to the input terminal.

### Claim 5

An absolute value circuit, comprising:
an input terminal to receive an input voltage;
an output terminal;
comparing means for determining whether or not the input voltage exceeds a reference voltage;
a first switch to electrically couple the input terminal to the output terminal when the input voltage exceeds the reference voltage, the first switch including a first MOSFET having a source and a drain, one of which is coupled to the input terminal and the other of which is coupled to the output terminal, the first MOSFET additionally having a gate which is coupled to the comparing means;
an operational amplifier having a first input, a second input, and an amplifier output, the second input receiving the reference voltage;
an input resistor;
a feedback resistor, the input resistor and the feedback resistor being coupled in series between the input terminal and the amplifier output, the input resistor being coupled to the feedback resistor at an intermediate coupling node, the intermediate coupling node being coupled to the first input of the operational amplifier; and
a second switch to electrically couple the amplifier output to the output terminal when the reference voltage exceeds the input voltage, the second switch including a second MOSFET having a source and a drain, one of which is connected to the amplifier output and the other of which is connected to the output terminal, the second MOSFET additionally having a gate which is coupled to the comparing means.

### Claim 6 (depends on 5)

The absolute value circuit of claim 5, wherein the first input of the operational amplifier is an inverting input and the second input is a non-inverting input.

### Claim 7 (depends on 6)

The absolute value circuit of claim 6, wherein the comparing means comprises another operational amplifier which serves as a comparator, the another operational amplifier having an inverting input that receives the reference voltage and a non-inverting input that is coupled to the input terminal.