# US 7,411,460 B2 · Elimination of dummy detector on optical detectors using input common mode feedback

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- Number: US 7,411,460 B2
- Document ID: US7411460B2
- Status: Granted
- Kind: B2
- Application number: 11/372,793
- Filed: 2006-03-10
- Published: 2007-09-13
- Granted: 2008-08-12
- Earliest claimed: 2006-03-10
- Assignees: Exar Corporation
- Inventors: Richard W. Randlett
- Web page: https://patentgrep.com/patent/US7411460B2

## CPC

- H03F 3/087: {with IC amplifier blocks (H03F3/085 takes precedence)}
- H03F 1/08: Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements (wide-band amplifiers with inter-stage coupling networks incorporating these impedances H03F1/42)
- H03F 3/45475: {using IC blocks as the active amplifying circuit}
- H03F 3/45928: {using IC blocks as the active amplifying circuit}
- H03F 3/45941: {Controlling the input circuit of the differential amplifier}
- H03F 2203/45061: the common mode reference signal being taken or deducted from the one or more inputs of the differential amplifier
- H03F 2203/45078: the common mode signal being taken or deducted from the one or more inputs of the differential amplifier
- H03F 2203/45424: the CMCL comprising a comparator circuit
- H03F 2203/45561: the IC being controlled, e.g. by a signal derived from a non specified place in the dif amp circuit
- H03F: AMPLIFIERS

## Abstract

A voltage reference forces a constant voltage at the inputs to an amplifier, thereby negating a need for a dummy detector on the non-active input of the amplifier.

## Claims

### Claim 1

A circuit to amplify an electrical signal comprising:
a photo-detector to provide an input signal;
a first amplifier to receive an input signal from the photo-detector and to amplify the input signal to form an output signal, the first amplifier comprising an active input to receive the input signal and a non-active input; and
a second amplifier to force a constant voltage at the active and non-active input of the first amplifier, thereby negating a need for a dummy detector on the non-active input of the first amplifier;
wherein the second amplifier maintains an input common mode voltage at an approximately constant level.

### Claim 2 (depends on 1)

The circuit of claim 1, wherein the photo-detector comprises a photo diode.

### Claim 3

A circuit to amplify an electrical signal comprising:
a photo-detector to provide an input signal;
a first amplifier to receive an input signal from the photo-detector and to amplify the input signal to form an output signal, the first amplifier comprising an active input to receive the input signal and a non-active input; and
a second amplifier to force a constant voltage at the active and non-active input of the first amplifier, thereby negating a need for a dummy detector on the non-active input of the first amplifier;
further comprising a reference voltage, V reference, to provide a reference voltage to a non-inverting input of the second amplifier.

### Claim 4 (depends on 3)

The circuit of claim 3, wherein the second amplifier senses input common mode voltage of the first amplifier to determine an output signal to force a constant voltage at the active and non-active inputs of the first amplifier.

### Claim 5

A circuit to amplify an electrical signal comprising:
a photo-detector to provide an input signal;
a first amplifier to receive an input signal from the photo-detector and to amplify the input signal to form an output signal, the first amplifier comprising an active input to receive the input signal and a non-active input; and
a second amplifier to force a constant voltage at the active and non-active input of the first amplifier, thereby negating a need for a dummy detector on the non-active input of the first amplifier;
wherein the first amplifier is a transimpedance amplifier.

### Claim 6 (depends on 1)

The circuit of claim 1, wherein the output of the first amplifier is used in a laser-based device.

### Claim 7 (depends on 6)

The circuit of claim 6, wherein the laser-based device is a compact disc (CD) drive.

### Claim 8 (depends on 6)

The circuit of claim 6, wherein the laser-based device is a digital versatile disc (DVD) drive.

### Claim 9 (depends on 3)

The circuit of claim 3, wherein the photo-detector comprises a photo diode.

### Claim 10 (depends on 5)

The circuit of claim 5, wherein the photo-detector comprises a photo diode.

### Claim 11 (depends on 3)

The circuit of claim 3, wherein the output of the first amplifier is used in a laser-based device.

### Claim 12 (depends on 5)

The circuit of claim 5, wherein the output of the first amplifier is used in a laser-based device.

### Claim 13

a circuit comprising:
a photo-detector;
a transimpedance amplifier operably connected to the photo-detector; and
a second amplifier having a first input being the input common mode voltage of the transimpedance amplifier and a second input being a reference voltage, the output of the second amplifier providing feedback to the transimpedance amplifier.

### Claim 14 (depends on 12)

The circuit of claim 12, wherein the second amplifier drives the input common mode voltage of the transimpedance amplifier to an approximately constant level.

### Claim 15 (depends on 12)

The circuit of claim 12, wherein the output of the first amplifier is used in a laser-based device.

### Claim 16 (depends on 15)

The circuit of claim 15, wherein the laser-based device is a compact disc (CD) drive.

### Claim 17 (depends on 15)

The circuit of claim 15, wherein the laser-based device is a digital versatile disc (DVD) drive.