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D.C. RESTORE WITHOUT FREQUENCY DEGRADATION

IP.com Disclosure Number: IPCOM000026125D
Original Publication Date: 1990-Jun-30
Included in the Prior Art Database: 2004-Apr-05
Document File: 4 page(s) / 107K

Publishing Venue

Xerox Disclosure Journal

Abstract

In electronic input scanners, the information portion of the video signal from the image sensor "rides" on a D. C. signal (a D.C. offset) that varies from device to device. The D.C. offset must be removed from the signal before the signal passes through an AID converter. Generally, as shown in Figure 1, a capacitor is connected to the non-inverting input of an operational amplifier in series with the video signal, which limits the frequency response of the circuit significantly. The high speed operational amplifier required by the video signal is also very expensive.

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Page 1 of 4

XEROX DISCLOSURE JOURNAL

D.C. RESTORE WITHOUT Proposed Classification FREQUENCY DEGRADATION U.S. C1.358/000 Donald J. Gusmano Int. C1. H04n

- 1 Fig. Restore D.C. -74

Videoln 0 0 Video Out

D.C. Fig- 3

Offset

CurrentSink 0

Fig- 2 I

-

XEROX DISCLOSURE JOURNAL - Vol. 15, No. 3 May/June 1990 169

[This page contains 1 picture or other non-text object]

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D.C. RESTORE WITHOUT FREQUENCY DEGRADATION(Cont'd)

In electronic input scanners, the information portion of the video signal from the image sensor "rides" on a D. C. signal (a D.C. offset) that varies from device to device. The D.C. offset must be removed from the signal before the signal passes through an AID converter. Generally, as shown in Figure 1, a capacitor is connected to the non-inverting input of an operational amplifier in series with the video signal, which limits the frequency response of the circuit significantly. The high speed operational amplifier required by the video signal is also very expensive.

A new circuit is proposed, as shown in Figure 2, that performs the D.C. offset removal function by generating a current I so as to produce a voltage VDC across a resistor R, where VDC equals the D.C. offset value.

Thus,

VIDEO OUT = VIDEO IN - VDC

To accomplish this result, and as shown in Figure 3, the D.C. offset is directed to the inverting input of an operational amplifier to produce a voltage V1, so that

V1= -VDC OFFSET

V1 is then used to generate current 11, where:

I1 = (-VBE l-Vl)/R

and

I1 =I2

Therefore:

VIDEO OUT = VIDEO IN - (R X((-VBEl-V1)/R)-VBE...