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Browse Prior Art Database

Base Line Follower

IP.com Disclosure Number: IPCOM000095324D
Original Publication Date: 1965-Nov-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 70K

Publishing Venue

IBM

Related People

Bartz, M: AUTHOR

Abstract

Tapped delay line 10 integrates the analog video and generates a dynamic average signal. This is applied to the transistor T1 base of the base line follower circuit 15. The latter operates on the dynamic average and generates a clipping level which is applied to an input of voltage discriminator 11. This generates an output which is at one of two voltage levels. Such depends upon whether the center tapped video from 10 is more positive or negative than the clipping level applied from 15. If the center tapped video is more positive, a black condition exists. If more negative, a white condition exists.

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Base Line Follower

Tapped delay line 10 integrates the analog video and generates a dynamic average signal. This is applied to the transistor T1 base of the base line follower circuit 15. The latter operates on the dynamic average and generates a clipping level which is applied to an input of voltage discriminator 11. This generates an output which is at one of two voltage levels. Such depends upon whether the center tapped video from 10 is more positive or negative than the clipping level applied from 15. If the center tapped video is more positive, a black condition exists. If more negative, a white condition exists.

A comparison can be made between the center-tapped video and the dynamic average to distinguish white from black. However, there is a problem which arises when making this comparison. This is when the video output has been relatively constant, either white or black, for a period of time longer than the length of the delay line. Under this condition, the dynamic average becomes almost equal to the center tapped video. Since there is a considerable amount of electrical noise on the center-tapped video signal, it is not possible under such an arrangement to make an accurate comparison when the dynamic average is approximately equal to the center-tapped video. Hence, the dynamic average must be operated upon before it can be used as a clipping level. The problem can be solved by shifting the dynamic average up and away from the noise when in white, i. e., an A level signal, and down and away from the black level noise when in black, i. e., a B level signal. This shifting function is performed by 15. The output of 11, which is at a positive level when the video is black and at a negative level when white, is fed back to 15 to indicate the way to shift the dynamic average.

Circuit 15 also performs an additional function. When the video goes from black to white with a very gradual fall time, the B level tends to follow along with the video. Under this condition, it is possible for the cente...