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AUTOBIASING AND DYNAMIC RANGE MAXIMIZATION IN A GREYSCALE DIFFERENTIAL AMPLIFIER

IP.com Disclosure Number: IPCOM000042669D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Le, T: AUTHOR

Abstract

The dynamic range of a differential greyscale video amplifier is maximized and autobiasing is achieved by the use of a simulation of the maximum voltage swing state to control the amplifier's current source. In Fig. 1, a signal proportional to the maximum state (Fig. 2) is needed to control current source transistor Q3. Such control is desirable in order to achieve autobiasing and to maximize the dynamic range of the amplifier. Since the amplifier is greyscale, only a portion of the current I0 is steered from side to side at any given time and the occurrence of the maximum state cannot be predicted. The outputs V01 and V02, therefore, cannot be monitored directly. Autobiasing and dynamic range maximization can still be achieved if a simulation is used.

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AUTOBIASING AND DYNAMIC RANGE MAXIMIZATION IN A GREYSCALE DIFFERENTIAL AMPLIFIER

The dynamic range of a differential greyscale video amplifier is maximized and autobiasing is achieved by the use of a simulation of the maximum voltage swing state to control the amplifier's current source. In Fig. 1, a signal proportional to the maximum state (Fig. 2) is needed to control current source transistor Q3. Such control is desirable in order to achieve autobiasing and to maximize the dynamic range of the amplifier. Since the amplifier is greyscale, only a portion of the current I0 is steered from side to side at any given time and the occurrence of the maximum state cannot be predicted. The outputs V01 and V02, therefore, cannot be monitored directly. Autobiasing and dynamic range maximization can still be achieved if a simulation is used. Transistor Q4 and resistors NRL and NRE simulate a low power version of the outputs V01 and V02 when transistor Q1 or Q2 is near saturation (maximum state). The constant, N, is a non-zero integer. Since the base voltage of transistor Q4 is the same as that of Q3, the current through Q4 is Is = IO : N. This current flowing through NRL produces voltage V05, a simulation of voltages V01 and V02 when Q1 or Q2 is near saturation. Voltage V05 is fed back to comparator A1. The feedback loop sets the current Is (and thus IO) to optimize V05 (and thus, V01 and V02), maintaining the proper bias with supply conditions and maximizing the output dy...