Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1995-11-17
1998-08-25
Saras, Steven J.
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345100, G09G 336
Patent
active
057987475
ABSTRACT:
In a sample and hold amplifier of an analog video display column driver, an operational amplifier output is disconnected from a hold capacitor during the sampling and hold phases. The operational amplifier settling time is not involved in the sampling onto the hold capacitor. The operational amplifier is powered down until the scan line is written to the display. During the sampling and hold modes, no power is consumed. The analog input signal is sampled onto hold and differential capacitors with the operational amplifier disabled. Sampling speed is high since the operational amplifier is not in the loop, and therefore settling need not occur. After one scan line is sampled, a line activation command closes switches and enables the operational column drive amplifiers, thereby enabling the feedback loop of the operational amplifiers. In the preferred embodiment, switches disconnect the differential inputs of the operational amplifier from the hold capacitor and differential capacitor, respectively, when the amplifier is not enabled. In an alternate embodiment, the negative terminals of the hold and differential capacitors are directly connected to the negative and positive differential inputs of the operational amplifier, respectively. In a second alternate embodiment, there are two separate sample and hold circuits, and yet only a single column drive circuit.
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Lewis David L.
National Semiconductor Corporation
Saras Steven J.
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