Circuit for producing a contrast voltage signal for a liquid crystal display which uses a differential comparator, capacitors, transmission gates and feedback to reduce quiescent current
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United States of America Patent
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Jul 18, 2000
Grant Date -
N/A
app pub date -
Mar 20, 1998
filing date -
Mar 20, 1998
priority date (Note) -
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Abstract
A circuit (100) for produces an LCD contrast voltage signal (VLCD) for a low power MCU-controlled application. The reference voltage (VREF) for a switched mode power supply circuit (210) is supplied by a circuit comprising: logic control circuitry (110) for receiving MCU commands, a counter (120), a digital-to-analog converter (130), and a transmission gates (140, 150) and capacitors (160, 180) for generating the SMPS reference voltage (VREF), and a comparator to set off a recharge cycle whenever the capacitors' voltage difference is more than a pre-set offset voltage. This circuit has lower quiescent power consumption since, in idle cycle, only the comparator (200) consumes quiescent current which can be less than 1 .mu.A.
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