| 摘要 |
PROBLEM TO BE SOLVED: To automatically cancel an offset voltage by allowing an automatic zero control circuit to close a cancellation loop while the offset voltage is measured and stored in standby mode. SOLUTION: An automatic zero amplifier AZ26 maintains the voltage at a node 62 by removing the effect of the offset voltage in all the rest of the standby mode at VREF1. The continuance of the standby mode is equal to at least the time needed for the automatic zero amplifier AZ26 to match the voltage at the node 62 with VREF1. The automatic zero amplifier AZ26 cancels both a positive and a negative offset voltage. When the input voltage of a power control amplifier GM32 is different, an offset voltage is present. In the standby mode, the automatic zero amplifier AZ26 cancels the offset voltage by measuring the voltage of the not-inverted input part of the power control amplifier GM32 of the power control amplifier GM32. Consequently, the voltage at the node 62 approximates to VREF1.
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