| 摘要 |
A linear differential amplifier is fabricated in CMOS and combined with digital control so that an analog input signal can be converted to a selected output polarity. When the amplifier output is coupled directly to the inverting input the noninverting input provides a unity gain voltage follower configuration. To create a unity gain signal inverter, a matched pair of resistors is employed. One resistor is coupled between the amplifier output and the inverting input while the other is coupled between the analog signal input and the inverting input. In operation digital control is employed in switching between the two configurations. The sense of the differential amplifier is reversed when switching between configurations thereby to provide a substantial reduction of the effect of offset potential. To fully compensate the offset pootential, a capacitor is periodically coupled across the amplifier input to charge it to the offset potential. Then an equal value capacitor is connected in parallel thus having the potential and the combination coupled to the noninverting amplifier input during the time when the inverting configuration is in operation. The same amplifier offset is present in both configurations, but in opposite polarities, and therefore produces equal, but opposite VREF switching through digital control.
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