Differential amplifier using voltage level shifting to achieve rail-to-rail input capability at very low power supply voltage

摘要

A differential amplifier coupled between sources of a high supply voltage (VHH) and a low supply voltage (VLL) contains a pair of differential portions (30 and 32), that are used to amplify a differential input signal (VI1 and VI2). One of the differential portions is turned on when the common-mode voltage of the input signal is in a portion of the supply range extending up to the high supply voltage. The other is turned on when the input common-mode voltage is in a portion of the supply range extending down to the low supply voltage. A level-shift circuit (38, 40, 42, 44, and 46) selectively raises or lowers the voltages at input points (P1, P2, P3, and P4) to the differential portions. The level shifts extend the conductive ranges of the differential portions. This enables the amplifier to eahcieve rail-to-rail input capability down to 1 volt or slightlty less for the power supply voltage.