A 1 V BiCMOS rail-to-rail amplifier with n-channel depletion-mode input-stage

This amplifier is fabricated on a SMARTMOS/sup TM/ flow with depletion-mode nMOS, vertical p-n-p, and high-frequency n-p-n transistors. Most techniques for achieving rail-to-rail input stage performance concentrate on the use of complementary bipolar or enhancement MOSFET devices to allow the amplifier common-mode range to include both supply rails. These techniques require a minimum supply voltage of 1.8 V for bipolar and 3 V for CMOS to allow a transition from sensing common mode voltages at ground when the p-n-p or pMOS pair is active, to sensing common-mode voltages at the positive supply when the n-p-n or nMOS pair is active. This amplifier uses a single pair of depletion-mode nMOS devices to allow low-voltage, rail-to-rail operation.