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

A BiCMOS rail-to-rail operational amplifier capable of operating from supply voltages as low as 1 V is presented. The folded cascode input stage uses an nMOS depletion mode differential pair to provide rail to-rail common mode voltage range while typically requiring only 40 fA of input bias current, The bipolar transistor differential-to-single-ended conversion network employs a low-voltage base current cancellation technique which provides high input stage voltage gain from a l-V supply yet allows a 3-V/mu s slew rate capability, The bipolar transistor output stage uses a low-voltage translinear loop which maintains a low impedance signal path to the output common emitter power devices, This circuit topology enables the amplifier to achieve a 4-MHz bandwidth with 60 degrees of phase margin, The output voltage can swing to within 50 mV of each supply rail. An ''on-demand'' base current boost technique will be presented which can provide up to 50 mA of output drive capability from a 5-V supply, yet consumes only a few microamps when the output is in the quiescent state, A low voltage level shift technique will be described which uses an n-channel depletion mode source follower to provide isolation between the input and output stages.