R. Griffith et al., A 1-V BICMOS RAIL-TO-RAIL AMPLIFIER WITH N-CHANNEL DEPLETION MODE INPUT STAGE, IEEE journal of solid-state circuits, 32(12), 1997, pp. 2012-2022
A BiCMOS rail-to-rail operational amplifier capable of operating from
supply voltages as low as 1 V is presented. The folded cascode input s
tage 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-end
ed conversion network employs a low-voltage base current cancellation
technique which provides high input stage voltage gain from a l-V supp
ly 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, Thi
s circuit topology enables the amplifier to achieve a 4-MHz bandwidth
with 60 degrees of phase margin, The output voltage can swing to withi
n 50 mV of each supply rail. An ''on-demand'' base current boost techn
ique will be presented which can provide up to 50 mA of output drive c
apability from a 5-V supply, yet consumes only a few microamps when th
e output is in the quiescent state, A low voltage level shift techniqu
e will be described which uses an n-channel depletion mode source foll
ower to provide isolation between the input and output stages.