CMOS input stage circuits and related methods
地域：
TX
TX Austin
摘要
Embodiments of improved CMOS input stage circuits and related methods are provided herein to maintain a near constant transconductance across an entire common-mode input voltage range of the input stage. One embodiment includes a pair of NMOS input transistors and a pair of PMOS input transistors, each coupled to receive a differential input voltages at their gate terminals; a current source coupled to source terminals of the pair of PMOS input transistors and configured to generate a current; a current steering circuit configured to steer the current to the pair of NMOS input transistors and/or to the pair of PMOS input transistors, depending on whether a common mode input voltage (CMV) is greater than, less than, or substantially equal to a cross-over voltage; and a current stealing circuit configured to reduce the current when the CMV is substantially equal to the cross-over voltage.
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combine to produce a net transconductance of gmn,cross+gmp,cross=√{square root over (2)}gm. Thus, as the common-mode input voltage is swept, CMOS input stage 200 still provides inconsistent gm when transitioning across the Vcross boundary region. The gm inconsistency at the boundary region causes the unity-gain bandwidth (UGB) to change over the common-mode input voltage range, which is an undesirable behavior in amplifier designs. The variable UGB, in turn, causes another undesirable phenomenon, as set forth below.
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