A programmable 3-V CMOS rail-to-rail opamp with gain boosting for driving heavy resistive loads

This paper describes a programmable 3-V CMOS rail-to-rail opamp with gain boosting. The unity-gain frequency can be programmed from 0.5 to 4 MHz, for a load of 50 pF, by changing the supply current from 55 to 390 μA. The g_m-control of the input stage functions regardless of its operating region, whether it is weak or strong inversion. This allows an optimal frequency compensation over the total programming range. The opamp features a low-voltage gain-boosting technique which provides a high gain of about 120 dB, even for loads of 50 Ω. The opamp has been designed in a 1 μm BiCMOS process