Design of bipolar differential opamps with unity gain bandwidth up to 23 GHz

Abstract

We compare the RF performance of fully differential opamps developed in 0.25 mum SiGe complementary (pnp/npn) technology and 0.13 mum SiGe BiCMOS (with npn only). Using the same compensation technique, the frequency response of these opamps is analyzed with emphasis on the phase margin (PM) and gain margin (GM). The pnp/npn opamp has advantage in unity gain bandwidth (UGB) and current consumption in comparison to the 0.13 mum BiCMOS design (supply voltage of 4 V). For the pnp/npn opamp a 23 GHz UGB can be achieved with PM of 57 degrees. In case of the pnp/npn opamp the supply voltage can be reduced to 3 V using a new topology with resistor for tail current. The optimized RF pnp/npn opamp allows the design of a differential line driver (50 Ohm) with 24 GHz bandwidth and a second order 2 GHz biquad bandpass filter.