mm-wave op-amps for low distortion amplification with high OIP3/PDC ratio ≫ 100 at 2 GHz

We here report mm-wave amplifiers employing strong global negative feedback to provide very low intermodulation distortion, using an InP DHBT technology. The amplifiers, similar to operational amplifiers, use simple- or nested-Miller compensation and have 25 to 40 GHz feedback loop bandwidths. The large loop transmission at 2 GHz provides a large reduction of closed-loop distortion at this frequency. A simple-compensated amplifier with 24.8 GHz bandwidth and having 1013 mW dissipation showed 13.8 dB (S₂₁) gain and 50.2 dBm OIP3 at (1.950, 1.975 GHz). It is unconditionally stable from DC to 15 GHz, and stable in a 50 Omega system from DC to 50 GHz. A nested-compensated amplifier with 40 GHz bandwidth and having 993 mW dissipation showed 13.8 dB (S₂₁) gain and 42.8 dBm OIP3 at (1.950, 1.975 GHz). It is unconditionally stable from DC-20 GHz and stable in a 50 Omega system from DC to 50 GHz. These results represent _~ 4times increase in bandwidth for an op-amp of any kind, as well as _~ 3times betterment in OIP3/P_DC ratio at f_s = 2-3 GHz, when compared to state-of-the-art. We address considerations important to the application of negative feedback to mm-, microwave amplifiers, including the effects of interface impedances on stability, the effect of feedback upon return losses and noise figure, and the effect of frequency compensation and of feedback topology on closed-loop distortion.