Tunable linearity characteristics of a DC-3 GHz InP HBT active feedback amplifier

This paper reports on the linearity characteristics of a DC-3 GHz InP HBT amplifier with tunable active feedback. By electronically tuning the active feedback of the amplifier, a 3.5 dB improvement in IP3 over a broadband is obtained compared to a purely resistive feedback design with the same do power. At an optimal tuning bias, the amplifier achieves a DC-3 GHz bandwidth, 9.5 dB gain, a P/sub 1dB/ of 13.3 dBm, and an IP3 of 31 dBm at 1 GHz while consuming a modest 35 mA through a 5 V supply. An lP3/P/sub DC/ ratio of 6.6:1 is achieved which is more than double that obtained from an equivalent conventional resistive feedback design. The improved linearity is obtained with no substantial impact on the MMIC size or DC power consumption. Under large signal operation the amplifier was also found to obtain 14-15 dB improvement in C/IM3 ratio. This simple MMIC technique is a cost effective means for improving the performance of standard linear MMIC products.