A miniaturized L-band 4-bit differential VGA using resistance-selectable bridged-T attenuators for a fine tuning of gain

A miniaturized L-band 4-bit differential variable gain amplifier (VGA) has been developed to realize a fine tuning of gain for use in the active phased array modules. It incorporates a resistance-selectable bridged-T attenuator into the design of the series feedback circuit of the differential amplifier and achieves 4-bit, 16-states gain variations by switching on and off the bridging-resistances alternatively. An L-band 4-bit VGA has achieved a gain from 3.9 to 5.4dB with 0.1dB step, a rms gain error of 0.024dB, a phase imbalance of less than 8° for all gain states, a noise figure of less than 4dB, and an IIP₃ of greater than -7dBm at 1 GHz.