An Analog-Controlled Attenuation Network for a 4–240-GHz InP Variable-Gain Amplifier

This article presents a broadband variable-gain amplifier (VGA) using an analog-controlled input attenuation network (IAN) in a distributed amplifier (DA). The IAN adjusts the bias condition of newly implemented diode-connected transistors to change the attenuation constant of the input transmission line, therefore, controlling the contribution of each gain stage to the total VGA’s gain across a wide bandwidth. A 4–240-GHz indium phosphide VGA prototype demonstrates an average small-signal gain of 11 dB from 4 to 230 GHz and 7.8 dB at 240 GHz with return losses of less than −10 dB up to 200 GHz. The gain control bandwidth is from 4 to 170 GHz, with a measured gain control range from 8.9 to 4.7 dB. The saturated output power exceeds 14 dBm up to 200 GHz; the output third-order intercept point (OIP3) averages at 23 dBm up to 67 GHz; and the output 1-dB compression point (OP1dB) averages at 12 dBm up to 170 GHz. Across gain states at 90 GHz, the OIP3 and OP1dB are maintained within 0.1 and 2.5 dB variation, respectively. In addition, the VGA generates a constant output power of 11 dBm while accommodating an input power range of up to 12 dB. The chip occupies an area of $1.3\times 0.8$ mm² and consumes 54 mA bias current from a 6.6-V supply.