A 4–240-GHz InP Variable-Gain Amplifier Using an Analog-Controlled Input Attenuation Network

This paper presents the design of a broadband variable-gain amplifier (VGA) using a new analog-controlled input attenuation network for a distributed amplifier (DA). The input attenuation network implements diode-connected HBTs along the DA’s input transmission line to continuously adjust its attenuation rate, thus, signal amplitudes at inputs and outputs of DA’s gain stages. By adjusting the diodes’ bias conditions, the individual stages’ contributions to the DA’s total gain are controlled, determining the number of effective stages for continuous gain variation across a wide bandwidth. A 4–240-GHz indium phosphide VGA is designed and characterized to validate the concept. The fabricated VGA provides an average gain of 11 dB from 4 to 230 GHz and 7.8 dB at 240 GHz. The continuous gain control range is measured from 8.9 to 4.7 dB across frequencies from 70 to 170 GHz. The input and output return losses are below -10 dB up to 200 GHz. The VGA generates an average power of 16 dBm and 1-dB compression point of 12 dBm up to 170 GHz. The output power is > 14 dBm up to 200 GHz and > 10 dBm up to 230 GHz. The chip occupies an area of 1.3 × 0.8 mm² and consumes 54 mA bias current from a 6.6-V supply.