A broadband Variable Gain Amplifier for the Square Kilometer Array

In this paper, an inductorless broadband linear-in-dB Variable-Gain Amplifier (VGA) circuit for use in the Square Kilometer Array (SKA) is presented. A two-transistor topology, which realizes a linear-in-dB function, is used to design a differential VGA. The VGA is both input and output power matched to 100Ω differential sources and loads. The design is fabricated in ST 65nm CMOS technology with a 1V power supply. Measurement results show that the VGA has a 25dB variable gain range, input P1dB of -25dBm to -32dBm with control voltage ranging from 0.5V to 1.0V, and is designed to work in a frequency range from 0.7GHz to 1.4GHz, which is the frequency range of the mid-band SKA receiver. The total power consumption of the VGA is 1mW with another 6mW consumed by an input-match circuit and 1mW consumed by an output buffer circuit.