A broadband automatic gain control amplifier for the Square Kilometer Array

In this paper, a low-power broadband automatic-gain-control (AGC) amplifier targeted for use in the Square Kilometer Array (SKA) is presented. The AGC is composed of an input power-match circuit, a linear-in-dB output variable gain amplifier (VGA), a power detector (PD), an error amplifier, a comparator and a loop filter. The input stage is power matched to 100 Ω differential source impedance, achieves an input reflection coefficient of less than -15.6 dB and maximum noise figure of 2.6 dB from 0.5 GHz to 2.0 GHz. The VGA has a variable gain range of 29 dB and -3 dB bandwidth of 4 GHz. The square-law relationship between output current and gate-source voltage characteristics of a MOS transistor working in the strong inversion region is used for power detection. The -3 dB bandwidth of the AGC amplifier is 2.65 GHz with and 3.6 GHz without the power-match circuit. The input operating range of the AGC is from -50 dBm to -20 dBm. The design is based on a commercial 65 nm CMOS technology with a 1 V power supply. The total power consumption of the AGC is 6 mW of which 4.5 mW is consumed by the input-match circuit which is not needed when the AGC is integrated in the SKA receiver.