Design of a CMOS High Dynamic Range Automatic Gain Control System for Telecommand Applications

Automatic Gain Control circuits are closed loop control systems that are widely used in telecommand applications for avionics systems and other receivers to maintain a constant output signal level despite variation of signal amplitude at its input. The design of an analogue Automatic Gain Control System employing AMS-0.35 μm CMOS technology at 3.3V supply voltage is shown in this study, for a frequency of 10.7 MHz with a desired output level at -10dBm for an input dynamic range of -85dBm to +3dBm. The system consists of 50Ω matched single-ended input and output variable gain amplifier whose gain is automatically adjusted with the control voltage generated in the feedback loop. The feedback loop consists of a low power CMOS RF power detector along with a control voltage generator. The RF Power detector consists of an RMS power detector and a sequence of limiting amplifiers operating as a logarithmic detector. The RF power detector has a dynamic range of -60dBm ~-10dBm. The control voltage generator used in this system is a square-law based consisting of a single transistor, thereby saving the chip space to a great extent. The AGC gain ranges from 71.4dB ~-9.43dB with an output level accuracy of ± 3.5dB. The proposed AGC system has a very high input dynamic range.