A wideband downconverter and analog baseband for radio astronomy applications

A wideband downconverter and analog baseband that has been fabricated using a 0.25μm Silicon-On-Sapphire (SOS) CMOS process is reported. The signal path includes a wideband input amplifier, I/Q mixers, baseband anti-aliasing filters and differential ADC drivers. The LO input is divided by two on chip to generate quadrature phases. The LO buffers include a digitally tunable load in order to optimize the down conversion performance. The baseband gain is digitally controllable over a range of 13.6 dB, and the typical passband conversion gain is 26 dB. The downconverter works with RF inputs from below 500 MHz to above 1.8 GHz, and the baseband 3dB bandwidth is greater than 120 MHz. Baseband filtering ensures 40 dB SNR for an ADC with sample rates as low as 550 MS/s.