Highly linear attenuator and mixer for wide band TOR in CMOS

In this thesis work, a highly linear passive attenuator and mixer were designed to be used in a wide-band Transmission Observation Receiver (TOR). The TOR is a low IF receiver that accepts RF frequencies from 2GHz to 7GHz, and produces corresponding IF bandwidths of 280MHz to 990MHz respectively, using low side LO injection. The dynamic range is maximized by using passive topologies for both the attenuator and the mixer. The system is dealing with different power levels ranging from -30dBm to +1dBm, and hence, a programmable digital step attenuator is used to attenuate large signals. It provides a maximum of 31dB of attenuation in 1dB steps. Different mixer architectures were compared, including CMOS mixer, mixer with dummy switches and quadrature mixer. Also, the performance of the mixer in both voltage mode and current mode was investigated. A double balanced passive mixer in voltage mode, with dummy switches was adopted in the final system since it proved to be the best in terms of meeting the requirements. The work was carried out in Ericsson in Lund, using Cadence, 65nm process. The circuit is true differential and it uses a supply voltage of 1.2V. The final results show a spurious free dynamic range of higher than 85dBc, minimum in band IIP3 of +15dBm , maximum IIP3 of +50dBm and a worst input return loss of less than -10dB. The amplitude and phase precision over the observation bandwidth were quite good, a worst phase error of less than 3 degrees was recorded and an amplitude error of 0.5dB