A Wide-band Receiver Front-end With Programmable Frequency Selective Input Matching

While wide-band wireless receivers are most often designed to match a constant, purely real antenna impedance of 50 Omega, in reality, the actual impedance of an antenna can vary widely at different operating frequencies and in different frequency environments. Additionally, the parasitics on the PCB, package bond wires and ESD pads inherently make the effective antenna impedance complex. This results in poor matching (S-11) at the receiver's input. The problem gets exacerbated in the higher end of the frequency band of the receiver. In this paper, we present an inductor-less, frequency translational resistive feedback receiver front-end, operating from 0.4 to 4 GHz. This receiver can be considered as a frequency translational version of a resistive feedback LNA. However unlike the LNA, the input match around the LO in the desired signal bandwidth is achieved by varying only the base-band components: a) by varying the global feedback resistors and b) varying the "complex" feedback resistors between the I and the Q paths. With these two degrees of freedom, the receiver designed in a 65-nm CMOS process, achieves at least -15 dBm S-11 in a signal bandwidth of 5 MHz at 4 GHz LO, with a negligible frequency shift of the receiver conversion gain. Simulation results show that the receiver front-end with two baseband gain stages has a gain of 36 dB and a worst-case noise figure of 3.5 dB.