A variable-gain image-reject down-converter for 5-6 GHz WLAN applications

A monolithic down-converter for 5-6 GHz WLAN applications was designed using a 46-GHz-f_T silicon bipolar process. The circuit consists of a variable-gain low noise amplifier and a double-balanced mixer. In high-gain mode, the down-converter exhibits a 3 dB noise figure and a 23 dB power gain, with an input compression point of -20 dBm. In low-gain mode, the circuit provides a 7.5 dB noise figure and a power gain of 12 dB, with an input compression point of -10 dBm. Moreover, an excellent image rejection ratio is achieved by means of monolithic passive notch filters, still maintaining a noise figure lower than 4 dB.