Codesign of Mixer-VGA Downconverter Blocks

Two radio frequency integrated circuit (RFIC) downconverters are presented, each consisting of an active mixer and a variable gain amplifier (VGA). The downconverter blocks (DCBs) have identical mixing stages but different VGA topologies. The mixers use a commutating switching network and a low-noise RF transconductance stage to reduce the system noise figure (NF). VGA gain control in one DCB (DCB-1) is done using a current-steering approach, while the second DCB (DCB-2) employs a transistor-based attenuator. Both RFICs were designed and fabricated using a standard 130-nm CMOS process and they were tested over the RF band covering 1-6 GHz and at an IF of 140 MHz. Measurements show that the conversion gain (CG) of DCB-1 ranges from 9.6 to 25.3 dB, and for DCB-2, the CG ranges from 10.7 to 23.7 dB. The minimum double-sideband NF for both the downconverters is 3.8 dB but their maximum NFs are different: 1) 14.2 dB for DCB-1 and 2) 11.5 dB for DCB-2.