Linearity enhancement technology for mixer in monolithic CMOS UHF RFID interrogator
Linearity requirements characterised by second-order intercept point (IP2) and third-order intercept point (IP3) are recapitulated for the proposed zero-IF receiver in accordance with ETSI and EPCglobal UHF radio frequency identification (RFID) protocols. To improve linearity of the downconversion mixer without noise penalty, the common mode intermodulation signal feedback through the bleeding current path and the inductively degenerated common source transconductance are adopted. The circuitry is demonstrated in 0.18 µm standard CMOS process. The average IP3 for 23 samples is of 15 dBm and the IP2 is boosted from 37 to 52 dBm while drawing 8.7 mA from a 3.3 V power supply. These results show that the mixer is also very promising for other high linearity RF receiver applications.
