A switch controlled resistor based CMOS PGA with DC offset cancellation for WSN RF chip

In this paper, a programmable gain amplifier (PGA) for wireless sensor network (WSN) is proposed and implemented using 0.18 μm CMOS process. A fully differential feedback configuration is adopted, and the variable gains are achieved by switch controlled resistor (SCR) network. DC feedback technique is also utilized to eliminate the DC offset. SCR network layout design is essential to maintain the accuracy of the gain value under process variations. Local and global common centroid symmetric layout techniques are applied to ensure the matching of the resistors in SCR network. Post-simulation results show that the PGA has 0 dB~60 dB variable gain range and 1 dB gain resolution; the minimum DC attenuation is 20d B over whole gain range; the pass-band range is 10.8 Hz~20.15 MHz under most gain configurations; output swing is 1.4 V; and the PGA consumes 3.7 mA current with 1.8 V supply voltage. Chip measurement results show that the PGA can achieve 2.23 dB~56.66 dB variable gain range after minor bias voltage adjustment; and the total current it consumes is about 5.2 mA.