Abstract：To improve the complex structure, high power consumption and low precision of on-chip Gm-C filter automatic frequency tuning circuits, an accurate constanttransconductance bias circuit was proposed. The cutoff frequency of the filter was stabilized by making the transconductance of the transconductance transistor identically equal to an off-chip high precision resistor. The operation theory was derived, and the filter and transconductor were designed. The circuit was applied to the 9th order low pass filter for wireless sensor chips, and the simulation was conducted. This chip was implemented in SMIC 0.18 μm 18 V 1P6M CMOS technology and the low pass filter was realized by the synthesis of passive LC filter prototype. The test results show that there is only a difference of 1％ between the cutoff frequency and the designed value and the inband ripple is less than 0.8 dB. The inputreferred noise is less than 25 nV／Hz with a power consumption of 1.6 mW. The results meet the requirements of wireless sensor chips.
2011, Vol. 32 
