Weak inversion MOS varactors for 0.5 V analog integrated filters

This work proposes a weak-inversion MOS capacitor-based varactor, tuned through the body voltage, for the realization of tunable filters at supply voltages down to 0.5 V. Weak inversion operation results in a distributed series resistance and a model is derived to accurately calculate this frequency dependent resistance. The model matches well with experimental results from test devices in a 0.18 μm CMOS technology. Channel segmentation is used to simulate the varactor. Use of the varactor is demonstrated in the design of tunable filters and good agreement is obtained between simulated and measured performance.