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A 0.5-V fully integrated R-MOSFET-C filter with low power, good linearity, and wide frequency tunability is demonstrated. It relies upon the operational transconductance amplifier using the cross-forward common-mode cancellation and the linear sub-threshold R-MOSFET resistor-both employ subthreshold operation of the transistors. A fifth-order Chebyshev low-pass filter using regular transistors with a 0.5-V threshold voltage in a 0.18-μm triple-well CMOS process is implemented for a 0.5-V supply. The filter's bandwidth can be tuned from 91 to 268 kHz, which is almost a 3-to-1 tuning ratio. At a nominal bandwidth of 135 kHz automatically set by the on-chip PLL circuit, the dynamic range is at 61.0 dB for 1% total harmonic distortion, while the spurious-free dynamic range under two-tone signals is at 53.7 dB. The total current and power consumptions including bias circuits are 1.2 mA and 0.6 mW, respectively.
Date of Publication: Nov. 2012