Design techniques for tunable transresistance-C VHF bandpass filters

In this paper, a tunable wideband linear transresistance (R/sub m/) amplifier is proposed and analyzed. Using the tunable R/sub m/ amplifier, a new transresistance-capacitor (R/sub m/-C) differentiator is designed. Considering the intrinsic capacitances of the MOS transistors as filter elements, this R/sub m/-C configuration can he regarded as a very high frequency (VHF) bandpass biquadratic filter. The proposed biquad has a simple structure and thus occupies a small chip area and consumes little power. Moreover, higher-order VHF bandpass filters can be realized by directly cascading the biquads. Experimental results have successfully proven the capability of the proposed new filter implementation method in realizing VHF bandpass filters with the center frequency higher than 100 MHz when C/sub d/=1 pF. The deviations of the measured center frequency f/sub o/ and quality factor Q of the fabricated bandpass filter from the simulated results are less than 8%. The deviation of the center frequency can be post-tuned by adjusting the control voltages V/sub CN/ and V/sub CP/ of the tunable R/sub m/ amplifier. With 1 pF differentiating capacitor, the center frequency of the fabricated VHF R/sub m/-C bandpass filters can be tuned in a wide range larger than 30 MHz. The measured maximum signal level is 25 mV/sub rms/ and the dynamic range is 47 dB. The chip area is 0.05 mm/sup 2/ and power consumption is 5.05 mW with /spl plusmn/2.5 V power supply.<
>