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An enhanced adaptive Q-tuning scheme for a 100-MHz fully symmetric OTA-based bandpass filter

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3 Author(s)
P. Kallam ; Maxim Integrated Products, Chelmsford, MA, USA ; E. Sanchez-Sinencio ; A. I. Karsilayan

A tuning scheme for continuous-time high-Q biquad filters is presented. An improvement over the existing implementation of the modified-LMS Q-tuning scheme is proposed and efficiently combined with the frequency tuning based on phase-locked loops. The proposed scheme takes much less area without compromising the accuracy achieved previously. The proposed unified Q- and f0-tuning scheme does not require the Q-tuning loop to be slower than the f0-tuning loop. The optimal case is to have equal speeds for both loops. Also, a low-voltage pseudo-differential operational transconductance amplifier with inherent common-mode feedforward is introduced. The structure is fully symmetric and suitable for high-frequency applications. An experimental test chip is fabricated in standard CMOS 0.5-μm technology, with a bandpass filter of center frequency 100 MHz and Q of 20, along with the proposed tuning scheme. The measured Q-tuning error is around 1%. Expected and experimental results are in good agreement.

Published in:

IEEE Journal of Solid-State Circuits  (Volume:38 ,  Issue: 4 )