An Enhanced Adaptive Q-Tuning Scheme for a 100-MHz Fully Symmetric OTA-Based Bandpass Filter

A tuning scheme for continuous-time highbiquad filters is presented. An improvement over the existing implementation of the modified-LMS -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 and 0-tuning scheme does not require the -tuning loop to be slower than the 0-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 0.5technology, with a bandpass filter of center frequency 100 MHz and of 20, along with the proposed tuning scheme. The measured -tuning error is around 1%. Expected and experimental results are in good agreement.