An improved Q-tuning scheme and a fully symmetric OTA

An improved tuning scheme for continuous-time high-Q biquad filters is proposed. An improvement over the existing implementation of the modified-LMS Q-tuning scheme is combined with frequency tuning using PLL. The scheme has less area overhead, consumes less power and is more robust to offsets in the building blocks without compromising the accuracy achieved previously. A new architecture for a pseudo-differential fully-symmetric high frequency transconductor is also proposed. It combines CMFF and CMFB to achieve a faster common mode response. A bandpass filter with center frequency 100 MHz and Q of 20 is built using the proposed OTA. The proposed tuning scheme is used to tune the filter. The circuit is fabricated in standard CMOS 0.5μm technology and the experimental results show that the Q tuning error is around 1%.