Design of common-mode self-tuned fully integrated continuous-time transconductance-capacitance filters

Continuous-time (c-t) filters require tuning of such parameters as their pole frequencies and Q's that strongly depend on process and temperature variation. Since the accuracy of the traditional tuning method, Master-Salve (M-S), is limited by matching errors between the model (M) and the main filter (S), direct- or self-tuning (ST) of the main filter free from the matching errors would result in an improved accuracy. However, for most practical applications ST is not possible since the tuning signal would interfere with the signals processed by the filter.; Applying the reference signal to two single-ended filters in the common-mode (CM) and the processed signals in the differential-mode (DM) has successfully solved this problem. Taking the sum of the two outputs the processed signals cancel and the reference is recovered. Conversely, taking the difference of the two outputs the processed signal is recovered free from the reference. It can be proved that the filter's transfer functions for DM and CM are nearly the same. Thereby, by applying the recovered reference signals to frequency- and Q-tuning schemes an accurate filter tuning is achieved.; The new tuning method--common-mode self-tuning (CM-ST) has been theoretically analyzed, and practically verified by designing and fabricating a bipolar filter chip. For the first time a true self-tuned active continuous-time filter, i.e., the filter that is being tuned while simultaneously processing the main signal, has been implemented. The filter is tunable from 10-60 MHz and it is equipped with automatic frequency- and Q-tuning schemes. The results of chip measurements confirm the theoretical assumptions that the accuracy of the CM-ST method is better than the classical M-S.; The synthesis of a {dollar}gsb{lcub}m{rcub}{dollar}-C filter without using a common-mode feedback (CMF) to control the dc output voltage creates another important accomplishment. It is performed by loading the integrating nodes with 1/{dollar}gsb{lcub}m{rcub}{dollar} resistors that become a part of the filter transfer function. Again, measurements confirm that this approach is a viable filter synthesis method that eliminates difficult-to-design at high-frequency CMF circuit.; Finally, a theoretical insight has been given to many important problems of c-t filter design such as accuracy analysis for CM-ST and MS methods, analysis of errors in frequency- and Q-tuning systems, generalized frequency-response of a CMF circuit, and many others.