In the paper, a general topology of continuous-time Active-RC filter is presented. The model includes all possible Active-RC filter structures as particular cases and allows us to analyze them using a unified algebraic formalism. This makes it suitable for use in computeraided analysis and design of Active-RC filters. By its construction, the model takes into account the finite DC gain and the finite bandwidth as well as non-zero output resistance of operational amplifiers. Filters with ideal OPAMPs can be treated as particular cases. Sensitivity and noise analysis of Active-RC filters is also performed in the proposed general setting. The correctness of the model is verified by comparison with SPICE simulation.
In the paper, a feedforward linearization method for differential-pair operational transconductance ampliﬁer (OTA) is discussed. The proposed technique is developed using simple differential pair transconductors and linear reference resistor. The concept leads not only to very efficient linearization ofa transfer characteristic oft he OTA but also others the possibility of effﬀective phase compensation. Due to this, the circuit can be used in applications requiring precise phase response (e.g. ﬁlters). SPICE simulations show that for the circuit working with a ±1.25V power supply, total harmonic distortion (THD) at 0.8Vpp is less then 0.1% in comparison to 10.2% without linearization. Moreover, the input voltage range ofline ar operation is increased. Power consumption oft he overall circuit is 0.94mW. The 3rd order elliptic ﬁlter example has been designed and simulated. It turns out that the proposed compensation scheme signiﬁcantly improves the performance of the ﬁlter at higher frequencies.