Continuous-Time Active Filters Based On OTAs And OAs

Fully Integrated Continuous-Time Active Filters is a frontier topic in microelectronics, circuits and systems. It is applied widely in communication, electronic measurement, instrumentation and cybernation. Analog Filter is an important element of analog integrated circuits. The structure generation and circuit design method for analog filter can be widely applied in large-scale integrated circuit design, which is of important application value and reference value. The academic circles and industrial community are widely interesting in the Operational Transconductance Amplifier(OTA), because of its high working frequency, fast voltage conversion rate, good electronic control, facilitative integration. The active filters which are made of OTAs and Operational Amplifiers(OAs) have excellent performance and significant application and theoretical value. Active filters research is a subject with great potential.Firstly in this paper, the OA active filters are discussed. The basic principles of OA active filters composed passive components such as resister and capacitor are introduced. Following this the OTA theory and its application are analyzed. The representative circuits composed of active devices OTA which applied in the analog signal processing are summarized. The low-order OTA-C filter's basic theory is analyzed, then a novel filter design method is proposed. The new second-order filter with tri- inputs and single-output can achieve multi-function as Low-Pass(LP),High-Pass(HP),All-Pass(AP), Band-Pass (BP) and Band-stop(BS).Based on the tri-inputs and single-output filter, we design a novel multi-function filter with single-input and four-outputs. This novel second-order filter also can get the LP, HP, BP and BS functions. The results show that this filter has good multifunction filtering effects.Secondly, the design principles and methods for second-order multi-function active filters are introduced. Two novel voltage-mode OTA-OA multi-function active filters are proposed. The first circuit is only used two single-output OTAs and two OAs. It realized the HP and BP functions. Another tri-inputs and tri-outputs model of second-order voltage-mode multi-function filter also only used two single-output OTAs and two OAs. With different combination of the three inputs and three outputs, it can achieve sorts of functions such as a LP, HP, BP, BS and AP functions respective.By simulating the second-order OTA-OA multifunctional filters with PSPICE, it shows that the simulation results are in good agreement with the theoretical-results, verifies the correctness of the design method and indicates that the two types of multi-function filters can realize the low-pass, band-pass, band-stop and high-stop function. The sensitivity analysis shows that the novel two proposed filters have low sensitivities with respect to the circuit active parameters. The proposed circuits designed without passive components such as resistors and capacitors. The new multi-function filters are characterized with fewer components, occupying less chip area and having simple structure, are more suitable for integration. These two filters have a better application value.