Some design methods of OTA-C and CCII-RC filters

OTA-C filters and CCII-RC filters using the CCII as the transconductance amplifier are discussed in a unified context. Benefitting from each other in this way, more OTA-C and CCII-RC filter topologies may be generated. In particular, a class of CCII transconductance amplifier (CCIITA) based filter structures may be obtained from well-developed OTA-filters by simple one-to-one substitution of CCIITAs for OTAs in OTA-C filters. The signal flow graph method of OTA-C and CCII-RC filter synthesis is also investigated in the paper with the emphasis that with different structures the same transfer function may be realized not only as the voltage gain, but other types as well, for example current gain. The modified signal flow graphs of general transfer functions given in the paper are more straightforward for circuit realization. The adjoint network method which has been used to transform voltage amplifier filters to current amplifier counterparts is extended to transform transconductance amplifier filters. Both the indirect SFG transformation method and the direct element replacement method are proposed. These methods may be readily used to produce more filter configurations from the known equivalents. The simple transconductor is also accommodated into these methods and a number of new transconductor-grounded capacitor filters are obtained