By Using Darlington Topology Improvement of In-Band Gain for the Log Domain Filters

By using Darlington topology, an alternative circuit is proposed to overcome the in-band gain problem for the log domain circuits. This idea is applied to a third order elliptic filter synthesized in the log domain. Simulations are performed in order to compare the performances of ideal transistors with infinite forward gain, CBIC-R transistors and CBIC-R transistors connected in Darlington topology. The AC response of the Darlington connected transistors gives better performance in terms of in-band gain. THD and noise performances are also investigated. In addition, the circuit is driven by a signal at the filter's corner frequency, i.e. f=100 kHz, for the time domain analysis. The results are discussed