Log-domain low-pass biquads with independent and continuous tuning of main parameters

This paper presents two new Externally Linear Internally Nonlinear (ELIN) low-pass second order filters. The first topology was derived from a standard state-variable biquad by using a LIN-ELIN transformation. The resulting structure was improved in order to simplify its implementation. Both biquads allow for orthogonal tuning of their Ho, ω0 and Q. They can be tuned continuously by varying only DC bias currents. Simulation results demonstrate the analytical analysis.

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