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.