Source: Proc. IEEE Internation Symposium on Circuits and Systems, Vol. 3, pp643-646, June, 1998.
Abstract:
The stability of a continuous-time state variable filter is analyzed using the Routh-Hurwitz criterion. This criterion assesses stability by indicating the number of poles that lie in the right-half plane. The filter is examined separately with integrators implemented with an ORA-L and a current amplifier. Both amplifier types are characterized by a dominant-pole frequency response, and the stability of each implementation is compared. HSPICE simulations confirm the theoretical analyses, which indicate that the bandwidth of the ORAs and current amplifiers must be much larger than the desired frequency of operation to ensure stability. Since the analyses assume a dominant-pole response, all higher-order poles of the actual amplifier must also be much greater than the unity-gain frequency to minimize excess phase.
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