High precision in situ tuning of monolithic continuous time leapfrog filters

The authors present an in situ method of tuning analog continuous time monolithic integrated circuit filters which achieves high precision when applied to leapfrog structures. The in situ method directly tunes selected subcircuits of the filter, so that neither accurate capacitor nor gain matching of circuit components is required. High precision is achieved by directly tuning highly isolated simple subsections of the filter. Two tuning methods are considered. First, lossless two-integrator loops are tuned by their oscillation frequencies. Secondly, single time constant circuits are tuned by observing magnitudes at cut-off frequencies. The tuning overhead of the in situ method is shown to be reasonable, much less than with the general programmable methods