| 摘要 |
For varying the filter frequencies in an integrator-filter circuit for filtering a push-pull signal by at least two integrator signal filters (31, 32, 33) having integrator elements (1), whose filter frequencies are adjustable by control currents (In,1, In,2) applied to the integrator elements (1), the integrator-filter circuit includes a reference integrator filter (38) having at least two integrator elements (1) constructed in an identical technique as the other integrator elements (1). This reference integrator filter, when tuned to the frequency of a test signal applied thereto, shifts the phase of the test signal by a defined value, and is arranged subsequent to a phase comparator (39) which also receives the test signal, so that a correction signal is derived from the output signal of the phase comparator (39), in dependence upon this correction signal. The control currents (In,1, In,2) applied to the integrator elements (1) of the reference integrator filter (38) and the integrator signal filters (31, 32, 33) are generated and in response to the control currents the reference integrator filter (38) is tuned to the frequency of the test signal applied thereto, in that the integrator signal filters (31, 32, 33) are tuned to rated frequencies in dependence upon the correction signal when the reference integrator filter (38) is tuned exclusively in response to the two control currents to a reference frequency test signal applied thereto. For tuning the integrator signal filters (31, 32, 33) at filter frequencies deviating by a predeterminable detuning value from the rated frequencies, at least a switching control current is superimposable on the control currents applied to the reference integrator filter (38), this switching control current being dimensioned in such a way that, when tuning the reference integrator filter (38) to the test signal by the correction signal, this test signal causes the integrator signal filters (31, 32, 33) to tune to frequencies which deviate by the detuning value from their rated frequencies.
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