Variable frequency passband circuit

Claim 1

A variable frequency passband circuit comprising: first and second bandpass filters (e.g., 1, 2) connected in a cascade fashion for forming a synthetic filter in a signal path, first and second oscillators (e.g., 6, 7) for respectively generating first and second frequency signals (e.g., f C1 , f C2 ) which can be varied by control signals applied thereto, first and second control means (e.g., 11, 12; 9, 10) for respectively producing said control signals to be applied to said first and second oscillators, a frequency signal generator (e.g., 8) for mixing said first and second frequency signals to produce a third frequency signal (e.g., f C3 ), a first mixer (e.g., 3) for mixing an input signal (e.g., f I1 ) to be applied to the circuit and said first frequency signal to produce a signal which is applied to said first bandpass filter, a second mixer (e.g., 4) for mixing an output signal of said first bandpass filter and said third frequency signal to produce a second frequency--converted input signal which is applied to said second bandpass filter, a third mixer (e.g., 5) for mixing an output of said second bandpass filter to produce a signal output of the circuit, and switching means (e.g., 113, 14) for connecting said first control means to said first oscillator and also said second control means to said second oscillator in a first operation mode, and alternatively connecting said first control means to said second oscillator and also said second control means to said first oscillator in a second operation mode.