Patent ID: 8073419

Claim:
A front-end circuit with coherent tunable filters, comprising: a first filter, with a first tunable intermediate frequency, for filtering a received signal; an amplifier, coupled to the first filter, for amplifying an output of the first filter; and a second filter, with a second tunable intermediate frequency and coupled to the amplifier, for filtering an output of the amplifier; wherein the amplifier is placed between the first filter and the second filter, and the first and second intermediate frequencies have a coherent-tuning relation with each other, wherein the first filter, the second filter, and the amplifier form an integrated circuit, and the integrated circuit comprises: an input end, an output end, and a ground end; a first transistor, coupled to the input end, the output end, and the ground end; a variable capacitor, coupled to the output end; and a variable inductor, coupled to the output end; wherein the first transistor comprises a parasitic capacitor placed between the input end and the output end.