Digital tuner for a communication receiver, typically an AM receiver

摘要

To provide a synthesized tuning frequency to control the local oscillator in a superheterodyne receiver, a frequency generating circuit includes a reference oscillator which provides a reference frequency which is frequency-divided to generate a plurality of divided sub-frequencies which, with respect to the reference frequency have at least a flank which is non-coincident with respect to corresponding flanks of other frequencies. These divided frequencies are added in an adder, the addition of which is controlled in accordance with a tuning command stored in a digital memory. Preferably, the adder is a NOR-gate to which selected frequencies are connected, selected by NAND-gates in accordance with a number provided by a digital tuning control and stored in the digital memory. The synthesized frequency is then used to provide an error control signal within a control loop connected to the local oscillator.