Receiver provided with an automatic frequency control loop.

摘要

Receiver (1-9) provided with a frequency control loop (2-6) for automatic fine tuning, consecutively incorporating a controllable oscillator (6) which is tunable in frequency by means of a variable capacitance diode (D), a mixer stage (2) to which the signal from the controllable oscillator (6) is applied for converting an RF receiver signal into an intermediate frequency signal, a frequency voltage converter (4) tuned to a fixed intermediate frequency for converting frequency deviations of the intermediate frequency signal relative to the fixed intermediate frequency into amplitude variations of the frequency voltage converter (4) output signal relative to a reference value, a control signal generating circuit (5) for deriving a control signal for the variable capacitance diode (D) of the controllable oscillator (6) from the output signal of the frequency voltage converter (4), which at least partly compensates the asymmetrical diode capacitance-voltage characteristic. In order to prevent unwanted side-tuning effects from occurring during this compensation, the frequency-dependent variation of the control signal for the variable capacitance diode (D) is to assume an asymmetrical S curve which is curved around the maximum values therein and which compensates the asymmetry in the diode capacitance variation.