High frequency receiving apparatus

A high frequency receiving apparatus comprising:

• a first mixer for mixing a first local oscillation signal with a high frequency input signal to obtain a first intermediate frequency signal;
• a first local oscillation device for controlling a frequency of a first oscillator with a PLL system on the basis of an oscillation frequency of a first reference solid-state oscillation element, and for sending said first local oscillation signal into said first mixer;
• a second mixer for mixing a second local oscillation signal with said first intermediate frequency signal to obtain a second intermediate frequency signal;
• a second local oscillation device for controlling a frequency of a second oscillator with a PLL system on the basis of an oscillation frequency of a second reference solid-state oscillation element and for sending said second local oscillation signal to said second mixer;
• a detection oscillator for generating an oscillation signal for picture synchronous detection;
• a picture synchronous detector for producing a detection output having a specific phase difference from said oscillation signal of said detection oscillator based upon said second intermediate frequency signal;
• a phase comparator for comparing a phase difference between said second intermediate frequency signal and said oscillation signal of said detection oscillator;
• a variable capacitive element equivalently connected in parallel to said second reference solid-state oscillation element of said second local oscillation device for converting a voltage change into a capacitance change;
• and
• a voltage feedback device for applying an output voltage of said phase comparator to said variable capacitive element.

A method for synchronous detection of high frequency signals, comprising the steps of:

• receiving a high frequency input signal;
• providing a local oscillator for sending a local oscillation signal to a mixer;
• controlling a frequency of said local oscillator with a PLL system on the basis of an oscillation frequency of a reference solid-state oscillation element;
• connecting a variable capacitive element equivalently in parallel to said reference solid-state oscillation element for converting a voltage change to a capacitance change to control said reference solid-state oscillation element;
• mixing said local oscillation signal with said high frequency input signal by said mixer to obtain an intermediate frequency signal;
• generating an oscillation signal by a detection oscillator for picture synchronous detection based on said intermediate frequency signal;
• comparing a phase difference between said intermediate frequency signal and said oscillation signal of said detection oscillator;
• producing a detection output based on a specific phase difference between said oscillation signal of said detection oscillator and said intermediate frequency signal;
• and
• applying an output voltage of the phase comparison to said variable capacitive element to change a capacitance of said variable capacitive element such that said intermediate frequency converges within an oscillation frequency range of said detection oscillator.