Automatic frequency control oscillation circuit

An automatic frequency control oscillation circuit, comprising:

• a voltage-controlled oscillator for producing an oscillation signal whose frequency is controlled by a primary control voltage, said primary control voltage being derived from a secondary control voltage;
• a phase comparator for detecting a phase difference between a frequency-divided signal derived from the oscillation signal, and a reference signal thereby generating a phase difference signal;
• and
• a control circuit for generating a secondary control voltage to reduce a time-dependent change in the phase difference signal and synchronize the oscillation signal with the reference signal;
• said control circuit comprising:
• means for monitoring and comparing time-dependent change in the phase difference signal with a predetermined initial phase difference;
• and
• means for determining said secondary control voltage when the time-dependent change in the phase difference signal is detected to be equal to or smaller than said predetermined initial phase difference;
• analog-to-digital converter for converting the phase difference signal from an analog form into a digital phase difference signal;
• a high-speed processor for generating a digital control voltage in response to the digital phase difference signal;
• and
• digital-to-analog converter for converting the digital control voltage into an analog control voltage;
• a flash read-only memory for storing a digital first control voltage and said predetermined initial phase difference, wherein said high-speed processor comprises means for storing a stored control value from said flash read-only memory when the time-dependent change in the phase difference signal is detected for the first time to be equal to or smaller than said predetermined initial phase difference, and thereafter reading the stored control value into said digital-to-analog converter.

An automatic frequency control oscillation circuit, comprising:

• a voltage-controlled oscillator for producing an oscillation signal whose frequency is controlled by a primary control voltage;
• a phase comparator for detecting a phase difference between a frequency-divided signal derived from said oscillation signal and a reference signal thereby generating a phase difference signal;
• and
• a control circuit for generating a secondary control voltage to reduce a time-varying phase difference signal and synchronize said oscillation signal with the reference signal;
• said control circuit comprising:
• means for storing a predetermined initial phase difference;
• means for monitoring and comparing said time-varying phase difference signal with said predetermined initial phase difference;
• means for determining said secondary control voltage when the time-varying phase difference signal is detected to be equal to or smaller than said initial phase difference;
• and
• means for deriving said primary control voltage from said secondary control voltage and delivering said primary control voltage to said voltage-controlled oscillator.

A method of controlling an oscillation signal of an automatic frequency control oscillation circuit having a voltage-controlled oscillator for producing an oscillation signal whose frequency is controlled by a primary control voltage, a phase comparator for detecting a phase difference between a frequency-divided signal derived from the oscillation signal and a reference signal thereby generating a phase difference signal, and a control circuit for generating a secondary control voltage to reduce a time-dependent change in the phase difference signal to synchronize the oscillation signal with the reference signal, said method comprising the steps of:

• establishing an initial phase difference as a threshold for the time-dependent change in the phase difference signal;
• comparing the time-dependent change in the phase difference signal with said initial phase difference;
• determining said secondary control voltage when the time-dependent change in the phase difference signal is detected to be equal to or smaller than said initial phase difference;
• and
• establishing said primary control voltage from said secondary control voltage.