Automatic frequency control apparatus and method therefor

• US 5,500,878 A
• Filed: 06/08/1994
• Issued: 03/19/1996
• Est. Priority Date: 06/08/1993
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: NEC Corporation
• Inventors: Iwasaki, Motoya
• Primary Examiner(s): Tse, Young T.
• Assistant Examiner(s): LUTHER, WILLIAM A
• Application Number:
  US08/255,367
• Time in Patent Office: 650 Days
• Field of Search: 375/330, 375/344, 375/261, 375/306, 375/311, 375/312, 375/357, 375/362, 375/324, 375/327, 375/326, 375/325, 455/164.1, 455/164.2, 329/325, 329/306-308, 329/360
• US Class Current: 375/344
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H03J 7/26 in which an automatic frequency control circuit is brought into action after the scanning action has been stopped

Abstract

An automatic frequency control apparatus includes a local oscillator, a quadrature detector, a frequency offset value estimation circuit, a demodulation circuit, a synchronization determination circuit, a memory, and an AFC circuit. The synchronization determination circuit determines reception synchronization on the basis of demodulated signals from the demodulation circuit to output a synchronization determination signal to the AFC circuit when reception synchronization is established and outputs the value to the AFC circuit. The apparatus also includes a power-on state detection circuit for outputting a detection signal to the AFC circuit. The AFC circuit determines the oscillation frequency of the local oscillator on the basis of the outputs from the above components. An automatic frequency control method is also disclosed.

Claims

1. An automatic frequency control apparatus comprising:

local oscillation means for outputting a local oscillation signal having an oscillation frequency controlled by a frequency control voltage;

quadrature detection means for quadrature-detecting a received signal using the local oscillation signal received from said local oscillation means;

frequency offset value estimation means for estimating a frequency offset value of the received signal from quadrature detection signals received from said quadrature detection means;

demodulation means for demodulating the quadrature detection signals received from said quadrature detection means and outputting demodulated signals;

synchronization determination means, coupled to said demodulation means, for determining reception synchronization according to said demodulated signals received from said demodulation means to output a synchronization determination signal when reception synchronization with a single received frequency is established;

frequency control means, coupled to said local oscillation means and to said synchronization determination means, for generating said frequency control voltage and outputting said frequency control voltage to said local oscillation means;

non-volatile memory means, coupled to said frequency control means, for storing a frequency control voltage received from said frequency control means obtained when said reception synchronization is established; and

said frequency control means being also coupled to said frequency offset value estimation means, for repeatedly changing a frequency control voltage to said local oscillation means according to the frequency offset value received from said frequency offset value estimation means until reception synchronization is established when no synchronization determination signal is output from said synchronization determination means, and controlling the oscillation frequency of said local oscillation means by the frequency control voltage read out from said non-volatile memory means when a power supply is turned on, said frequency control means effecting storing of the frequency control voltage into said memory means when the synchronization determination signal is output from said synchronization determination means to said frequency control means.

2. An apparatus according to claim 1, wherein a power from a power supply which is set in an ON state for a predetermined period of time in a predetermined cycle is intermittently supplied to said local oscillation means, said quadrature detection means, said frequency offset value estimation means, said demodulation means, said synchronization determination means, and said frequency control means, and said frequency control means reads out a frequency control voltage from said memory means each time the power supply is intermittently supplied, thereby controlling an oscillation frequency of said local oscillation means.

3. An apparatus according to claim 1, further comprising power-on state detection means for detecting a power-on state to output a detection signal to said frequency control means, and wherein said frequency control means reads out the frequency control voltage from said memory means when the detection signal is output from said power-on state detection means.

4. An automatic frequency control apparatus comprising:

local oscillation means for outputting a local oscillation signal having an oscillation frequency controlled by a frequency control voltage;

quadrature detection means for quadrature-detecting a received signal using the local oscillation signal from said local oscillation means;

frequency offset value estimation means for estimating a frequency offset value from quadrature detection signals received from said quadrature detection means;

demodulation means for demodulating the quadrature detection signals from said quadrature detection means;

synchronization determination means, coupled to said demodulation means, for determining reception synchronization according to demodulated signals received from said demodulation means to output a synchronization determination signal when reception synchronization with a single received frequency is established;

frequency control means, coupled to said local oscillation means and said synchronization determination means, for generating said frequency control voltage and outputting said frequency control voltage to said local oscillation means;

non-volatile memory means, coupled to said frequency control means, for storing a frequency control voltage obtained from said frequency control means when said reception synchronization is established; and

power-on state detection means for detecting a power-on state to output a detection signal;

said frequency control means being further coupled to said frequency offset value estimating means and said power-on state detection means, for repeatedly changing a frequency control voltage to be outputted to said local oscillation means according to the frequency offset value received from said frequency offset value estimation means until reception synchronization is established when no synchronization determination signal is output from said synchronization determination means,

said memory means storing a frequency control voltage at which reception synchronization is established when the synchronization determination signal is output from said synchronization determination means to said frequency control means, and

said frequency control means determining the oscillation frequency of said local oscillation means from a frequency control voltage read out from said memory means when the detection signal is output from said power-on state detection means.

5. A method of automatically controlling a frequency, comprising steps of:

quadrature-detecting a received signal using a local oscillation signal from local oscillation means having an oscillation frequency controlled by a frequency control signal;

estimating a frequency offset value of quadrature detection signals;

demodulating the quadrature detection signals and obtaining demodulated signals;

determining reception synchronization according to said demodulated signals;

generating said frequency control signal in a frequency control means and outputting said frequency control signal to said local oscillation means;

when no reception synchronization is established, repeatedly changing a frequency control voltage according to an estimated frequency offset value until reception synchronization is established;

when reception synchronization is established, storing a frequency control voltage obtained when the reception synchronization is established; and

when a power supply is turned on, controlling the oscillation frequency of said local oscillation means by the stored frequency control voltage, wherein the frequency control voltage obtained when the reception synchronization is established is stored in non-volatile storage means.

6. A method according to claim 5, further comprising the step of intermittently supplying a power from a power supply which is set in an ON state for a predetermined period of time in a predetermined cycle to a signal receiving system, and wherein the step of controlling the oscillation frequency comprises the step of controlling an oscillation frequency of said local oscillation means by the stored frequency control voltage each time the power supply is intermittently tuned on.