A.F.C. system for broad-band FM receiver
First Claim
1. An automatic frequency control system for performing correction of a frequency error of a center frequency of a frequency-modulated intermediate frequency signal with respect to a predetermined intermediate frequency value such as to hold the magnitude of said frequency error within a predetermined frequency error range, for a frequency modulation receiver system including local oscillator circuit means for producing a local oscillator signal and a frequency mixer coupled to receive said local oscillator signal for producing said frequency-modulated intermediate frequency signal, said automatic frequency control system comprising:
- control means;
frequency comparison means controlled by said control means to selectively operate in a first status for comparing said center frequency of said intermediate frequency signal with an upper limit frequency of said frequency error range and in a second status for comparing said center frequency of said intermediate frequency signal with a lower limit of said frequency error range, and for producing a frequency comparison signal indicative of results of said frequency comparisons;
first and second latch memory means controlled by said control means to store said frequency comparison signal as data indicative of the relationship between said center frequency of said intermediate frequency signal and said upper and lower limit frequencies, and;
frequency adjustment means controlled by said control means for adjusting said local oscillator frequency;
said control means operating, following said frequency comparison operation, to determine whether said data stored in said first and second latch memory means indicates that said center frequency of said intermediate frequency signal is within said frequency error range, and operating when said center frequency is determined to be within said frequency error range to execute successively alternating comparisons of said center frequency of said intermediate frequency signal with said upper and lower limits respectively by said frequency comparison means, and to store the level of said frequency comparison signal in said first latch memory means following a comparison of said center frequency of said intermediate frequency signal with said upper limit frequency and to store the level of said frequency comparison signal in said second latch memory means following a comparison of said center frequency of said intermediate frequency signal with said lower limit frequency, said control means further operating, when said center frequency of said intermediate frequency signal is determined to be outside said frequency error range as indicated by said data stored in said first and second latch memory means, to control said frequency adjustment means such as to adjust said local oscillator frequency to bring said center frequency of said intermediate frequency signal within said frequency error range.
1 Assignment
0 Petitions
Accused Products
Abstract
An A.F.C. control system for reception of wide-band F.M. transmission such as satellite transmissions, in which a center frequency of an F.M. I.F. signal is repetitively and alternately compared with an upper and a lower frequency limit value so long as the center frequency lies between these values, with the results of the comparisons being respectively stored in two latch memories, whose contents thereby indicate any error of the center frequency relative to the frequency limits. Any departure of the center frequency from between the limits is corrected by successive frequency shifts of the local oscillator frequency, with the results of correction being indicated by the latch memory contents and with the number of frequency shifts being determined accordingly.
-
Citations
14 Claims
-
1. An automatic frequency control system for performing correction of a frequency error of a center frequency of a frequency-modulated intermediate frequency signal with respect to a predetermined intermediate frequency value such as to hold the magnitude of said frequency error within a predetermined frequency error range, for a frequency modulation receiver system including local oscillator circuit means for producing a local oscillator signal and a frequency mixer coupled to receive said local oscillator signal for producing said frequency-modulated intermediate frequency signal, said automatic frequency control system comprising:
-
control means; frequency comparison means controlled by said control means to selectively operate in a first status for comparing said center frequency of said intermediate frequency signal with an upper limit frequency of said frequency error range and in a second status for comparing said center frequency of said intermediate frequency signal with a lower limit of said frequency error range, and for producing a frequency comparison signal indicative of results of said frequency comparisons; first and second latch memory means controlled by said control means to store said frequency comparison signal as data indicative of the relationship between said center frequency of said intermediate frequency signal and said upper and lower limit frequencies, and; frequency adjustment means controlled by said control means for adjusting said local oscillator frequency; said control means operating, following said frequency comparison operation, to determine whether said data stored in said first and second latch memory means indicates that said center frequency of said intermediate frequency signal is within said frequency error range, and operating when said center frequency is determined to be within said frequency error range to execute successively alternating comparisons of said center frequency of said intermediate frequency signal with said upper and lower limits respectively by said frequency comparison means, and to store the level of said frequency comparison signal in said first latch memory means following a comparison of said center frequency of said intermediate frequency signal with said upper limit frequency and to store the level of said frequency comparison signal in said second latch memory means following a comparison of said center frequency of said intermediate frequency signal with said lower limit frequency, said control means further operating, when said center frequency of said intermediate frequency signal is determined to be outside said frequency error range as indicated by said data stored in said first and second latch memory means, to control said frequency adjustment means such as to adjust said local oscillator frequency to bring said center frequency of said intermediate frequency signal within said frequency error range. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13)
-
-
12. An automatic frequency control system for performing correction of a frequency error of a center frequency of a frequency-modulated intermediate frequency signal with respect to a predetermined intermediate frequency value such as to hold the magnitude of said frequency error within a predetermined frequency error range, for a frequency modulation receiver system including local oscillator circuit means for producing a local oscillator signal and a mixer coupled to receive said local oscillator signal for producing said frequency-modulated intermediate frequency signal, said automatic frequency control system comprising:
-
control means; frequency comparison means controlled by said control means to selectively operate in a first status for comparing said center frequency of said intermediate frequency signal with an upper limit frequency of said frequency error range and in a second status for comparing said center frequency of said intermediate frequency signal with a lower limit of said frequency error range, and for producing a frequency comparison signal indicative of results of said frequency comparisons; first and second latch memory means controlled by said control means to store said frequency comparison signal as data indicative of the relationship between said center frequency of said intermediate frequency signal and said upper and lower limit frequencies; frequency adjustment means controlled by said control means for adjusting said local oscillator frequency; said control means operating, following said frequency comparison operation, to determine whether said data stored in said first and second latch memory means indicates that said center frequency of said intermediate frequency signal is within said frequency error range, and operating when said center frequency is determined to be within said frequency error range to execute successively alternating comparisons of said center frequency of said intermediate frequency signal with said upper and lower limits respectively by said frequency comparison means, and to store the level of said frequency comparison signal in said first latch memory means following each comparison of said center frequency of said intermediate frequency signal with said upper limit frequency and to store the level of said frequency comparison signal in said second latch memory means following each comparison of said center frequency of said intermediate frequency signal with said lower limit frequency, said control means further acting, when said center frequency of said intermediate frequency signal is determined to be outside said frequency error range as indicated by said data stored in said first and second latch memory means, to control said frequency adjustment means such as to adjust said local oscillator frequency to bring said center frequency of said intermediate frequency signal within said frequency error range, and; delay control means for establishing a predetermined data transfer delay time for transfer of said stored data from said first and second latch memory means to be analyzed by said control means, said delay control means being responsive to said tuning command signal for setting said data transfer time delay to a first value thereof; wherein, in response to a subsequent change in said stored data in said latch memory means indicating that said center frequency of said intermediate frequency signal has moved within said frequency error range, said delay control means operates to set said data transfer delay time to a second value thereof which is substantially longer than said first value thereof and to thereafter maintain said data transfer delay time at said second value thereof. - View Dependent Claims (14)
-
Specification