Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Patent
1994-03-14
1996-06-04
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
4551601, 4551923, 4552341, 348735, H04B 116
Patent
active
055242898
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method and a circuit for an automatic, high precision frequency fine tuning with the help of an analog circuit, in which the frequency can be balanced, in an integrated circuit.
BACKGROUND
In the field of electronic signal processing, it is frequently necessary to accurately balance (align) frequencies or frequency-dependent circuits, for example, when adjusting tuners or balancing frequency generators.
Corresponding AFT (automatic fine tune) techniques are known from, for example, "Television Engineering Handbook", page 13.117, K. Blair Benson, McGraw-Hill Book Company. In this the phase shift in a parallel resonant circuit is evaluated.
FIG. 1 shows an appropriate block circuit diagram. An output signal 10 influenced by a tuning, for example, a television audio signal, is fed to a resonant circuit 11 and a first input of a phase detector 12. The resonant circuit is tuned to a desired frequency. The output signal from the resonant circuit 11 is fed to a second input of the phase detector. The output signal from the phase detector is filtered in a low-pass 13 and serves as regulating variable 14 for the tuning of the input signal 10. A circuit suitable for this is, for example, an FM demodulator 15 which can be tuned by a regulating variable and to which the regulating variable 14 and a signal 16 for demodulating are fed.
In this particular application, however, only a tuning accuracy of about 150 kHz can be achieved with the state of the art. Apart from that, such known AFT circuits cannot be fully integrated. For example, two connections to an integrated circuit are required for an external resonant circuit.
A further known solution consists of counting digitally the frequency to be tuned and to re-adjusting it accordingly. However, the expenditure on circuitry and the corresponding chip area in an integrated circuit required herefor are high. The current consumption for such a digital AFT circuit is also relatively high.
SUMMARY OF THE INVENTION
It is the object of the invention to specify a method for automatic, high precision frequency fine tuning with little expenditure on circuitry and current consumption in integrated circuits.
In principle, the method according to the invention is that, for the purpose of automatic, high precision frequency fine tuning, for example, of a certain television channel, for an analog circuit, in which the frequency can be balanced, within an integrated circuit, at least one regulating variable for the frequency-balanceable analog circuit is formed and stored depending on a high precision reference frequency, the value of said variable is also influenced by a reference circuit section within the integrated circuit, and that for the fine tuning, successively, different operating modes are switched on.
It is a further object of the invention to specify a circuit for the method according to the invention.
In principle, the circuit according to the invention is provided with an analog circuit 23, 33, in which the frequency can be balanced by means of a regulating variable, with a feeding point for a high precision reference frequency f.sub.ch, a first, second and third change-over switch, a first T1, second T2 and third T3 automatic gain control amplifier, a first CL and a second CH comparator, a summer (adder) 21, and with an internal capacitor C.sub.int, whereby: of the first T1 and the second T2 automatic gain control amplifiers and the first CL and the second CH comparators; automatic gain control amplifier T1 in a normal mode; compensation voltage V.sub.of, is fed to a first input 252 of the second automatic gain control amplifier T2 in calibration mode; V.sub.ref and a threshold voltage V.sub.th, is fed to a first input 254 of the first comparator CL and a summation voltage, being the sum of the reference voltage V.sub.ref and the threshold voltage V.sub.th, is fed to a first input 253 of the second comparator CH in a measuring mode; to a first input N of the third change-over switch in the normal mode; to a third input C of the third ch
REFERENCES:
patent: 4245351 (1981-01-01), Tults
patent: 4358791 (1982-11-01), French
patent: 4977613 (1990-12-01), Holcomb, Sr. et al.
Koblitz Rudolf
Rieger Martin
Roth Sabine
Eisenzopf Reinhard J.
Emanuel Peter M.
To Doris
Tripoli Joseph S.
Wein Frederick A.
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