Circuit arrangement for compensating temperature-dependent frequency variations of a crystal-controlled oscillator
AssigneeSocieta Italiana Telecomunicazioni Siemens S.p.A.
InventorsManlio Saba, Roberto Szocs
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Abstract
A subcarrier frequency-modulated with a message signal is heterodyned with a carrier from a crystal-controlled oscillator in a mixer whose output is fed to a filter eliminating one of the resulting sidebands. In order to compensate temperature-dependent fluctuations of the carrier frequency, a function generator produces a corrective signal which is added to the message signal in the input of the frequency modulator traversed by the subcarrier. The corrective signal varies as a quadratic or a cubic function of temperature, depending upon the type of cut used on the quartz crystal controlling the carrier oscillator, with a polarity determined by which of the two sidebands is passed by the filter.
Claims7
In a message-transmitting system using frequency modulation, in combination:
- a crystal-controlled oscillator generating a carrier of a frequency subject to temperature-dependent fluctuations;
- a frequency modulator having a first input for receiving a subcarrier and a second input for receiving a message signal to be modulated upon said subcarrier;
- a function generator in the vicinity of said oscillator emitting a corrective signal of a magnitude varying as a function of temperature related to the temperature dependence of said fluctuations;
- summing means connected to said function generator and to a source of said message signal for supplying the latter together with said corrective signal to said second input whereby said subcarrier is frequency-modulated by the sum of said message and corrective signals;
- mixer means with input connections to said oscillator and to said modulator for heterodyning said carrier with the frequency-modulated subcarrier to produce a pair of sidebands respectively representing the sum and the difference of said carrier and subcarrier, the temperature-dependent fluctuations of said carrier being substantially compensated by the corrective modulation of said subcarrier in one of said sidebands;
- and
- filter means downstream of said mixer means for suppressing the other of said sidebands.
Dependencies are inferred from the claim text.