GB1600393A

GB1600393A - Correcting oscillator output frequency for temperature variations

Info

Publication number: GB1600393A
Application number: GB3965777A
Authority: GB
Original assignee: Thales Research and Technology UK Ltd; Racal Research Ltd
Current assignee: Thales Research and Technology UK Ltd; Racal Research Ltd
Priority date: 1977-09-23
Filing date: 1977-09-23
Publication date: 1981-10-14
Also published as: DE2841240A1

Description

(54) CORRECTING OSCILLATOR OUTPUT FREQUENCY FOR TEMPERATURE VARIATIONS (71) We, RACAL RESEARCH LI MITED, a British Company, of Western Road, Bracknell, Berkshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to electrical circuit arrangments for correcting for the effect of temperature changes of the output crystal oscillator circuits.

According to the invention, there is provided an electrical circuit arrangement for correcting for the effect of temperature changes on the output frequency of a crystal oscillator, comprising storage means arranged to store a plurality of correction signals, one for each incremental value of temperature and each predetermined in accordance with a known relationship between ambient temperature of the oscillator or part thereof and output frequency of the oscillator, transducing means for measuring the said ambient temperature of the oscillator of the part thereof, means responsive to the output of the transducing means for reading out from the storage means the correction signal corresponding to the measured ambient temperature, a frequency synthesizer driven by the oscillator, and frequency correction circuitry operative in response to each read-out correction signal to apply corresponding adjustment to the frequency synthesizer so that the latter produces a resultant frequency which is substantially independent of the effect of ambient temperature variations on the oscillator or on the said part thereof.

An electrical circuit arrangement embodying the invention, and for correcting the frequency of an oscillator susceptible to errors due to temperature changes, will now be described, by way of example, with reference to the accompanying diagrammatic drawing in which: Figure 1 is a curve illustrating a characteristic of the oscillator; and Figure 2 is a block diagram showing the oscillator and the correcting circuit arrangement.

As shown in the drawing, a crystal oscillator 10 is assumed to have a frequency ambient temperature characteristic as shown in Figure 1, and the circuit arrangement now to be described is arranged to correct for the effect of temperature on the oscillator frequency, so as to produce an output frequency which is substantially independent of the effect of temperature.

Associated with the oscillator 10 is a temperature-sensitive transducer 12 which measures the temperature of the oscillator 10 and produces a corresponding output signal, normally an electrical signal on a line 14. Reference to Figure 1 indicates that for every value of the control signal on line 14 (that is, for every value of temperature represented by this control signal) there will be a corresponding frequency of the oscillator 10 - and therefore a corresponding deviation from a desired predetermined value. The circuit arrangment therefore includes a read-only memory (ROM) 16 in which are stored, for each incremental value of the control signal on line 14 (that is, for each incremental value of temperature), a signal (which would normally be stored as a digital signal) representing the corresponding frequency correction.

The control signals on the line 14 are connected to control a decoding unit 18 which in turn controls the reading circuit for the ROM 16.

Therefore, for each value of the control signal 14, the unit 18 causes the ROM 16 to read out a corresponding frequency correction on a line 20. The line 20 is connected to a frequency correcting unit 22 which applies a correction, in dependence on the value of the signal on the line 20, to the oscillator output 10, and the corrected output is fed out on an output line 24.

The frequency on the line 24 is therefore substantially independent of temperature.

The correcting unit 22 comprises a frequency synthesizer driven by the output from the crystal oscillator 10 and adjusted by the signals on the line 20.

The correction signals stored in the ROM would normally be stored as digital signals but this is not necessarily essential.

The temperature sensitive transducer 12 may comprise any suitable device such as a temperature sensitive resistive element, for example a thermistor. Instead, however, it could comprise another crystal oscillator whose output frequency would (in accordance with its previously known frequency temperature characteristics) be dependent on temperature.

Using the correction circuit described, it is not necessary for the usual controlledtemperature oven to be provided for accurately holding the temperature of the oscillator 10 constant.

WHAT WE CLAIM IS: 1. An electrical circuit arrangement for correcting for the effect of temperature changes on the output frequency of a crystal oscillator, comprising storage means arranged to store a plurality of correction signals, one for each incremental value of temperature and each predetermined in accordance with a known relationship between ambient temperature of the oscillator or part thereof and output frequency of the oscillator, transducing means for measuring the said ambient temperature of the oscillator of the part thereof, means responsive to the output of the transducing means for reading out from the storage means the correction signal corresponding to the measured ambient temperature, a frequency synthesizer driven by the oscillator, and frequency correction circuitry operative in response to each read-out correction signal to apply corresponding adjustment to the frequency synthesizer so that the latter produces a resultant frequency which is substantially independent of the effect of ambient temperature variations on the oscillator or on the said part thereof.

2. An arrangement according to claim 1, in which the transducing means is a further crystal oscillator.

3. An electrical circuit arrangement, substantially as described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the signal on the line 20, to the oscillator output 10, and the corrected output is fed out on an output line 24. The frequency on the line 24 is therefore substantially independent of temperature. The correcting unit 22 comprises a frequency synthesizer driven by the output from the crystal oscillator 10 and adjusted by the signals on the line 20. The correction signals stored in the ROM would normally be stored as digital signals but this is not necessarily essential. The temperature sensitive transducer 12 may comprise any suitable device such as a temperature sensitive resistive element, for example a thermistor. Instead, however, it could comprise another crystal oscillator whose output frequency would (in accordance with its previously known frequency temperature characteristics) be dependent on temperature. Using the correction circuit described, it is not necessary for the usual controlledtemperature oven to be provided for accurately holding the temperature of the oscillator 10 constant. WHAT WE CLAIM IS:

1. An electrical circuit arrangement for correcting for the effect of temperature changes on the output frequency of a crystal oscillator, comprising storage means arranged to store a plurality of correction signals, one for each incremental value of temperature and each predetermined in accordance with a known relationship between ambient temperature of the oscillator or part thereof and output frequency of the oscillator, transducing means for measuring the said ambient temperature of the oscillator of the part thereof, means responsive to the output of the transducing means for reading out from the storage means the correction signal corresponding to the measured ambient temperature, a frequency synthesizer driven by the oscillator, and frequency correction circuitry operative in response to each read-out correction signal to apply corresponding adjustment to the frequency synthesizer so that the latter produces a resultant frequency which is substantially independent of the effect of ambient temperature variations on the oscillator or on the said part thereof.