Dielectric resonator oscillators with digital temperature compensation

• US 4,712,078 A
• Filed: 03/27/1985
• Issued: 12/08/1987
• Est. Priority Date: 03/27/1985
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Webster, Richard T., Roberts, George A., Stiglitz, Martin R., Slobodnik, Andrew J. Jr.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US06/716,729
• Time in Patent Office: 986 Days
• Field of Search: 331/96, 331/99, 331/107 SL, 331/117 D, 331/176
• US Class Current: 331/99
• CPC Class Codes: H03L 1/021 of generators comprising distributed capacitance and inductance

Abstract

A digital compensation circuit for improving the temperature stability of dielectric resonator oscillators is disclosed. A temperature sensor indicates a measure of ambient temperature which is correlated with an amount of phase shift necessary to compensate for frequency drift in a dielectric resonator oscillator. The correlation is made using a correction table or correction function which is determined empirically in a calibration process. The necessary phase shift is then supplied via a voltage controlled phase shifter. This phase shifter is part of the RF oscillation loop which also includes an amplifier, directional coupler and dielectric resonator filter (including microstrip).

Claims

1. In combination with a dielectric resonator oscillator including a dielectric resonator which oscillates to produce a radio frequency (RF) clock signal which has phase shift characteristics corresponding to a resonant frequency, said resonant frequency having a frequency drift with changes in ambient temperature, said dielectric resonator oscillator including microstrip lines which are electrically connected in series with a directional coupler, said microstrip lines being placed in proximity to said dielectric resonator which couples said radio frequency clock signal between said microstrip lines thus closing the oscillator loop, a temperature compensation feedback circuit which reduces temperature sensitivity and frequency drift in said clock signal, said temperature compensation feedback circuit comprising:

a temperature sensing means which produces an output signal which indicates the ambient temperature, said output signal being a temperature reading;

a correlation menas which is electrically connected in series with said temperature sensing means, and which receives said temperature reading from said temperature sensing means, and produces an output signal which indicates an amount of phase adjustment which is necessary in said clock signal to eliminate frequency drift due to changes in the ambient temperature;

a digital-to-analog converter which is electrically connected in series with said correlation means, and which receives said output signal from said correlation means, and converts it into an analog siganl;

a phase shifter which is electrically connected in series with said digital-to-analog converter, and which receives said clock signal and said analog signal from said digital-to-analog converter, said phase shifter also being electrically connected with said microstrip lines, and outputting an adjusted clock signal which compensates for the phase shift in the dielectric resonator due to changes in the ambient temperature; and

an ampliifer which is electrically connected in series between said phase shifter and said directional coupler, and which produces an output by receiving and amplifying said adjusted clock signal from said phase shifter.

2. A temperature compensation feedback circuit, as defined in claim 1, including a calibration means which is placed in proximity with said dielectric resonator and said microstrip lines, and which electrically connects with said directional coupler and said temperature sensing means, said calibration means performs a calibration by varying the ambient temperature around said dielectric resonator, measuring said frequency in said lock signal, and producing an appropriate amount of phase adjustment in the clock signal required to correct for drift in said frequency for corresponding ambient temperature readings, said calibration means being detachable from said compensation feedback circuit wen the calibration is complete, said calibration means obtaining data during calibration which is used to generate a correction table, said correction table being a correlation between variations of ambient temperature around the dielectric resonator and the amount of phase adjustment in the clock signal resulting therefrom.

3. A temperature compensation feedback circuit, as defined in lailm 2, wherein said calibration means comprises:

a variable temperature oven encompassing and heating to different ambient temperatures said dielectric resonator and microstrip lines, said ambient temperature being monitored by said temperature sensing means which indicates the ambient temperature around the dielectric resonator and microstrip lines;

a frequency counter which connects with said directional coupler, and, which produces an output signal which indicates the frequency of said clock signal as it passes through the directional coupler; and

a control computer which is electrically connected with said temperature sensing means, and which receives said output signal from said temperature sensing means and said frequency signal from said frequency counter, said control computer producing a correction signal by comparing said frequency with the desired frequency, said control computer sending said temperature reading and said correction signal to printing means after producing it, said control computer sending control signals to said variable temperature oven to direct the heating to different ambient temperature by the variable oven.

4. A temperature sensitive compensation feedback circuit, as defined in claim 3, wherein said dielectric resonator oscillator is deemed a first dielectric rsonator oscillator producing a clock signal #1, and said temperature sensing means comprises:

a temperature sensitive dielectric resonator oscillator which produces a temperature signal which has a frequency drift with changes in ambient temperature;

a second dielectric resonator oscillator producing a clock signal #2;

a first mixer means which produces an output signal by receiving and mixing the temperature signal of the temperature sensitive dielectric resonator oscillator with clock signal #2, said output signal of said first mixer means being the difference between clock signal #2 and said temperature signal; and

a counter means producing the output signal of the temperature sensing means by receiving and counting the output signal of said first mixer means.

5. A temperature compensation feedback circuit, as defined in claim 4 wherein said correlation means comprises a programmable read-only-memory which has been programmed with said correction table which indicates an appropriate amount of phase adjustment required for corresponding ambient temperature readings, said programmable read-only-memory producing said output signals of said correlation means by using said output signal from said temperature sensing means to look up in said correction table an appropriate amount of given adjustment and output the appropriate amount of phase adjustment indicated therein.

6. A temperature compensation feedback circuit, as defined in claim 4 wherein said correlation means comprises a microcomputer which receives a correction algorithm from data obtained using said control computer, said correlation algorithm indicating an appropriate amount of phase adjustment required for corresponding ambient temperature readings to compensate for frequency drift in said clock signals caused by changes in the ambient temperature.

7. A temperature compensation feedback circuit, as defined in claim 3, wherein said temperature sensing means comprises:

a thermistor; and

an A to D converter.

8. A temperature compensation feedback circuit, as defined in claim 7, wherein said correlation means produces control words which are conducted by the digital-to-analog converter to the phase shifter of said dielectric resonator oscillator, said control words causing the phase shifter to correct any frequency drift in the clock signal.

9. A temperature compensation feedback circuit, as defined in claim 8, wherein said correlation means comprises a programmable read-only-memory which has been programmed with said correction table which indicates an appropriate amount of phase adjustment required for corresponding ambient temperature readings, said programmable read-only-memory producing said output signal of said correlation means by using said output signal from said temperature sensing means to look up in said correction table an appropriate amount of phase adjustment and outputting the appropriate amount of phase adjustment indicated therein.

10. A temperature compensation feedback circuit, as defined in claim 8, wherein said correlation means comprises a microcomputer which receives a correction algorithm from data obtained using said control computer, said correlation algorithm indicating an appropriate amount of phase adjustment required for corresponding ambient temperature readings to compensate for frequency drift in said clock signal caused by changes in the ambient temperature.

11. In combination with a dielectric resonator oscillator, including a dielectric resonator which oscillates to produce a radio frequency (RF) clock signal which has phase shift characteristics corresponding to a resonant frequency, said resonant frequency having a frequency drift with changes in ambient temperature, said dielectric resonator oscillator including microstrip lines which are eletrically connected in series with a directional coupler, said microstrip lines being placed in proximity to said dielectric resonator which couples said radio frequency (RF) clock signal between said microstrip lines thus closing the oscillator loop, a temperature compensation feedback process which reduces temperature sensitivity and frequency drift in the clock signal in said microstrip, said process comprising the steps of:

sensing the ambient temperature around the dielectric resonator;

using the ambient temperature to determine a phase shift to be applied to the clock signal which will compensate for frequency drift due to changes in the ambient temperature; and

setting the phase shift in the oscillator loop to compensate for the frequency drift due to changes in ambient temperature.

12. A temperature compensation feedback process, as defined in claim 11, including a calibration step which produces a correction table which indicates an amount of phase adjustment required in said clock signal for corresponding ambient temperature readings, said calibration step comprising the following substeps:

controlling the ambient temperature around the dielectric resonator so that it is set at a plurality of test temperatures;

measuring the frequency in the clock signal as it passes through the directional coupler for each of the test temperatures;

recording an amount of phase shift in the clock signal which compensates for frequency drift at each of the test temperatures;

using the results of the recording step to extrapolate a complete correction table;

sending the correction table to a correlation means which will perform the correlating step of the process.

13. A temperature compensation feedback process, as defined in claim 11, including a calibration step which produces a correction function which indicates an amount of phase adjustment required in said signal for corresponding temperature readings, said calibration step comprising the following substeps:

controlling the ambient temperature around the dielectric resonator so that it is set at a plurality of test temperatures;

measuring the frequency in the clock signal as it passes through the directional coupler for each of the test temperatures;

recording an amount of phase shift in the clock signal which compensates for frequency drift at each of the test temperatures;

using the results of the recording step to generate a correction function; and

sending the correction function to a correlation means which will perform the correlating step of the process.