Matched crystal temperature compensation device

• US 6,522,212 B1
• Filed: 09/18/2000
• Issued: 02/18/2003
• Est. Priority Date: 09/22/1999
• Status: Expired due to Term

• Current Assignee: Optis Wireless Technology, LLC (Brevet Capital)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Kodim, Walter
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US09/664,921
• Time in Patent Office: 883 Days
• Field of Search: 331/176, 331/158, 331/116.R, 331/66, 331/74, 310/311
• US Class Current: 331/176
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03B 5/32 being a piezoelectric resonator selection of piezoelectric material H10N30/00
• CPC Class Codes: H03L 1/025 and a memory for digitally storing correction values
• CPC Class Codes: H03L 1/028 of generators comprising piezoelectric resonators H03L1/021, H03L1/022 take precedence; oscillation generators with a piezoelectric resonator H03B5/32

Abstract

The invention relates to a device and a method for temperature compensation via the determination of cut-angles of a master and a slave crystal (mc, sc) employed in a master and slave oscillator (m, s). When the master and the slave oscillator (m, s) have been tuned to their center frequencies (fc_m, fc_s), then the temperature characteristic of the slave oscillator (s) is actively detuned with respect to the temperature characteristic of the master oscillator (m). In a detuned state a frequency ratio parameter (n_s) of the slave to the master output frequency (f_s/f_m) is determined and the cut-angle is determined by using this parameter (n_s) to read out the cut-angle dependent on the temperature (T) from a memory (MEM). The invention also relates to a temperature compensation device and method where two crystals of different cut-angles are used and a frequency ratio parameter is determined to determine the identity/symmetry or difference of the cut-angles. Particular useful applications of the invention are in dual-mode mobile telephones which require the use of at least two oscillators with different resonant frequencies.

Claims

1. A device for temperature compensation via a determination of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means, tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) at least one second crystal oscillator

including a second crystal which is cut under the same angle as said first crystal and which thus has the same resonant frequency temperature characteristic as said first crystal,

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic, and

including a second tuning means for tuning said second oscillation frequency in response to a second and third control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value; and

said second oscillation frequency temperature characteristic being identical to said first oscillation frequency temperature characteristic when said third control signal is disabled and being detuned thereto when it is enabled;

c) a second crystal oscillator setting means for enabling and setting said third control signal to a control value dependent of a temperature;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

at least one frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency when said first and said second control signals are set to their default values and said third signal is enabled and set to said control value corresponding to said temperature;

a memory means for storing a known relationship of the frequency ratio parameter dependent on the temperature and the cut angle; and

an access means for accessing said memory means with said temperature and said determined frequency ratio parameter and for reading out the cut angle corresponding thereto.

2. A device according to claim 1, wherein

said second tuning means comprises a first and second tuning unit, said first tuning unit (FSTM, D1s) being controlled by said second control signal (s1_ctl) and said second tuning unit being controlled by said third control signal.

3. A device according to claim 1, wherein

said first crystal and said second crystal are taken from a same batch.

4. A device according to claim 1, wherein

said memory means is adapted to store a look-up table containing pre-calculated values representing said frequency ratio parameter of said first to said second oscillation frequency dependent on the cut angle and the temperature in accordance with the detuned second oscillation frequency temperature characteristic;

wherein

said access means is adapted to access said memory means with said determined frequency ratio parameter and said temperature and to read out the cut angle corresponding to the temperature and a stored frequency ratio parameter which has a closest match to said determined frequency ratio parameter.

5. A device according to claim 1, wherein

said frequency ratio determining means comprises

a first counter for counting pulses of the first oscillation frequency of the first crystal oscillator,

at least a second counter for counting pulses of the second oscillation frequency of the second crystal oscillator, and

a maximum comparison means for comparing the first counter count value with a predetermined maximum value,

wherein said processing means further comprises a reset/readout means adapted to read out the second counter count value as said frequency ratio parameter when said maximum comparison means detects that said first counter count value has reached said maximum value and for resetting said first and said second counter,

wherein said access means accesses said memory means with said temperature value and said read out second counter count value.

6. A device according to claim 1, wherein

said memory means is further adapted to store a relationship of the temperature dependent resonant frequency characteristic of the crystals dependent on the temperature and the cut angle,

wherein said processing means further comprises a frequency deviation determining means adapted to read out from said memory means a frequency deviation dependent on said determined cut angle and an ambient temperature value measured by a temperature sensor;

wherein said second crystal oscillator setting means is adapted to disable said third control signal and said first/second control signal setting means is adapted to set said first control signal and said second control signal to a value corresponding to said read out frequency deviation to tune said first and said second crystal oscillator (m, s) back to their center frequencies.

7. A device according to claim 2, wherein

said first tuning unit comprises a voltage tunable capacitor, wherein said first control signal is a voltage signal having a predetermined voltage level.

8. A device according to claim 2, wherein

each of said first and second tuning units comprises a voltage tunable capacitor, wherein said second and third control signals are voltage signals having predetermined voltage levels.

9. A device according to claim 1, wherein

said second tuning means is formed by a single voltage tunable capacitor, wherein said second and third control signals are voltage signals, and by a voltage combiner network combining the second and third control voltage to form a single control voltage for said single voltage tunable capacitor.

10. A device according to claim 1, further comprising

a plurality of second crystal oscillators, a plurality of frequency ratio determining means and an averaging means for averaging said plurality of determined frequency ratio parameters, wherein said access means accesses said memory means with an averaged frequency ratio parameter.

14. A device according to claim 1, wherein

said at least one frequency ratio determining means comprises

a first counter for counting pulses of the first oscillation frequency of the first crystal oscillator,

at least a second counter for counting pulses of the second oscillation frequency of the second crystal oscillator, and

a maximum comparison means for comparing the first counter count value with a predetermined maximum value,

wherein said processing means further comprises a reset/readout means adapted to read out the second counter count value as said frequency ratio parameter when said maximum comparison means detects that said first counter count value has reached said maximum value and for resetting said first and said second counter,

wherein said access means accesses said memory means with said read out second counter count value.

23. A device according to claim 1 employed in a subscriber station of a telecommunication system for operation with a first and at least one second frequency, wherein said first crystal oscillator and said at least one second crystal oscillator provide said first and said at least one second frequencies.

24. A device according to claim 23, wherein

said subscriber station is a multiple standard communication device.

25. A device according to claim 24, wherein

said multiple standard communication device is a dual mode or triple mode mobile telephone, a GSM mobile telephone including GPS or a GSM mobile telephone including DECT.

11. A device for determining the identity of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) a second crystal oscillator

including a second crystal which is cut under an angle and which has a resonant frequency temperature characteristic;

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic; and

including a second tuning means for tuning said second oscillation frequency in response to a second control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value;

c) said second oscillation frequency temperature characteristic being different to said first oscillation frequency temperature characteristic due to a difference in cut-angle of the first and second crystals;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

a frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency at a measurement temperature different to the inflection point temperature of the crystals;

memory means for storing a known relationship of the frequency ratio parameter dependent on the cut-angle of the first crystal and the cut-angle of the second crystal at said measurement temperature;

an access means for accessing said memory means with said determined frequency ratio parameter and for reading out the cut angles of the first and second crystal corresponding thereto; and

a calibration means for determining the identity of the cut-angles on the basis of the read out first and second crystal cut-angles.

12. A device according to claim 11, further comprising

a temperature application means for applying said measurement temperature to each of said first and second oscillators for exposing said oscillators to said measurement temperature (e.g. t=45° C.) and/or a temperature measurement means for determining the current ambient temperature as said measurement temperature.

13. A device according to claim 11, wherein

said memory means is adapted to store a look-up table containing precalculated values representing said frequency ratio parameter of said first to said second oscillation frequency dependent on the cut angles of the first and the second crystal at said measurement temperature at said measurement temperature in accordance with the first and second oscillation frequency temperature characteristic;

wherein

said access means is adapted to access said memory means with said determined frequency ratio parameter determined at said measurement temperature and to read out the first and second cut angle at a stored frequency ratio parameter which has a closest match to said determined frequency ratio parameter at said measurement temperature.

15. A method for temperature compensation via a determination of the cut angle of crystals used in a first and at least one second crystal oscillator having a first tuning means and a second tuning means for tuning the first and second oscillation frequencies in accordance with a first and a second and a third control signal, wherein the first oscillation frequency temperature characteristic and the second oscillation frequency temperature characteristic are identical when said third control signal is disabled and are different if said first control signal is enabled, comprising the following steps:

a) storing in a memory means a known relationship of a frequency ratio parameter dependent on the temperature and the cut-angle;

b) disabling said third control signal and tuning said first and said second oscillation frequencies to their center frequencies by setting the first and the second control signals to default values;

c) enabling said third control signal on and setting said third control signal to a control value dependent of a temperature;

d) measuring the first oscillation frequency and the second oscillation frequency and determining a frequency ratio parameter representing the ratio of the second to the first oscillation frequency;

e) accessing the memory means with said determined frequency ratio parameter and said temperature and reading out the cut angle corresponding thereto.

16. A method according to claim 15, further comprising the steps of

storing in said step a) in said memory means a look-up table containing pre-calculated values representing said frequency ratio parameter of said first to said second oscillation frequency dependent on the cut angle and the temperature in accordance with the detuned second oscillation frequency temperature characteristic; and

accessing in said step e) said memory means with said determined frequency ratio parameter and said temperature and reading out the cut angle corresponding to the temperature value and a stored frequency ratio parameter which has a closest match to said determined frequency ratio parameter.

17. A method according to claim 15, wherein

said step d) comprises the following steps to determine the frequency ratio parameter;

counting pulses of the first oscillation frequency of the first crystal oscillator by a first counter;

counting pulses of the second oscillation frequency of the at least one second crystal oscillator by a second counter, and

comparing by a maximum comparison means the first counter count value with a predetermined maximum value,

reading out the second counter count value as said frequency ratio parameter when said maximum comparison means detects that said first counter count value has reached said maximum value and resetting said first and said second counter, and

accessing said memory means with said temperature and said read out second counter count value.

18. A method according to claim 15, further comprising the steps of

storing in said step a) a relationship of the temperature dependent resonant frequency characteristic of the crystals dependent on temperature and the cut angle, and

after said step e), reading out from said memory means a frequency deviation dependent on said determined cut angle and an ambient temperature value measured by a temperature sensor;

disabling said third control signal and setting said first control signal and said second control signal to a value corresponding to said read out frequency deviation to tune said first and said second crystal oscillator back to their center frequencies.

19. A method for determining the identity of the cut angle of crystals used in a first and a second crystal oscillator having a first tuning means and a second tuning means for tuning the first and second oscillation frequencies in accordance with a first and a second control signal, comprising the following steps:

a) setting said first control signal and said second control signal to default values for tuning the first and second oscillation frequencies to their center frequencies;

b) storing a known relationship of the frequency ratio parameter dependent on the cut-angle of the first crystal and the cut-angle of the second crystal at said measurement temperature in a memory means;

c) measuring the first oscillation frequency and the second oscillation frequency and determining a frequency ratio parameter representing the ratio of the second to the first oscillation frequency at a measurement temperature different to an inflection point temperature of the crystals;

d) accessing said memory means with said determined frequency ratio parameter and reading out the cut angles of the first and second crystal corresponding thereto; and

e) determining the identity of the cut-angles on the basis of the read out first and second crystal cut-angles.

20. A method according to claim 19, wherein

the measurement temperature is the temperature measured ambient temperature or is the temperature set at said oscillators by means of a temperature application means.

21. A method according to claim 19, wherein

said identity of said cut angles is determined by calculating the difference of said determined cut-angles.

22. A method according to claim 19, wherein

said identity of said cut angles is determined by calculating the ratio of said determined cut-angles.

26. A device for temperature compensation via a determination of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) at least one second crystal oscillator

including a second crystal which is cut under the same angle as said first crystal and which thus has the same resonant frequency temperature characteristic as said first crystal,

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic, and

including a second tuning means for tuning said second oscillation frequency in response to a second and third control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value; and

said second oscillation frequency temperature characteristic being identical to said first oscillation frequency temperature characteristic when said third control signal is disabled and being detuned thereto when it is enabled;

c) a second crystal oscillator setting means for enabling and setting said third control signal to a control value dependent of a temperature;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

at least one frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency when said first and said second control signals are set to their default values and said third signal is enabled and set to said control value corresponding to said temperature;

a memory means for storing a known relationship of the frequency ratio parameter dependent on the temperature and the cut angle; and

an access means for accessing said memory means with said temperature and said determined frequency ratio parameter and for reading out the cut angle corresponding thereto; and

e) wherein said memory means is adapted to store a look-up table containing pre-calculated values representing said frequency ratio parameter of said first to said second oscillation frequency dependent on the cut angle and the temperature in accordance with the detuned second oscillation frequency temperature characteristic; and

said access means is adapted to access said memory means with said determined frequency ratio parameter and said temperature and to read out the cut angle corresponding to the temperature and a stored frequency ratio parameter which has a closest match to said determined frequency ratio parameter.

27. A device for temperature compensation via a determination of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) at least one second crystal oscillator

including a second crystal which is cut under the same angle as said first crystal and which thus has the same resonant frequency temperature characteristic as said first crystal,

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic, and

including a second tuning means for tuning said second oscillation frequency in response to a second and third control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value; and

said second oscillation frequency temperature characteristic being identical to said first oscillation frequency temperature characteristic when said third control signal is disabled and being detuned thereto when it is enabled;

c) a second crystal oscillator setting means for enabling and setting said third control signal to a control value dependent of a temperature;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

at least one frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency when said first and said second control signals are set to their default values and said third signal is enabled and set to said control value corresponding to said temperature;

a memory means for storing a known relationship of the frequency ratio parameter dependent on the temperature and the cut angle; and

an access means for accessing said memory means with said temperature and said determined frequency ratio parameter and for reading out the cut angle corresponding thereto; and

e) wherein said frequency ratio determining means comprises

a first counter for counting pulses of the first oscillation frequency of the first crystal oscillator,

at least a second counter for counting pulses of the second oscillation frequency of the second crystal oscillator, and

a maximum comparison means for comparing the first counter count value with a predetermined maximum value,

wherein said processing means further comprises a reset/readout means adapted to read out the second counter count value as said frequency ratio parameter when said maximum comparison means detects that said first counter count value has reached said maximum value and for resetting said first and said second counter,

wherein said access means accesses said memory means with said temperature value and said read out second counter count value.

28. A device for temperature compensation via a determination of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) at least one second crystal oscillator

including a second crystal which is cut under the same angle as said first crystal and which thus has the same resonant frequency temperature characteristic as said first crystal,

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic, and

including a second tuning means for tuning said second oscillation frequency in response to a second and third control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value; and

said second oscillation frequency temperature characteristic being identical to said first oscillation frequency temperature characteristic when said third control signal is disabled and being detuned thereto when it is enabled;

c) a second crystal oscillator setting means for enabling and setting said third control signal to a control value dependent of a temperature;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

at least one frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency when said first and said second control signals are set to their default values and said third signal is enabled and set to said control value corresponding to said temperature;

a memory means for storing a known relationship of the frequency ratio parameter dependent on the temperature and the cut angle; and

an access means for accessing said memory means with said temperature and said determined frequency ratio parameter and for reading out the cut angle corresponding thereto; and

e) wherein said memory means is further adapted to store a relationship of the temperature dependent resonant frequency characteristic of the crystals dependent on the temperature and the cut angle,

wherein said processing means further comprises a frequency deviation determining means adapted to read out from said memory means a frequency deviation dependent on said determined cut angle and an ambient temperature value measured by a temperature sensor;

wherein said second crystal oscillator setting means is adapted to disable said third control signal and said first/second control signal setting means is adapted to set said first control signal and said second control signal to a value corresponding to said read out frequency deviation to tune said first and said second crystal oscillator back to their center frequencies.

29. A device for temperature compensation via a determination of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) at least one second crystal oscillator

including a second crystal which is cut under the same angle as said first crystal and which thus has the same resonant frequency temperature characteristic as said first crystal;

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic, and

including a second tuning means for tuning said second oscillation frequency in response to a second and third control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value; and

said second oscillation frequency temperature characteristic being identical to said first oscillation frequency temperature characteristic when said third control signal is disabled and being detuned thereto when it is enabled;

c) a second crystal oscillator setting means for enabling and setting said third control signal to a control value dependent of a temperature;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

at least one frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency when said first and said second control signals are set to their default values and said third signal is enabled and set to said control value corresponding to said temperature;

a memory means for storing a known relationship of the frequency ratio parameter dependent on the temperature and the cut angle; and

an access means for accessing said memory means with said temperature and said determined frequency ratio parameter and for reading out the cut angle corresponding thereto, and

e) wherein said second tuning means comprises a first and second tuning unit, said first tuning unit being controlled by said second control signal and said second tuning unit being controlled by said third control signal, and

f) wherein said first tuning unit comprises a voltage tunable capacitor, wherein said first control signal is a voltage signal having a predetermined voltage level; and

g) wherein each of said first and second tuning units comprises a voltage tunable capacitor, wherein said second and third control signals are voltage signals having predetermined voltage levels; and

h) wherein said second tuning means is formed by a single voltage tunable capacitor, wherein said second and third control signals are voltage signals, and by a voltage combiner network combining the second and third control voltage to form a single control voltage for said single voltage tunable capacitor.

30. A device for temperature compensation via a determination of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) at least one second crystal oscillator

including a second crystal which is cut under the same angle as said first crystal and which thus has the same resonant frequency temperature characteristic as said first crystal,

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic, and

including a second tuning means for tuning said second oscillation frequency in response to a second and third control signal, said second tuning means tuning said second oscillation frequency a predetermined second center frequency when said second control signal has a second default value; and

said second oscillation frequency temperature characteristic being identical to said first oscillation frequency temperature characteristic when said third control signal is disabled and being detuned thereto when it is enabled;

c) a second crystal oscillator setting means for enabling and setting said third control signal to a control value dependent of a temperature;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

at least one frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency when said first and said second control signals are set to their default values and said third signal is enabled and set to said control value corresponding to said temperature;

a memory means for storing a known relationship of the frequency ratio parameter dependent on the temperature and the cut angle; and

an access means for accessing said memory means with said temperature and said determined frequency ratio parameter and for reading out the cut angle corresponding thereto; and

e) wherein there are provided a plurality of second crystal oscillators, a plurality of frequency ratio determining means and an averaging means for averaging said plurality of determined frequency ratio parameters, wherein said access means accesses said memory means with an averaged frequency ratio parameter.

31. A device for determining the identity of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) a second crystal oscillator

including a second crystal which is cut under an angle and which has a resonant frequency temperature characteristic;

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic; and

including a second tuning means for tuning said second oscillation frequency in response to a second control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value;

c) said second oscillation frequency temperature characteristic being different to said first oscillation frequency temperature characteristic due to a difference in cut-angle of the first and second crystals;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

a frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency at a measurement temperature different to the point temperature of the crystals;

memory means for storing a known relationship of the frequency ratio parameter dependent on the cut-angle of the first crystal and the cut-angle of the second crystal at said measurement temperature;

an access means for accessing said memory means with said determined frequency ratio parameter and for reading out the cut angles of the first and second crystal corresponding thereto; and

a calibration means for determining the identity of the cut-angles on the basis of the read out first and second crystal cut-angles; and

e) a temperature application means for applying said measurement temperature to each of said first and second oscillators for exposing said oscillators to said measurement temperature (e.g. t=45°

C.) and/or a temperature measurement means for determining the current ambient temperature as said measurement temperature.

32. A device for determining the identity of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) a second crystal oscillator

including a second crystal which is cut under an angle and which has a resonant frequency temperature characteristic;

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic; and

including a second tuning means for tuning said second oscillation frequency in response to a second control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value;

c) said second oscillation frequency temperature characteristic being different to said first oscillation frequency temperature characteristic due to a difference in cut-angle of the first and second crystals;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

a frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency at a measurement temperature different to an inflection point temperature of the crystals;

memory means for storing a known relationship of the frequency ratio parameter dependent on the cut-angle of the first crystal and the cut-angle of the second crystal at said measurement temperature;

an access means for accessing said memory means with said determined frequency ratio parameter and for reading out the cut angles of the first and second crystal corresponding thereto; and

a calibration means for determining the identity of the cut-angles on the basis of the read out first and second crystal cut-angles; and

e) wherein said memory means is adapted to store a look-up table containing pre-calculated values representing said frequency ratio parameter of said first to said second oscillation frequency dependent on the cut angles of the first and the second crystal at said measurement temperature at said measurement temperature in accordance with the first and second oscillation frequency temperature characteristic;

wherein

said access means is adapted to access said memory means with said determined frequency ratio parameter determined at said measurement temperature and to read out the first and second cut angle at a stored frequency ratio parameter which has a closest match to said determined frequency ratio parameter at said measurement temperature.

33. A device for determining the identity of the cut angle of crystals used in oscillators, comprising:

a) a first crystal oscillator

including a first crystal, which is cut under an angle and which has a first resonant frequency temperature characteristic,

adapted to output a first oscillation frequency with a first oscillation frequency temperature characteristic determined by said first resonant frequency temperature characteristic, and

including a first tuning means for tuning said first oscillation frequency in response to a first control signal, said first tuning means tuning said first oscillation frequency to a predetermined first center frequency when said first control signal has a first default value;

b) a second crystal oscillator

including a second crystal which is cut under an angle and which has a resonant frequency temperature characteristic;

adapted to output a second oscillation frequency with a second oscillation frequency temperature characteristic, and

including a second tuning means for tuning said second oscillation frequency in response to a second control signal, said second tuning means tuning said second oscillation frequency to a predetermined second center frequency when said second control signal has a second default value;

c) said second oscillation frequency temperature characteristic being different to said first oscillation frequency temperature characteristic due to a difference in cut-angle of the first and second crystals;

d) a processing means

including a first/second control signal setting means for setting said first control signal and said second control signal to their default values;

a frequency ratio determining means for determining a frequency ratio parameter representing the frequency ratio of said second oscillation frequency to said first oscillation frequency at a measurement temperature different to an inflection point temperature of the crystals;

memory means for storing a known relationship of the frequency ratio parameter dependent on the cut-angle of the first crystal and the cut-angle of the second crystal at said measurement temperature;

an access means for accessing said memory means with said determined frequency ratio parameter and for reading out the cut angles of the first and second crystal corresponding thereto; and

a calibration means for determining the identity of the cut-angles on the basis of the read out first and second crystal cut-angles; and

e) said frequency ratio determining means comprises

a first counter for counting pulses of the first oscillation frequency of the first crystal oscillator,

at least a second counter for counting pulses of the second oscillation frequency of the second crystal oscillator, and

a maximum comparison means for comparing the first counter count value with a predetermined maximum value,

wherein said processing means further comprises a reset/readout means adapted to read out the second counter count value as said frequency ratio parameter when said maximum comparison means detects that said first counter count value has reached said maximum value and for resetting said first and said second counter,

wherein said access means accesses said memory means with said read out second counter count value.