System with automatic compensation for aging and temperature of a crystal oscillator

• US 5,659,884 A
• Filed: 02/10/1995
• Issued: 08/19/1997
• Est. Priority Date: 02/10/1995
• Status: Expired due to Fees

• Current Assignee: Matsushita Communication Industrial Corporation of USA (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Communication Industrial Corporation of USA (Panasonic Holdings Corporation)
• Inventors: Daughtry, Earl A. Jr., Quire, Christopher S., Ruff, Mark A., Stone, Richard M.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): SOBUTKA, PHILIP
• Application Number:
  US08/387,058
• Time in Patent Office: 921 Days
• Field of Search: 455/84, 455/75, 455/76, 455/77, 455/67.1, 455/115, 455/120, 455/123, 455/226.1, 455/257, 455/259, 455/265, 331/176, 331/158
• US Class Current: 455/75
• CPC Class Codes: H03B 5/32 being a piezoelectric resonator selection of piezoelectric material H10N30/00
• CPC Class Codes: H03J 1/0033 for voltage synthesis with a D/A converter
• CPC Class Codes: H03J 7/06 using counters or frequency dividers
• CPC Class Codes: H03L 1/00 Stabilisation of generator output against variations of physical values, e.g. power supply
• CPC Class Codes: H03L 1/025 and a memory for digitally storing correction values
• CPC Class Codes: H04B 1/26 for superheterodyne receivers multiple frequency-changing H03D7/16
• CPC Class Codes: H04W 4/18 Information format or content conversion, e.g. adaptation by the network of the transmitted or received information for the purpose of wireless delivery to users or terminals
• CPC Class Codes: H04W 88/02 Terminal devices

Abstract

A method and an apparatus for compensating for aging and temperature of the crystal in a crystal oscillator. An RF signal which is transmitted by a mobile telephone switching office (MTSO) (108) and received by the antenna (118). The signal transmitted by the MTSO (108) serves as an external reference. A crystal-controlled main oscillator/time base generator (134) provides a local reference frequency to the converters (120) and provides a time base signal to a counter (136). A controller (112) reads an aging correction value from a memory and provides a frequency control signal to the main oscillator (134). The converters (120) convert the received RF signal to an IF frequency. A limiter (122) provides a limited IF signal to the counter (136). Counter (136) counts the number of cycles of the limited IF signal that appear in a cycle of the time base signal. A controller (112) compares this measured count to a reference count and the count error is determined. The count error is compared to an allowable count error. If the count error is excessive then the controller (112) adjusts the frequency control signal provided to the main oscillator (134) so as to change the frequency of the main oscillator (134). Once the controller (112) has shifted the frequency so that the count error is not excessive then the controller (112) stores the new aging correction value. The measured count is therefore depends upon the frequency of the main oscillator (134) and the frequency of the received signal. This process automatically compensates for the frequency of the main oscillator (134) and, therefore, for aging of the crystal. The frequency of oscillation of the main oscillator (134) is therefore as accurate as the external reference, typically the highly accurate MTSO (108). A high precision oscillator (134) has thus been obtained using an external reference (MTSO 108) and an aging correction value.

Claims

1. A radio frequency circuit with compensation for temperature and aging of a crystal oscillator using a reference frequency, comprising:

a crystal;

a tuning device responsive to a frequency correction value for tuning the frequency of oscillation of said crystal to a desired frequency of operation;

an oscillator circuit connected to said crystal and said tuning device for causing said crystal to oscillate at said radio frequency;

a temperature sensing device for providing a temperature reading;

a memory containing a plurality of frequency-temperature correction values and an aging correction value; and

a controller for reading said temperature reading from said temperature sensing device, for reading said aging correction value from said memory, for reading a said frequency-temperature correction value from said memory for said temperature reading, for combining said aging correction value and said frequency-temperature correction value to provide said frequency correction value, for applying said frequency correction value to said tuning device, for determining a frequency difference between the frequency of said oscillator and said reference frequency, for changing said frequency correction value by a first predetermined amount and providing said frequency correction value to said oscillator if said frequency difference is greater than a first predetermined value, for determining whether said frequency difference is greater than a second predetermined value if said frequency difference is less than said first predetermined value, for changing said frequency correction value by a second predetermined amount and providing said frequency correction value to said oscillator if said frequency difference is greater than said second predetermined value, and for updating said aging correction value in said memory to compensate for said frequency difference if said frequency difference is less than said second predetermined value by determining an updated aging correction value from said frequency correction value and storing said updated aging correction value as said aging correction value.

2. A radio frequency circuit with compensation for temperature and aging of a crystal oscillator using a reference frequency, comprising:

a crystal;

a tuning device responsive to a frequency correction value for tuning the frequency of oscillation of said crystal to a desired frequency of operation;

an oscillator circuit connected to said crystal and said tuning device for causing said crystal to oscillate at said radio frequency;

a temperature sensing device for providing a temperature reading;

a memory containing a plurality of combined temperature and aging correction values; and

a controller for reading said temperature reading from said temperature sensing device, for reading a said combined temperature and aging correction value from said memory for said temperature reading, for applying said combined temperature and aging correction value as said frequency correction value to said tuning device, for determining a frequency difference between the frequency of said oscillator and said reference frequency, for changing said frequency correction value by a first predetermined amount and providing said frequency correction value to said oscillator if said frequency difference is greater than a first predetermined value, for determining whether said frequency difference is greater than a second predetermined value if said frequency difference is less than said first predetermined value, for changing said frequency correction value by a second predetermined amount and providing said frequency correction value to said oscillator if said frequency difference is greater than said second predetermined value, and for updating said combined temperature and aging correction value in said memory to compensate for said frequency difference if said frequency difference is less than said second predetermined value by storing said frequency correction value as said combined temperature and aging correction value.

3. A method for compensating for aging of a crystal in an oscillator using a reference frequency, comprising the steps of:

(a) determining a temperature of operation for said oscillator;

(b) obtaining a combined aging and temperature correction value for said oscillator at said temperature;

(c) providing said combined aging and temperature correction value as a frequency correction value to said oscillator;

(d) determining a frequency difference between the frequency of said oscillator and said reference frequency;

(e) if said frequency difference is greater than a first predetermined value then changing said combined aging and temperature correction value by a first predetermined amount, providing said combined aging and temperature correction value to said oscillator, and then returning to step (d);

(f) if said frequency difference is less than said first predetermined value then determining whether said frequency difference is greater than a second predetermined value;

(g) if said frequency difference is greater than said second predetermined value then changing said frequency correction value by a second predetermined amount, providing said frequency correction value to said oscillator, determining said frequency difference, and then repeating this step (g);

(h) if said frequency difference is less than said second predetermined value then updating said combined aging and temperature correction value to compensate for said frequency difference by storing said frequency correction value as said combined temperature and aging correction value.

4. The method of claim 3 wherein said step of updating said combined aging and temperature correction value further comprises:

if said frequency difference is not less than a maximum frequency difference then adjusting said frequency correction value, providing said frequency correction value to said oscillator, and determining said frequency difference between said frequency of said oscillator and said reference frequency, and repeating said steps of adjusting said frequency correction value, providing said frequency correction value, and determining said frequency difference until said frequency difference is less than said maximum frequency difference; and

storing said updated combined aging and temperature correction value as said combined aging and temperature correction value only if said frequency difference is less than said maximum frequency difference.

5. The method of claim 4 wherein said step of determining said updated combined aging and temperature correction value further comprises:

using said frequency correction value as said updated combined aging and temperature correction value.

6. The method of claim 4 wherein said step of determining said updated combined aging and temperature correction value further comprises:

determining a correction difference between said frequency correction value and said combined aging and temperature correction value; and

if said correction difference is less than a maximum correction difference then using said frequency correction value as said updated combined aging and temperature correction value.

7. The method of claim 4 wherein said step of determining said updated combined aging and temperature correction value further comprises:

determining a correction difference between said frequency correction value and said combined aging and temperature correction value; and

if said correction difference is greater than a minimum correction difference and less than a maximum correction difference then using said frequency correction value as said updated combined aging and temperature correction value.

8. A method for compensating for aging of a crystal in an oscillator using a reference frequency, comprising the steps of:

(a) determining a temperature of operation for said oscillator;

obtaining a frequency-temperature correction value for said oscillator for said temperature;

(c) obtaining an aging correction value for said oscillator;

(d) combining said frequency-temperature correction value and said aging correction value to provide an initial frequency correction value;

(e) providing said initial frequency correction value as a frequency correction value to said oscillator;

(f) determining a frequency difference between the frequency of said oscillator and said reference frequency;

(g) if said frequency difference is greater than a first predetermined value then changing said frequency correction value by a first predetermined amount, providing said frequency correction value to said oscillator, and then returning to step (f);

(h) if said frequency difference is less than said first predetermined value then determining whether said frequency difference is greater than a second predetermined value;

(i) if said frequency difference is greater than said second predetermined value then changing said frequency correction value by a second predetermined amount, providing said frequency correction value to said oscillator, determining said frequency difference, and then repeating this step (i);

(j) if said frequency difference is less than said second predetermined value then updating said aging correction value to compensate for said frequency difference by determining an updated aging correction value from said frequency correction value and storing said updated aging correction value as said aging correction value.

9. The method of claim 8 wherein said step of updating said aging correction value further comprises:

storing said updated aging correction value as said aging correction value only if said frequency difference is also less than a maximum frequency difference.

10. The method of claim 8 wherein said step of updating said aging correction value further comprises:

if said frequency difference is not less than a maximum frequency difference then adjusting said frequency correction value, providing said frequency correction value to said oscillator, and determining said frequency difference between said frequency of said oscillator and said reference frequency, and repeating said steps of adjusting said frequency correction value, providing said frequency correction value, and determining said frequency difference until said frequency difference is less than said maximum frequency difference; and

storing said updated aging correction value as said aging correction value only if said frequency difference is also less than said maximum frequency difference.

11. The method of claims 9 or 10 wherein said step of determining said updated aging correction value further comprises:

determining a correction difference between said frequency correction value and said frequency-temperature correction value; and

using said correction difference as said updated aging correction value.

12. The method of claims 9 or 10 wherein said step of determining said updated aging correction value further comprises:

determining a correction difference between said frequency correction value and said frequency-temperature correction value; and

if said correction difference is less than a maximum correction difference then using said correction difference as said updated aging correction value.

13. The method of claims 9 or 10 wherein said step of determining said new updated aging correction value further comprises:

determining a correction difference between said frequency correction value and said frequency-temperature correction value; and

if said correction difference is greater than a minimum correction difference and less than a maximum correction difference then using said correction difference as said updated aging correction value.