System with automatic compensation for aging and temperature of a crystal oscillator
First Claim
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.
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Accused Products
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.
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Citations
13 Claims
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1. A radio frequency circuit with compensation for temperature and aging of a crystal oscillator using a reference frequency, comprising:
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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.
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2. A radio frequency circuit with compensation for temperature and aging of a crystal oscillator using a reference frequency, comprising:
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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.
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3. A method for compensating for aging of a crystal in an oscillator using a reference frequency, comprising the steps of:
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(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. - View Dependent Claims (4, 5, 6, 7)
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8. A method for compensating for aging of a crystal in an oscillator using a reference frequency, comprising the steps of:
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(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. - View Dependent Claims (9, 10, 11, 12, 13)
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Specification