Crystal oscillator with automatic compensation for aging and temperature

• US 5,875,388 A
• Filed: 07/18/1997
• Issued: 02/23/1999
• 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): Chin, Wellington
• Assistant Examiner(s): SOBUTKA, PHILIP
• Application Number:
  US08/896,697
• Time in Patent Office: 585 Days
• Field of Search: 455/550, 455/575, 455/84, 455/75-77, 455/67.1, 455/226.1, 455/115, 455/255.7, 455/259, 455/265, 331/158, 331/176
• US Class Current: 455/67.11
• 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 radiotelephone with compensation for temperature and aging of a crystal oscillator circuit using a reference frequency, comprising:

a converter responsive to a received radio frequency (RF) signal and a local reference signal for providing an intermediate frequency (IF) signal;

a limiter/demodulator connected to said converter and responsive to said IF signal for providing a limited IF signal and an audio signal;

an audio circuit connected to said limiter/demodulator for providing an amplified audio output signal;

a crystal oscillator circuit responsive to a frequency correction value for providing said local reference signal at a tunable frequency of operation;

a temperature sensing device for providing a temperature reading;

a controller having a plurality of frequency-temperature correction values and an aging correction value, for reading said temperature reading from said temperature sensing device, for selecting a said frequency-temperature correction value based upon said temperature reading, for combining said aging correction value and said selected frequency-temperature correction value to provide said frequency correction value, for applying said frequency correction value to said crystal oscillator circuit, for determining a frequency relationship between said local reference signal and said limited IF signal, for changing said frequency correction value by a first predetermined amount and providing said frequency correction value to said crystal oscillator circuit if said frequency relationship is greater than a first predetermined value, for determining whether said frequency relationship is greater than a second predetermined value if said frequency relationship 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 crystal oscillator circuit if said frequency relationship is greater than said second predetermined value, and for updating said aging correction value to compensate for said frequency relationship if said frequency relationship is less than said second predetermined value by determining an updated aging correction value from said frequency correction value and said frequency-temperature correction value and storing said updated aging correction value as said aging correction value; and

a transmitter section responsive to said local reference signal and an audio input signal for providing a transmitted RF signal.

2. The radiotelephone of claim 1 wherein said converter comprises:

a first local oscillator for providing a first local oscillator signal;

a phase locked loop responsive to said first local oscillator signal and said local reference signal for controlling the frequency of said first local oscillator signal;

a first mixer for combining said received RF signal and said local oscillator signal to provide a first IF signal;

a second local oscillator responsive to said local reference signal for providing a second local oscillator signal; and

a second mixer for combining said first IF signal and said second local oscillator signal to provide said IF signal to said limiter/demodulator.

3. The radiotelephone of claim 1 wherein said controller comprises:

a memory for storing a table having said plurality of frequency-temperature correction values, and for storing said aging correction value, each said frequency-temperature correction value being for a predetermined temperature; and

a microprocessor responsive to said frequency relationship for reading said temperature, for selecting said frequency-temperature correction value, for determining said frequency correction value, for determining said frequency relationship, for changing said frequency correction value, for determining said updated aging correction value, and for storing said updated aging correction value in said table in said memory.

4. The radiotelephone of claim 1 wherein said controller comprises a counter for determining said frequency relationship between said local reference signal and said limited IF signal.

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

a converter responsive to a received radio frequency (RF) signal and a local reference signal for providing an intermediate frequency (IF) signal;

a limiter/demodulator connected to said converter and responsive to said IF signal for providing a limited IF signal and an audio signal;

an audio circuit connected to said limiter/demodulator for providing an amplified audio output signal;

a crystal oscillator circuit responsive to a frequency correction value for providing said local reference signal at a tunable frequency of operation;

a temperature sensing device for providing a temperature reading; and

a controller having a plurality of frequency-temperature correction values and an aging correction value, for reading said temperature reading from said temperature sensing device, for selecting a said frequency-temperature correction value based upon said temperature reading, for combining said aging correction value and said selected frequency-temperature correction value to provide said frequency correction value, for applying said frequency correction value to said crystal oscillator circuit, for determining a frequency relationship between said local reference signal and said limited IF signal, for changing said frequency correction value by a first predetermined amount and providing said frequency correction value to said crystal oscillator circuit if said frequency relationship is greater than a first predetermined value, for determining whether said frequency relationship is greater than a second predetermined value if said frequency relationship 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 crystal oscillator circuit if said frequency relationship is greater than said second predetermined value, and for updating said aging correction value to compensate for said frequency relationship if said frequency relationship is less than said second predetermined value by determining an updated aging correction value from said frequency correction value and said frequency-temperature correction value and storing said updated aging correction value as said aging correction value.

6. The radiotelephone of claim 5 wherein said converter comprises:

a first local oscillator for providing a first local oscillator signal;

a phase locked loop responsive to said first local oscillator signal and said local reference signal for controlling the frequency of said first local oscillator signal;

a first mixer for combining said received RF signal and said local oscillator signal to provide a first IF signal;

a second local oscillator responsive to said local reference signal for providing a second local oscillator signal; and

a second mixer for combining said first IF signal and said second local oscillator signal to provide said IF signal to said limiter/demodulator.

7. The radiotelephone of claim 5 wherein said controller comprises:

a memory for storing a table having said plurality of frequency-temperature correction values, and for storing said aging correction value, each said frequency-temperature correction value being for a predetermined temperature; and

a microprocessor responsive to said frequency relationship for reading said temperature, for selecting said frequency-temperature correction value, for determining said frequency correction value, for determining said frequency relationship, for changing said frequency correction value, for determining said updated aging correction value, and for storing said updated aging correction value in said table in said memory.

8. The radiotelephone of claim 5 wherein said controller comprises a counter for determining said frequency relationship between said local reference signal and said limited IF signal.

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

a converter responsive to a received radio frequency (RF) signal and a local reference signal for providing an intermediate frequency (IF) signal;

a limiter/demodulator connected to said converter and responsive to said IF signal for providing a limited IF signal and an audio signal;

an audio circuit connected to said limiter/demodulator for providing an amplified audio output signal;

a crystal oscillator circuit responsive to a frequency correction value for providing, said local reference signal at a tunable frequency of operation;

a temperature sensing device for providing a temperature reading;

a controller having a plurality of combined frequency-temperature and aging correction values, for reading said temperature reading from said temperature sensing device, for selecting a said combined frequency-temperature and aging correction value based upon said temperature reading to provide a frequency correction value, for applying said frequency correction value to said crystal oscillator circuit, for determining a frequency relationship between said local reference signal and said limited IF signal, for changing said frequency correction value by a first predetermined amount and providing said frequency correction value to said crystal oscillator circuit if said frequency relationship is greater than a first predetermined value, for determining whether said frequency relationship is greater than a second predetermined value if said frequency relationship 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 crystal oscillator circuit if said frequency relationship is greater than said second predetermined value, and for updating, said selected combined frequency-temperature and aging correction value to compensate for said frequency relationship if said frequency relationship is less than said second predetermined value by determining an updated combined frequency-temperature and aging correction value from said frequency correction value and storing said updated combined frequency-temperature and aging correction value as said selected combined frequency-temperature and aging correction value; and

a transmitter section responsive to said local reference signal and an audio input signal for providing a transmitted RF signal.

10. The radiotelephone of claim 9 wherein said converter comprises:

a first local oscillator for providing a first local oscillator signal;

a phase locked loop responsive to said first local oscillator signal and said local reference signal for controlling the frequency of said first local oscillator signal;

a first mixer for combining said received RF signal and said local oscillator signal to provide a first IF signal;

a second local oscillator responsive to said local reference signal for providing a second local oscillator signal; and

a second mixer for combining said first IF signal and said second local oscillator signal to provide said IF signal to said limiter/demodulator.

11. The radiotelephone of claim 9 wherein said controller comprises:

a memory for storing a table having said plurality of said combined frequency-temperature and aging correction values, and for storing said combined frequency-temperature and aging correction value, each said combined frequency-temperature and aging correction value being for a predetermined temperature; and

a microprocessor responsive to said frequency relationship for reading said temperature, for selecting said combined frequency-temperature and aging correction value, for determining said frequency correction value, for determining said frequency relationship, for changing said frequency correction value, for determining said updated combined frequency-temperature and aging correction value, and for storing said updated combined frequency-temperature and aging correction value in said table in said memory.

12. The radiotelephone of claim 9 wherein said controller comprises a counter for determining said frequency relationship between said local reference signal and said limited IF signal.

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

a converter responsive to a received radio frequency (RF) signal and a local reference signal for providing an intermediate frequency (IF) signal;

a limiter/demodulator connected to said converter and responsive to said IF signal for providing a limited IF signal and an audio signal;

an audio circuit connected to said limiter/demodulator for providing an amplified audio output signal;

a crystal oscillator circuit responsive to a frequency correction value for providing said local reference signal at a tunable frequency of operation;

a temperature sensing device for providing a temperature reading; and

a controller having a plurality of combined frequency-temperature and aging correction values, for reading said temperature reading from said temperature sensing device, for selecting a said combined frequency-temperature and aging correction value based upon said temperature reading to provide a frequency correction value, for applying said frequency correction value to said crystal oscillator circuit, for determining a frequency relationship between said local reference signal and said limited IF signal, for changing said frequency correction value by a first predetermined amount and providing said frequency correction value to said crystal oscillator circuit if said frequency relationship is greater than a first predetermined value, for determining whether said frequency relationship is greater than a second predetermined value if said frequency relationship 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 crystal oscillator circuit if said frequency relationship is greater than said second predetermined value, and for updating said selected combined frequency-temperature and aging correction value to compensate for said frequency relationship if said frequency relationship is less than said second predetermined value by determining an updated combined frequency-temperature and aging correction value from said frequency correction value and storing said updated combined frequency-temperature and aging correction value as said selected combined frequency-temperature and aging correction value.

14. The radiotelephone of claim 13 wherein said converter comprises:

a first local oscillator for providing a first local oscillator signal;

a phase locked loop responsive to said first local oscillator signal and said local reference signal for controlling the frequency of said first local oscillator signal;

a first mixer for combining said received RF signal and said local oscillator signal to provide a first IF signal;

a second local oscillator responsive to said local reference signal for providing a second local oscillator signal; and

a second mixer for combining said first IF signal and said second local oscillator signal to provide said IF signal to said limiter/demodulator.

15. The radiotelephone of claim 13 wherein said controller comprises:

a memory for storing a table having said plurality of frequency-temperature correction values, and for storing said aging correction value, each said frequency-temperature correction value being for a predetermined temperature; and

a microprocessor responsive to said frequency relationship for reading said temperature, for selecting said frequency-temperature correction value, for determining said frequency correction value, for determining said frequency relationship, for changing said frequency correction value, for determining said updated aging correction value, and for storing said updated aging correction value in said table in said memory.

16. The radiotelephone of claim 13 wherein said controller comprises a counter for determining said frequency relationship between said local reference signal and said limited IF signal.