WO1996007261A1 - Method of programming a frequency synthesizer and a radio having a frequency synthesizer - Google Patents

Method of programming a frequency synthesizer and a radio having a frequency synthesizer Download PDF

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Publication number
WO1996007261A1
WO1996007261A1 PCT/US1995/010554 US9510554W WO9607261A1 WO 1996007261 A1 WO1996007261 A1 WO 1996007261A1 US 9510554 W US9510554 W US 9510554W WO 9607261 A1 WO9607261 A1 WO 9607261A1
Authority
WO
WIPO (PCT)
Prior art keywords
frequency
synthesizer
tuning
output frequency
loop
Prior art date
Application number
PCT/US1995/010554
Other languages
French (fr)
Inventor
John E. Eberhardt
Ronald L. Bane
Original Assignee
Motorola Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc. filed Critical Motorola Inc.
Priority to CA002198487A priority Critical patent/CA2198487C/en
Priority to AU33678/95A priority patent/AU3367895A/en
Priority to EP95930216A priority patent/EP0777942A4/en
Publication of WO1996007261A1 publication Critical patent/WO1996007261A1/en

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/16—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
    • H03L7/18—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop
    • H03L7/183—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop a time difference being used for locking the loop, the counter counting between fixed numbers or the frequency divider dividing by a fixed number
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J1/00—Details of adjusting, driving, indicating, or mechanical control arrangements for resonant circuits in general
    • H03J1/0008—Details of adjusting, driving, indicating, or mechanical control arrangements for resonant circuits in general using a central processing unit, e.g. a microprocessor
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/16—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
    • H03L7/18—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop
    • H03L7/197—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop a time difference being used for locking the loop, the counter counting between numbers which are variable in time or the frequency divider dividing by a factor variable in time, e.g. for obtaining fractional frequency division

Definitions

  • This invention relates in general to frequency synthesizers in general and particularly to methods of calibrating a frequency synthesizer.
  • the output frequency of a reference oscillator 20 is calibrated or tuned to a predetermined value.
  • a desired output frequency is then produced by adjusting the "N" value of the divide-by-N divider 13 in the synthesizer loop 11.
  • the N value can be mathematically determined simply since the reference oscillator frequency is predetermined.
  • Crystals are subject to variations in tolerance due to manufacturing processes, as well as aging and temperature effects. For example, a reference crystal with a nominal frequency of 10.240 MHz can have a minimum pullability or adjustment of 15 parts per million (PPM) per picofarad (pF).
  • the varactor 26 can be modulated by varying the voltage applied to the varactor 26, thereby providing a varying capacitance and the FM modulation.
  • the local oscillator (LO) frequency for the receiver the pullability is 21.6 KHz. This would make the tolerance of the crystal 20 PPM, which combined with a 10 PPM temperature tolerance and 23 PPM aging tolerance totals 53 PPJ ⁇ , T or 24 KHz at 433.92 MHz.
  • a method of tuning a frequency synthesizer by adjusting the loop divider until the output frequency is close to the desired frequency.
  • the reference oscillator is then adjusted to produce the desired synthesizer output frequency.
  • FIG. 1 is a block diagram of a microprocessor controlled frequency synthesizer that can be utilized in accordance with the present invention.
  • FIG. 1 illustrates a substantially conventional frequency synthesizer 10.
  • the frequency synthesizer 10 includes a synthesizer loop 11, having a conventional voltage control oscillator 12, divide-by-N loop divider 13, phase comparator 14, and integrator/filter 15, which serves as a loop filter.
  • the N value of the loop divider 13 is provided, as by a controller such as microprocessor 16.
  • the reference signal is provided to comparator 14 as by reference oscillator 20 and amplifier 21. If desired, the amplifier 21 can be included on a single integrated circuit with components of the synthesizer loop 11.
  • Reference oscillator 20 includes a crystal 22, a load circuit composed of capacitors 23, 24, 25, and a varactor or variable capacitor 26.
  • a coupling or DC blocking capacitor 27 couples varactor 26 to crystal 22, while resistors 28 and 29 are used for DC biasing purposes.
  • a DC voltage is derived from an output of microprocessor 16 by a digital-to-analog converter (D/A) 30, which can be a simple, discrete D/A implementation in th preferred implementation.
  • the DC voltage from D/A 30 is applied to the varactor 26 to change the capacitance of the varactor 26 and thereby pull or warp the output frequency of crystal 22.
  • D/A digital-to-analog converter
  • Tuning values can be stored in a memory such as an EEPROM (not shown) associated with microprocessor 16. Since the crystal 22 is not necessarily a high precision crystal, the varactor 26 may not be capable of pulling the crystal 22 to a desired nominal oscillator frequency.
  • the synthesizer loop 11 is coarse tuned by adjusting the divisor "N" of the loop divider 13 until the output frequency is close to the desired output frequency.
  • the reference oscillator 20 is then adjusted by tuning the value applied to D/A 30 and consequently, the analog voltage applied to varactor 26, until a desired VCO output frequency has been obtained.
  • the coarse and fine tuning values for this particular output frequency can then be stored.
  • Additional VCO output frequencies can be determined and stored in a similar manner, as, for example, a transmit or receive frequency that is offset from the other frequency, or another channel for a radio.
  • the varactor 26 is tuned towards one limit of its tuning range by D/A 30 prior to tuning the divider 13.
  • Divider 13 is then tuned (by selecting values of "N") until it is within tuning range of the varactor 26.
  • the input to D/A 30 is then changed to tune the varactor 26 to warp the crystal 22 in order to provide the desired VCO frequency.
  • any desired VCO output frequency is provided by iteratively tuning first the N value applied divide-by-N divider 13 and then by iteratively adjusting the digital value applied to D/A 30 until the desired VCO output frequency has substantially been achieved.

Abstract

In order to program the output frequency of a synthesizer such as that of a two-way radio, first the reference oscillator (20) is warped or tuned substantially to one limit of its tuning range. The 'N' divisor of the synthesizer divider (13) is then selected to produce a loop output close to the desired loop output frequency. The reference oscillator (20) is then tuned to provide the desired loop output frequency.

Description

METHOD OF PROGRAMMING A FREQUENCY SYNTHESIZER AND A RADIO HAVING A FREQUENCY SYNTHESIZER
Technical Field This invention relates in general to frequency synthesizers in general and particularly to methods of calibrating a frequency synthesizer.
Background In a typical frequency synthesizer, such as the circuit illustrated in FIG. 1, the output frequency of a reference oscillator 20 is calibrated or tuned to a predetermined value. A desired output frequency is then produced by adjusting the "N" value of the divide-by-N divider 13 in the synthesizer loop 11. The N value can be mathematically determined simply since the reference oscillator frequency is predetermined. When utilizing this approach, it is necessary that the crystal oscillator 20 be capable of being tuned to this predetermined value. Crystals are subject to variations in tolerance due to manufacturing processes, as well as aging and temperature effects. For example, a reference crystal with a nominal frequency of 10.240 MHz can have a minimum pullability or adjustment of 15 parts per million (PPM) per picofarad (pF). This translates to a maximum of 22 KHz at a transmit frequency of 433.92 MHz when a tuning varactor is moved 3.4 PF. If the synthesizer is used in a transmitter that is frequency modulated, the varactor 26 can be modulated by varying the voltage applied to the varactor 26, thereby providing a varying capacitance and the FM modulation. At 423.225 MHz, the local oscillator (LO) frequency for the receiver, the pullability is 21.6 KHz. This would make the tolerance of the crystal 20 PPM, which combined with a 10 PPM temperature tolerance and 23 PPM aging tolerance totals 53 PPJ\,T or 24 KHz at 433.92 MHz. In this application, a tighter crystal specification would be needed (at a higher cost), if the reference oscillator were tuned by the varactor only. A tuning approach that permits the use of a less precise and less expensive crystal while permitting tuning operation of the frequency synthesizer to produce a desired output would be desirable. Summary of the Invention
Briefly, according to the invention, there is provided a method of tuning a frequency synthesizer by adjusting the loop divider until the output frequency is close to the desired frequency. The reference oscillator is then adjusted to produce the desired synthesizer output frequency.
Brief Description of the Drawings
FIG. 1 is a block diagram of a microprocessor controlled frequency synthesizer that can be utilized in accordance with the present invention.
Detailed Description of the Preferred Embodiment
The method of programming a frequency synthesizer or a radio having a synthesizer can be best understood by review of FIG. 1, which illustrates a substantially conventional frequency synthesizer 10. The frequency synthesizer 10 includes a synthesizer loop 11, having a conventional voltage control oscillator 12, divide-by-N loop divider 13, phase comparator 14, and integrator/filter 15, which serves as a loop filter. The N value of the loop divider 13 is provided, as by a controller such as microprocessor 16. The reference signal is provided to comparator 14 as by reference oscillator 20 and amplifier 21. If desired, the amplifier 21 can be included on a single integrated circuit with components of the synthesizer loop 11.
Reference oscillator 20 includes a crystal 22, a load circuit composed of capacitors 23, 24, 25, and a varactor or variable capacitor 26. A coupling or DC blocking capacitor 27 couples varactor 26 to crystal 22, while resistors 28 and 29 are used for DC biasing purposes. A DC voltage is derived from an output of microprocessor 16 by a digital-to-analog converter (D/A) 30, which can be a simple, discrete D/A implementation in th preferred implementation. The DC voltage from D/A 30 is applied to the varactor 26 to change the capacitance of the varactor 26 and thereby pull or warp the output frequency of crystal 22. It should be understood that the specific illustrated reference oscillator topology and loop topology are not critical and other circuit topologies can be utilized with this method. Tuning values can be stored in a memory such as an EEPROM (not shown) associated with microprocessor 16. Since the crystal 22 is not necessarily a high precision crystal, the varactor 26 may not be capable of pulling the crystal 22 to a desired nominal oscillator frequency.
To program a desired VCO output frequency for applications such as a radio transmitter or receiver, the synthesizer loop 11 is coarse tuned by adjusting the divisor "N" of the loop divider 13 until the output frequency is close to the desired output frequency. The reference oscillator 20 is then adjusted by tuning the value applied to D/A 30 and consequently, the analog voltage applied to varactor 26, until a desired VCO output frequency has been obtained. The coarse and fine tuning values for this particular output frequency can then be stored.
Additional VCO output frequencies can be determined and stored in a similar manner, as, for example, a transmit or receive frequency that is offset from the other frequency, or another channel for a radio. Preferably, the varactor 26 is tuned towards one limit of its tuning range by D/A 30 prior to tuning the divider 13. Divider 13 is then tuned (by selecting values of "N") until it is within tuning range of the varactor 26. The input to D/A 30 is then changed to tune the varactor 26 to warp the crystal 22 in order to provide the desired VCO frequency. Essentially, any desired VCO output frequency is provided by iteratively tuning first the N value applied divide-by-N divider 13 and then by iteratively adjusting the digital value applied to D/A 30 until the desired VCO output frequency has substantially been achieved.
While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

Claims
1. A method of tuning a frequency synthesizer to a desired frequency, comprising the steps of: coarse tuning the frequency synthesizer by adjusting the divisor of the loop divider until the output frequency is close to the desired frequency; and then adjusting the reference oscillator to produce the desired output frequency.
2. A method of programming the output frequency of a synthesized radio comprising the steps of: coarse tuning the synthesized radio by changing the divisor of the loop divider; fine tuning the synthesized radio by warping the loop reference oscillator; and storing the coarse and fine tuning values.
3. A method of programming the operating frequency of a synthesized radio as defined in claim 2, comprising the further steps of: repeating the steps of claim 2 to coarse and fine tune the synthesized radio for at least a second frequency; and and storing the coarse and fine tuning for the second frequency.
4. A method of programming a synthesizer, comprising the steps of: operating a controller to provide "N" values to a divide-by-N divider; selecting a value of "N" that approximately provides a desired output frequency; operating the controller to provide digital values corresponding to analog voltage values; applying the analog voltage values to a tunable loop reference oscillator to pull the oscillator frequency; and selecting a digital value that corresponds to desired loop output frequency.
PCT/US1995/010554 1994-08-30 1995-08-18 Method of programming a frequency synthesizer and a radio having a frequency synthesizer WO1996007261A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
CA002198487A CA2198487C (en) 1994-08-30 1995-08-18 Method of programming a frequency synthesizer and a radio having a frequency synthesizer
AU33678/95A AU3367895A (en) 1994-08-30 1995-08-18 Method of programming a frequency synthesizer and a radio having a frequency synthesizer
EP95930216A EP0777942A4 (en) 1994-08-30 1995-08-18 Method of programming a frequency synthesizer and a radio having a frequency synthesizer

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US08/298,492 1994-08-30
US08/298,492 US5570066A (en) 1994-08-30 1994-08-30 Method of programming a frequency synthesizer

Publications (1)

Publication Number Publication Date
WO1996007261A1 true WO1996007261A1 (en) 1996-03-07

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Family Applications (1)

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PCT/US1995/010554 WO1996007261A1 (en) 1994-08-30 1995-08-18 Method of programming a frequency synthesizer and a radio having a frequency synthesizer

Country Status (5)

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US (1) US5570066A (en)
EP (1) EP0777942A4 (en)
AU (1) AU3367895A (en)
CA (1) CA2198487C (en)
WO (1) WO1996007261A1 (en)

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EP0905878A2 (en) * 1997-09-30 1999-03-31 Siemens Aktiengesellschaft Modulator for generating a RF signal

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US6249155B1 (en) 1997-01-21 2001-06-19 The Connor Winfield Corporation Frequency correction circuit for a periodic source such as a crystal oscillator
US5881374A (en) * 1997-01-31 1999-03-09 Telefonaktiebolaget L M Ericsson (Publ) Circuitry and method for detecting frequency deviation caused by aging of an oscillator
US5952890A (en) * 1997-02-05 1999-09-14 Fox Enterprises, Inc. Crystal oscillator programmable with frequency-defining parameters
US5960405A (en) * 1997-02-05 1999-09-28 Fox Enterprises, Inc. Worldwide marketing logistics network including strategically located centers for frequency programming crystal oscillators to customer specification
CN1153352C (en) 1997-03-18 2004-06-09 皇家菲利浦电子有限公司 Receiver tuning system
WO1998042076A2 (en) * 1997-03-18 1998-09-24 Koninklijke Philips Electronics N.V. Receiver tuning system
EP0905910A3 (en) * 1997-09-25 2003-04-16 Siemens Aktiengesellschaft Process and apparatus for changing frequency in a multichannel radio system
FR2790790B1 (en) 1999-03-12 2001-04-27 Siemens Automotive Sa METHOD FOR DETERMINING THE PRESSURE IN THE FUEL INJECTION RAMP OF AN INTERNAL COMBUSTION ENGINE AND CORRESPONDING DEVICE
US6323739B1 (en) 2000-01-18 2001-11-27 Denso Corporation Adjusting untrimmed VCO during operation of the oscillator
DE60115158T2 (en) 2000-06-28 2006-06-29 Thomson Licensing High-frequency oscillator
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Also Published As

Publication number Publication date
CA2198487A1 (en) 1996-03-07
EP0777942A4 (en) 1997-12-17
CA2198487C (en) 1999-11-09
EP0777942A1 (en) 1997-06-11
US5570066A (en) 1996-10-29
AU3367895A (en) 1996-03-22

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