WO2009023019A1 - Circuit de réglage de fréquence d'oscillateur cristallin - Google Patents

Circuit de réglage de fréquence d'oscillateur cristallin Download PDF

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Publication number
WO2009023019A1
WO2009023019A1 PCT/US2007/075691 US2007075691W WO2009023019A1 WO 2009023019 A1 WO2009023019 A1 WO 2009023019A1 US 2007075691 W US2007075691 W US 2007075691W WO 2009023019 A1 WO2009023019 A1 WO 2009023019A1
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WO
WIPO (PCT)
Prior art keywords
capacitor
frequency tuning
tuning circuit
switched
switchable
Prior art date
Application number
PCT/US2007/075691
Other languages
English (en)
Inventor
David H. Shen
Ann P. Shen
Original Assignee
Nanoamp Solutions, Inc. (Cayman)
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 Nanoamp Solutions, Inc. (Cayman) filed Critical Nanoamp Solutions, Inc. (Cayman)
Priority to PCT/US2007/075691 priority Critical patent/WO2009023019A1/fr
Publication of WO2009023019A1 publication Critical patent/WO2009023019A1/fr

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B5/00—Generation of oscillations using amplifier with regenerative feedback from output to input
    • H03B5/30—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator
    • H03B5/32—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator being a piezoelectric resonator
    • H03B5/36—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator being a piezoelectric resonator active element in amplifier being semiconductor device
    • H03B5/366—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator being a piezoelectric resonator active element in amplifier being semiconductor device and comprising means for varying the frequency by a variable voltage or current
    • H03B5/368—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator being a piezoelectric resonator active element in amplifier being semiconductor device and comprising means for varying the frequency by a variable voltage or current the means being voltage variable capacitance diodes
    • 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
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B2200/00—Indexing scheme relating to details of oscillators covered by H03B
    • H03B2200/003—Circuit elements of oscillators
    • H03B2200/005—Circuit elements of oscillators including measures to switch a capacitor
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B2201/00—Aspects of oscillators relating to varying the frequency of the oscillations
    • H03B2201/02—Varying the frequency of the oscillations by electronic means
    • H03B2201/0208—Varying the frequency of the oscillations by electronic means the means being an element with a variable capacitance, e.g. capacitance diode
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B2201/00—Aspects of oscillators relating to varying the frequency of the oscillations
    • H03B2201/02—Varying the frequency of the oscillations by electronic means
    • H03B2201/025—Varying the frequency of the oscillations by electronic means the means being an electronic switch for switching in or out oscillator elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J2200/00—Indexing scheme relating to tuning resonant circuits and selecting resonant circuits
    • H03J2200/10—Tuning of a resonator by means of digitally controlled capacitor bank

Definitions

  • the present disclosure relates to circuitry, such as oscillators, for wireline and wireless communications.
  • Crystal oscillators are used frequently as a source of frequency stability for various communications systems.
  • the crystal is typically made of quartz and has resonating capabilities. Quartz is a material with piezoelectric properties that can be cut at certain angles and thicknesses to provide electrical and mechanical stability in radio frequency (RF) circuit designs.
  • RF radio frequency
  • a typical crystal oscillator can be manufactured to achieve tolerances of less than 10 ppm (parts per million), but larger tolerances tend to be less expensive to manufacture.
  • the crystal can be "tuned,” that is, adjusting the resonant frequency to a desired frequency through open-loop or closed-loop control in order to achieve tighter tolerances or to ease manufacturing requirements.
  • the crystal oscillator is an inherently stable resonator
  • this oscillator can be used in many types of electronic oscillator circuit topologies.
  • these oscillator circuit topologies can include the Colpitis, Hartley, and Pierce oscillator circuit topologies.
  • implementations can feature a method for tuning a frequency of a crystal oscillator that includes adjusting the tuning frequency of the crystal oscillator from a nominal frequency via a first switched-capacitor frequency tuning circuit.
  • the crystal oscillator includes an amplifier and a crystal, and the first switched-capacitor frequency tuning circuit is coupled to a first node of the crystal.
  • the first switched- capacitor frequency tuning circuit includes switchable sections to adjust the tuning of the crystal oscillator, and the switchable sections in the first switched-capacitor frequency tuning circuit includes an analog control input and a digital control input.
  • the method includes controlling the analog control input coupled to a node within each of the switchable sections, where each of the switchable sections in the first switched-capacitor frequency tuning circuit includes a fixed capacitor in series with a varactor and a switch.
  • the node within each of the switchable sections includes a node to control the varactor within each of the switchable sections.
  • the method includes controlling the digital control input, where the digital control input is configured to electrically connect or disconnect one or more of the switchable sections from the first node of the crystal.
  • the node to control the varactor within each of the switchable sections can be a common node in all of the switchable sections in the first switched-capacitor frequency tuning circuit.
  • the method can include receiving a multi-bit digital code on the digital control input to control the electrical connection or disconnection of each of the switchable sections, where each bit in the multi-bit digital code can be configured to control a connection or disconnection of the switch within one of the switchable sections in the first switched-capacitor frequency tuning circuit.
  • a ratio between the capacitance of the varactor to a capacitance of the capacitor can include a constant ratio for each switchable section in the first switched-capacitor frequency tuning circuit.
  • a total equivalent capacitance of the switched-capacitor frequency tuning circuit can be a function of the constant ratio.
  • the method can also include adjusting the tuning frequency of the crystal oscillator from a nominal frequency via a second switched-capacitor frequency tuning circuit that is coupled to a second node of the crystal.
  • the second switched-capacitor frequency tuning circuit can include switchable sections to adjust the tuning of the crystal oscillator.
  • Each of the switchable sections in the second switched-capacitor frequency tuning circuit can include a fixed capacitor in series with a varactor and a switch.
  • the switchable sections in the second switched- capacitor frequency tuning circuit can include the analog control input and the digital control input.
  • the method can include controlling the analog control input to each of the switchable sections in the second switched-capacitor frequency tuning circuit.
  • the analog control input can be coupled to a node within each of the switchable sections in the second switched-capacitor frequency tuning circuit.
  • the node within each of the switchable sections in the second switched-capacitor frequency tuning circuit can include a node to control the varactor within each of the switchable sections.
  • the method can involve controlling the digital control input, where the digital control input is coupled to the switch within each of the switchable sections in the second switched-capacitor frequency tuning circuit to electrically connect or disconnect one or more switchable sections from the crystal.
  • some implementations can feature a circuit for tuning a frequency of a crystal oscillator.
  • the circuit includes an oscillator circuit that includes an amplifier in parallel with a crystal.
  • the circuit has a first capacitor coupled to a first node of the crystal and a second capacitor coupled to a second node of the crystal.
  • the first and second capacitors are configured for nominal tuning of the crystal oscillator.
  • the circuit has a first switched-capacitor frequency tuning circuit coupled to the second node of the crystal, where the first switched-capacitor frequency tuning circuit includes switchable sections to adjust the tuning of the crystal oscillator.
  • the circuit includes an analog control input coupled to a varactor within each of the switchable sections.
  • the circuit includes a digital control input coupled to a switch within each of the switchable sections to electrically connect or disconnect one or more of the switchable sections from the second node of the crystal.
  • Each of the switchable sections can include a fixed capacitor in series with the varactor and the switch.
  • the analog control input can be configured to control the varactor within each of the switchable sections in the first switched-capacitor frequency tuning circuit.
  • the digital control input can be configured to carry a multi-bit digital code, where each bit in the multi-bit digital code can be configured to control an on or off position of the switch in one of the switchable sections in the first switched-capacitor frequency tuning circuit.
  • the digital control input can be configured to be independent of the analog control input.
  • a ratio between a capacitance of the varactor to a capacitance of the capacitor can involve a constant ratio for each switchable section in the first switched-capacitor frequency tuning circuit.
  • a total equivalent capacitance of the switched-capacitor frequency tuning circuit can be a function of the constant ratio.
  • a tuning sensitivity of the crystal can be a function of the constant ratio.
  • the circuit can also include a second switched-capacitor frequency tuning circuit coupled to the first node of the crystal, where the second switched-capacitor frequency tuning circuit can include switchable sections to adjust the tuning of the crystal oscillator.
  • the analog control input can be coupled to a varactor within each of the switchable sections in the second switched-capacitor frequency tuning circuit.
  • the digital control input can be coupled to a switch within each of the switchable sections in the second switched-capacitor frequency tuning circuit to electrically connect or disconnect one or more of the switchable sections from the first node of the crystal.
  • Each of the switchable sections in the second switched- capacitor frequency tuning circuit can include a fixed capacitor in series with the varactor and the switch.
  • the analog control input can be configured to control the varactor within each of the switchable sections in the second switched-capacitor frequency tuning circuit.
  • Each bit in the multi-bit digital code can be configured to control an on or off position of the switch in one of the switchable sections in the second switched-capacitor frequency tuning circuit.
  • a ratio between a capacitance of the varactor to a capacitance of the capacitor within the second switched-capacitor frequency tuning circuit can involve a constant ratio for each switchable section in the second switched-capacitor frequency tuning circuit.
  • some implementations can feature a system that has a crystal oscillator circuit, a first capacitor coupled to a first node of the crystal oscillator circuit, and a second capacitor coupled to a second node of the crystal oscillator circuit.
  • the system includes a first frequency tuning circuit to adjust a frequency of the crystal oscillator circuit, where the first frequency tuning circuit includes switchable sections, and each switchable section includes a capacitor in series with a switch and a varactor.
  • the system includes a digitally-controlled input coupled to each switch within each switchable section to control an electrical connection or disconnection of each switchable section in the first frequency tuning circuit to the second node of the crystal oscillator circuit.
  • the system also has an analogically-controlled input coupled to a commonly-shared node in all of the switchable sections in the first frequency tuning circuit.
  • the commonly-share node is configured to control the varactor within each of the switchable sections in the first frequency tuning circuit.
  • the digitally-control input can be independent of the analogically-control input.
  • a ratio between a capacitance of the varactor to a capacitance of the capacitor can be a constant ratio for each switchable section in the first frequency tuning circuit.
  • a total equivalent capacitance of the frequency tuning circuit can be a function of the constant ratio.
  • a tuning sensitivity of the crystal can include a function of the constant ratio.
  • the first and second capacitors can be inherent capacitances of the crystal itself.
  • the system can include a second frequency tuning circuit coupled to the first node of the crystal, where the second frequency tuning circuit can include switchable sections to adjust the frequency tuning of the crystal oscillator.
  • the analogically-controlled input can be coupled to a commonly-shared node in the switchable sections in the second frequency tuning circuit.
  • the commonly-share node can be configured to control the varactor within each of the switchable sections in the second frequency tuning circuit.
  • the digitally-controlled input can be coupled to a switch in each of the switchable sections in the second frequency tuning circuit to control an electrical connection or disconnection of one or more switchable sections in the second frequency tuning circuit from the first node of the crystal oscillator.
  • the system can include a receiver, transmitter, or transceiver, in which the crystal oscillator can couple into the receiver, transmitter, or transceiver.
  • the system can include other devices, where the crystal oscillator can couple with those devices.
  • Some of the devices may include computers, processors, clocks, radios, signal generators, counters, test and measurement equipment, function generators, oscilloscopes, phase-locked loops, frequency synthesizers, phones, wireless communication devices, and devices for the production and transmission of music and video.
  • the switches can be transmission gate switches.
  • the frequency tuning circuits can involve single-ended or fully-differential circuits.
  • some implementations can feature a method for manufacturing a frequency tuning circuit of a crystal oscillator.
  • the method involves forming the crystal oscillator by coupling an amplifier with a crystal.
  • the method includes forming a first switched-capacitor frequency tuning circuit that includes switchable sections to adjust the tuning of the crystal oscillator.
  • Each of the switchable sections in the first switched-capacitor frequency tuning circuit includes a fixed capacitor in series with a varactor and a switch.
  • the method includes coupling the first switched-capacitor frequency tuning circuit to a first node of the crystal, and coupling an analog control input to a node within each of the switchable sections.
  • the node within each of the switchable sections includes a node to control the varactor within the switchable sections.
  • the method involves coupling a digital control input to the switchable sections, where the digital control input is configured to electrically connect or disconnect one or more of the switchable sections from the first node of the crystal.
  • a ratio between a capacitance of the varactor to a capacitance of the fixed capacitor can include a constant ratio for the switchable sections in the first switched-capacitor frequency tuning circuit.
  • a total equivalent capacitance of the switched-capacitor frequency tuning circuit can be a function of the constant ratio.
  • the crystal can have capacitances that are inherent with the crystal in achieving a nominal tuning frequency.
  • the method can include coupling a second switched-capacitor frequency tuning circuit to a second node of the crystal, in which the second switched- capacitor frequency tuning circuit can include switchable sections to adjust the tuning of the crystal oscillator.
  • the switchable sections in the second switched-capacitor frequency tuning circuit can include a fixed capacitor in series with a varactor and a switch.
  • the method an include coupling the analog control input to a node within each of the switchable sections in the second switched-capacitor frequency tuning circuit.
  • the method can also involve coupling the digital control input to a switch within the switchable sections in the second switched-capacitor frequency tuning circuit to electrically connect or disconnect one or more switchable sections from the crystal.
  • additional switched-capacitor frequency tuning circuits can be coupled to the crystal oscillator for further tuning and adjustment.
  • Particular implementations may provide one or more following potential advantages.
  • the disclosed techniques facilitate precise frequency tuning of an electronic crystal oscillator that has a digital control and an analog control for frequency tuning.
  • Some advantages of the disclosed designs and techniques may include allowing a tuning range for the digital section of the oscillator tuning circuitry to be independently controlled from the analog section of the oscillator tuning circuitry. By having independent control between the digital and analog tuning mechanisms, the digital tuning selections do not have to impact the analog tuning range and vice-versa.
  • the independent control can also improve tuning range variations and sensitivities over conventional analog and digital tuning techniques.
  • tuning ranges can be maintained constant for the crystal oscillator by keeping a ratio of varactor capacitance to fixed capacitance constant using capacitors in tank circuits, where the tuning ranges can be adjusted via a switched capacitor network of capacitors and varactors.
  • Another potential advantage includes not requiring exact matching of the capacitances between the fixed capacitors and varactors for the tuning circuit.
  • the disclosed designs can be differential designs that can reduce spurious noise.
  • An additional benefit of the disclosed designs involves producing fine and precise tuning ranges of the crystal oscillator by implementing segments of capacitors and varactors in one or more tunable switched capacitor networks where the capacitances of the capacitors and varactors within each segment can differ from each other within and/or among the tunable switched capacitor networks.
  • the oscillator can be tuned by varying one or more parameters of multiple frequency tuning options, such as by varying the capacitance of the segments, varying a number of connected segments, varying the on and off switching ratios, varying a number of switched capacitance networks in series, and varying the values of V DAFC and/or V AFC -
  • the disclosed designs provide the additional potential benefits of having multiple and/or concurrent degrees of freedom to tune the frequency of the crystal oscillator.
  • Fig. 1 is a model of a crystal device as a passive L and C network.
  • Fig. 2 shows a model of a conventional crystal oscillator circuit.
  • Fig. 3 is a model of a conventional digitally-controlled crystal oscillator.
  • Fig. 4 is an example embodiment of the disclosed tuning technique.
  • Fig. 5 is an example embodiment of the disclosed tuning technique.
  • Fig. 6 is an example embodiment of the disclosed tuning technique.
  • Like reference numbers and designations in the various drawings indicate like elements.
  • Fig. 1 shows a simplified model 100 of the crystal device as a passive L and C network, with capacitor elements Cl 110, Co 120, and inductor element L 115.
  • Capacitor Co 120 represents the parallel plate capacitance, such as the capacitance from wires and contacts.
  • Capacitor Cl I lO and inductor L 115 represent the energy storage units in the model. Since the quartz crystal has a high Q value, the series capacitance Cl 110 is very low and the series inductance L 115 is very high.
  • the resonant frequency of the crystal can be "pulled" by adding parallel and/or series resonant components, such as capacitors as loads to the resonant circuit.
  • the pulling can be done, for example, through analog controlling a variable capacitor device (varactor) or through digital means via tuning a weighted array of capacitor.
  • Fig. 2 shows a model 200 of a conventional crystal oscillator circuit.
  • Fig. 2 shows an example where the resonant frequency of the crystal can be "pulled” through analog control of a variable capacitor device, varactor 217.
  • an inverting amplifier 213 is put in parallel with a crystal 215 to form a crystal oscillator circuit.
  • the parallel load capacitors 211 and 212 are used to set a nominal fixed frequency of the resonant circuit.
  • the varactor 217 is tuned by an analog control voltage 220, V AFC> which is used to tune the frequency of the crystal oscillator.
  • the varactor 217 is coupled to the crystal 215 through a capacitor 219.
  • Fig. 3 shows a model 300 of a conventional crystal oscillator circuit.
  • Fig. 3 shows an example where the resonant frequency of the crystal can be "pulled" through digital means by tuning a weighted array of capacitors.
  • An advantage of using digital control (e.g., Fig. 3) in contrast with analog control (e.g., Fig. 2) is that the digital control circuits can be more easily implemented and integrated into an overall integrated circuit system, especially for circuit implementations using digital process technologies.
  • the digitally-controlled frequency tuning design may be referred to as a digitally-compensated crystal oscillator (DCXO).
  • DCXO digitally-compensated crystal oscillator
  • Fig. 3 has amplifier 213 in parallel with the crystal 215.
  • a digitally programmable switched-capacitor array 329 has capacitors 324 and switches 323.
  • the array 329 can be a tunable load that is in parallel with load capacitors 325, 327.
  • the switches 323 in the array 329 are controlled by a switch control circuit 350.
  • a single-ended load is shown in the example embodiment of Fig. 3, either a single-ended or differential load can be used.
  • large devices need to be used to obtain good matching amongst the switches 324.
  • the example embodiment of Fig. 3 can also require complex calibration schemes to reduce mismatch. As a result, there can be a substantial amount of die area and/or complexity required to obtain a good digital-bit resolution in conventional designs.
  • circuits can be combined to tune a crystal oscillator with both a digital control and an analog control to achieve higher resolutions (e.g., higher than 10 bits of resolution).
  • the analog and digital controls are not independent of each other.
  • one type of control e.g., analog control
  • another other type of control e.g., digital control
  • Conventional tuning circuits can have a wide variation in tuning ranges because the digital tuning circuit can adversely impact the analog tuning range and vice-versa. This adverse impact can force a substantial uncertainty in the tuning ranges and can also lead to difficulty in process variation control.
  • the interactions between conventional analog and digital controls can require higher resolution tuning controls in order to meet minimum and maximum tuning ranges and step sizes for frequency tuning.
  • Fig. 4 is an example embodiment of a model 400 for a disclosed tuning technique.
  • the inverting amplifier 213 is in parallel with the crystal 215, and the capacitor loads 211 and 212 are fixed tuning capacitor loads to be used to set the nominal oscillator frequency.
  • a switched capacitor network 425 includes varactors 431 , tuning capacitors 432 and switches 433.
  • the switches 433 are controlled by the digital signal V DAFC 330 to on or off positions to connect or disconnect both the varactors 431 and the capacitors 432.
  • the digital signal V DAFC 330 can have a multi-bit digital code to set the on or off positions of the switches 433.
  • the switched capacitor network 425 couples to a load capacitor 212 to tune the crystal oscillator.
  • An analog control V A F C 220 is connected to a node between respective varactors 431 and capacitors 432 to tune the varactors 431 and capacitors 432 independently of the digital control VD A F C -
  • the analog control V A F C 220 can be used to adjust the capacitance for respective varactors 431.
  • the ratio between the capacitance of the varactors 431 to the capacitance of the capacitors 432 can be maintained at a constant ratio, regardless of the digital code of the digital signal VD A F C 330. This constant ratio for the capacitance can maintain the independence of the analog control range and the digital control range.
  • the ratio for the capacitance can be expressed by equations relating to series and parallel capacitance networks.
  • a given switchable section of the switched-capacitor network can have a fixed value, C f1x
  • the varactor can have a variable capacitance range value of Cva r - Fig. 4, for example, shows an embodiment where each switchable section 435 of the switched-capacitor network 425 includes a capacitor 432 in series with a varactor 431 and a digitally-controllable switch 433.
  • each switchable section i can be expressed as a bit in the digital signal VD A F C 330.
  • a total capacitance for the switchable section i can expressed by the equation
  • the capacitance values of C var j and, in part, C a tio n .; are functions of V A F C 220.
  • the total load capacitance of the network 425 can be expressed as n
  • the multi-bit digital code can adjust the value of k, to generate a load capacitance, C L 1 , such that the crystal resonant frequency is tuned to the correct oscillating frequency.
  • the value of k can be a function of V DAFC 330.
  • k can be expressed as an average ratio of on-to-off switching of a switchable segment i.
  • the total load capacitance C L-1 can vary by the same percentage ratio over the analog tuning range of values, which can be set, in part, by the varactor capacitance C var _i-
  • the analog tuning range can be preserved relatively independent of the digital code that is used to coarse tune the resonant frequency of the crystal oscillator.
  • the oscillator frequency can be tuned by varying one or more of multiple tuning parameters, such as by varying the capacitance of the segments, varying the number of connected segments, and varying the values of V DAFC 330 and/or V AFC 220.
  • Fig. 5 shows an example embodiment of a model 500 for a disclosed tuning technique.
  • the inverting amplifier 213 is placed in parallel with crystal 215.
  • the fixed load capacitors 211 and 212 can provide a nominal tuning of the oscillator frequency.
  • a switched capacitor network 545 includes varactors 541, tuning capacitors 542, and switches 543.
  • the switches 543 are controlled by the digital signal VD AF C 330 to on or off positions to connect or disconnect the varactors 541 and the capacitors 542.
  • the digital signal VD AF C 330 can have a multi-bit digital code to set the on or off positions of the switches 543.
  • An analog control V AF C 220 is connected to a node between respective varactors 541 and capacitors 542 to tune the varactors 541 and capacitors 542 independently of the digital control VD AF C 330.
  • the switched capacitor network 545 couples to load capacitor 211 to tune the crystal oscillator.
  • Fig. 6 shows an example embodiment of a model 600 for the disclosed tuning technique. In the embodiment of Fig. 6, the inverting amplifier 213 is placed in parallel with crystal 215. The fixed load capacitors 211 and 212 can provide a nominal tuning of the oscillator frequency.
  • Fig. 6 has two switch capacitor networks 425, 545.
  • Switched capacitor network 545 includes varactors 541 , tuning capacitors 542, and switches 543.
  • the switches 543 are controlled by the digital signal VD A FC 330 to on or off positions to connect or disconnect the varactors 541 and the capacitors 542.
  • the digital signal V DAF C 330 can have a multi-bit digital code to set the on or off positions of the switches 543.
  • An analog control V AF C 220 couples through a resistor 672 to a node between respective varactors 541 and capacitors 542 to tune the varactors 541 and capacitors 542 independently of the digital control VD A FC 330.
  • the switched capacitor network 545 couples to load capacitor 211 to tune the crystal oscillator.
  • Switched capacitor network 425 includes varactors 431 , tuning capacitors 432, and switches 433.
  • the switches 433 are also controlled by the digital signal VD AF C 330 to on or off positions to connect or disconnect the varactors 431 and the capacitors 432.
  • the digital code of the digital signal VD AF C 330 can set the positions of the switches 433.
  • the analog control V AF C 220 couples though a resistor Rl 674 to a node between respective varactors 431 and capacitors 432 to tune the varactors 431 and capacitors 432 independently of the digital control VDAFC-
  • the switched capacitor network 425 couples to a load capacitor 212 to tune the crystal oscillator.
  • Fig. 6 shows two switched capacitor networks 425, 545 that are separated by resistors 672, 674 on one end. The resistors 672, 674 can prevent charge-sharing between the two networks 425, 545.
  • a load capacitance can be generated similar to Fig. 4 for each network 425, 545.
  • networks 425, 545 are in series in Fig. 6.
  • the model 600 of Fig. 6 can be extended to include more than two switched capacitor networks.
  • the oscillator can be tuned to varying amounts of resolutions, including finer resolutions.
  • the values of the fixed capacitances can vary between and/or within their switched capacitor networks.
  • the value of kj can represent the average on and off switching ratio for switchable segment i, and can vary between segments within a switched capacitor network.
  • C f , x _i and C va ⁇ j can have the same capacitances for each switchable segment i in a network, but the average on and off switching ratio can be increased by a factor of r for consecutive segments, where r > 1.
  • the total load capacitance of the network can be scaled by a factor of (rM)/(r-l).
  • the scaling factor of (1-0/(1 -r) may be obtained if r ⁇ 1.
  • the total load capacitance of the network can be scaled by a factor of (rM)/(r-l).
  • the total load capacitance of the network can be scaled by a factor of 2 n -l.
  • the scaling factor of (l-r ⁇ l-r) may be obtained if r ⁇ 1.
  • the capacitance values of C f i x j and C va r_ > are increased by a factor of s for each consecutive segment and the average on and off switching ratio is increased by a factor of r for consecutive segments (for r > 1), then the total load capacitance of the network can be increased by a factor of ((r*s) n -l)/(r*s-l).
  • the scaling factor is (4 n -l)/3. In other embodiments, the scaling factor of ((r*s) n -l)/(r*s-l) maybe obtained if r ⁇ 1 or s ⁇ 1.
  • the example embodiments of Figs. 4-6 can be implemented in fully-differential designs. The fully-differential designs can provide the benefits of improved performance by reducing spurious noise even further than the example embodiments shown in Figs. 4-6.
  • the disclosed techniques can be used with oscillators for many systems, including wireless communication systems.
  • the disclosed techniques can be used with oscillators for receivers and transceivers, such as the receiver and transceiver architectures for superheterodyne receivers, image-rejection (e.g., Hartley, Weaver) receivers, zero-intermediate frequency (IF) receivers, low-IF receivers, direct-up transceivers, two-step up transceivers, and other types of receivers and transceivers for wireless and wireline technologies.
  • image-rejection e.g., Hartley, Weaver
  • IF zero-intermediate frequency
  • low-IF receivers zero-intermediate frequency
  • direct-up transceivers two-step up transceivers
  • other types of receivers and transceivers for wireless and wireline technologies.
  • the disclosed techniques can be used with crystal oscillators that are coupled in devices, such as computers, processors, clocks, radios, signal generators, counters, test and measurement equipment, function generators, oscilloscopes, phase-locked loops, frequency synthesizers, phones, wireless communication devices, and devices for the production and transmission of music and video.
  • the switches can be transmission gate switches.

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  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Oscillators With Electromechanical Resonators (AREA)

Abstract

La présente invention concerne dans des modes de réalisation, des techniques et des systèmes de réglage analogique et numérique d'oscillateurs cristallins. Dans un aspect de l'invention, certaines implémentations proposent un procédé de réglage de la fréquence d'un oscillateur cristallin qui peut inclure l'ajustement de la fréquence de réglage de l'oscillateur cristallin à partir d'une fréquence nominale via un circuit de réglage de fréquence à condensateur commuté, ce circuit pouvant disposer de sections commutables pour ajuster le réglage de l'oscillateur cristallin. Le procédé peut comprendre le contrôle d'une entrée de contrôle analogique qui est couplée à un varacteur dans chacune des sections commutables où chacune des sections commutables peut comprendre un condensateur fixé en série avec le varacteur et un commutateur. Le procédé peut impliquer le contrôle d'une entrée de contrôle numérique où l'entrée de contrôle numérique peut électriquement connecter ou déconnecter une ou plusieurs des sections commutables à partir du cristal. Il peut exister un contrôle indépendant entre les mécanismes de réglage numériques et analogiques.
PCT/US2007/075691 2007-08-10 2007-08-10 Circuit de réglage de fréquence d'oscillateur cristallin WO2009023019A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/US2007/075691 WO2009023019A1 (fr) 2007-08-10 2007-08-10 Circuit de réglage de fréquence d'oscillateur cristallin

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2007/075691 WO2009023019A1 (fr) 2007-08-10 2007-08-10 Circuit de réglage de fréquence d'oscillateur cristallin

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WO2009023019A1 true WO2009023019A1 (fr) 2009-02-19

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5874864A (en) * 1996-11-06 1999-02-23 Matsushita Electric Industrial Co., Ltd. Crystal oscillating device and method of adjusting said crystal oscillating device
US6788159B2 (en) * 2001-10-09 2004-09-07 Nippon Precision Circuits Inc. Temperature compensated oscillator, adjusting method thereof, and integrated circuit for temperature compensated oscillator

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5874864A (en) * 1996-11-06 1999-02-23 Matsushita Electric Industrial Co., Ltd. Crystal oscillating device and method of adjusting said crystal oscillating device
US6788159B2 (en) * 2001-10-09 2004-09-07 Nippon Precision Circuits Inc. Temperature compensated oscillator, adjusting method thereof, and integrated circuit for temperature compensated oscillator

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