GB1596845A - Quartz crystal resonator - Google Patents
Quartz crystal resonator Download PDFInfo
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- GB1596845A GB1596845A GB4906277A GB4906277A GB1596845A GB 1596845 A GB1596845 A GB 1596845A GB 4906277 A GB4906277 A GB 4906277A GB 4906277 A GB4906277 A GB 4906277A GB 1596845 A GB1596845 A GB 1596845A
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- 239000013078 crystal Substances 0.000 title claims description 90
- 239000010453 quartz Substances 0.000 title claims description 52
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims description 52
- 238000012937 correction Methods 0.000 claims description 34
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- 230000007306 turnover Effects 0.000 description 1
Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L1/00—Stabilisation of generator output against variations of physical values, e.g. power supply
- H03L1/02—Stabilisation of generator output against variations of physical values, e.g. power supply against variations of temperature only
- H03L1/022—Stabilisation of generator output against variations of physical values, e.g. power supply against variations of temperature only by indirect stabilisation, i.e. by generating an electrical correction signal which is a function of the temperature
- H03L1/027—Stabilisation of generator output against variations of physical values, e.g. power supply against variations of temperature only by indirect stabilisation, i.e. by generating an electrical correction signal which is a function of the temperature by using frequency conversion means which is variable with temperature, e.g. mixer, frequency divider, pulse add/substract logic circuit
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- Oscillators With Electromechanical Resonators (AREA)
Description
(54) QUARTZ CRYSTAL RESONATOR
(71) We, HEWLETT-PACKARD COMPANY, a company organised and existing under the laws of the State of California, United States of America, of 1501 Page Mill
Road, Palo Alto, California 94304, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:
This invention is concerned with improvements in or relating to quartz crystal resonators.
The resonant frequency of a quartz crystal is dependent on the elastic coefficients, the density, the thickness and overtone operation of the crystal. In addition, each of these factors varies with changes in the ambient temperature of the crystal, and, thus, resonant frequency variations occur.
Conventional methods for making the frequency of a quartz crystal resonator minimally dependent on temperature variations include three approaches. The first approach utilizes a heated oven to control the ambient temperature of the crystal resonator and thus control the frequency of that crystal. To further improve the frequency-temperature performance, the crystal resonator will typically be cut in one of the thermally compensated orientations for which the crystal resonator has inherently good frequency stability over a narrow temperature range. Two widely used singly rotated orientations are the AT and BT.
This approach generally yields crystal resonator controlled oscillators exhibiting the highest frequency stability currently obtainable. However, this approach experiences three potential drawbacks. First, in modern crystal resonator controlled applications the oven will be the predominant power user. Second, a thermal stabilization time of many minutes is required when the crystal oven is first turned on even when available power is not limited.
A large portion of this time is necessary to allow thermal gradients in the resonator to equilibriate and thus the advantage of instant warm up of transistor circuits is lost. Third, optimum temperature control of the quartz resonators is not possible unless the actual temperature of the quartz plate is known. Because the thermal sensing element is not in intimate contact with the resonator errors in ambient control degrade frequency stability.
The second and third approaches utilize temperature compensation without the use of the oven. VCXO's (Voltage Controlled Crystal Oscillators) and TCXO's (Temperature
Controlled Crystal Oscillators) represent the second approach. The VCXO typically includes a combination of a crystal resonator, an amplified, and a voltage variable phase shifter. The voltage which is applied to the variable phase shifter represents a feed-back signal derived from some form of temperature sensor, usually a thermistor or thermistor bridge, although more elaborate methods are possible.
The TCXO includes in the crystal resonator feed-back path carefully selected reactive components which are not voltage variable, but which have a temperature-characteristic response which exactly compensates for the temperature behavior of the crystal resonator resulting in a device exhibiting a minimal frequency-temperature dependence.
The third approach utilizes novel characteristics of crystal resonators to obtain temperature compensation without the use of an oven. U. S. Patent Specification No.
3,826,931 describes a resonator apparatus which utilizes either a single quartz crystal vibrating in two selected modes or two quartz crystals each vibrating in a single selected mode to form a resonator output frequency that is the sum or difference of the two crystal frequencies and is minimally temperature dependent.
All three approaches experience a significant drawback. The temperature compensation described is static compensation, that is, temperature compensation is achieved only under conditions where the ambient temperature is slowly changing. Rapidly changing temperatures sufficient to cause thermal gradients through the crystal resonator, cause instantaneous frequency shifts orders of magnitude greater than the static stability of the device.
For example, the AT cut resonator in an oven an have short term stabilities which are several parts in 1010. However, a 1"C temperature gradient through the crystal resonator can cause a sudden frequency shift of 36 parts in 106.
Dynamic compensation for thermal transients was recently discovered by Richard
Holland. He predicted a doubly-rotated crystal resonator cut, the TS, that has an orientation of (yxwl) 22.80/34.30 (ANSI C83.3 - 1951 (R1972)) which exhibits inherently good frequency stability over a narrow temperature range suitably for obtaining good static compensation using either of the first two approaches discussed previously, and at the same time was inherent dynamic compensation for temperature transients. The TS orientation was introduced by Richard Holland in the following publications:
Richard Holland, "Nonuniformly Heated AnisotroicPlates: I. Mechanical Distortion and Relaxation", IEEE Transactions on Sonics and Ultrasonics, Vol.SU-21, July 1974, pp.
171-178, and Richard Holland, "Nonuniformly Heated Anisotropic Plates: II. Frequency
Transients in AT and BT Quartz Plates", 1974 Ultrasonics Symposium Proceedings, IEEE
Cat. # 74CHO 896-15U, pp.592-598.
At essentially the same time, another doubly-rotated crystal resonator cut, the SC, was predicted by Earl EerNisse to be (yxwl) 22.50/34.30, which is essentially the same as that predicted by Richard Holland. The SC orientation was introduced by Earl EerNisse in the following publication:
Earl EerNisse, "Quartz Resonator Frequency Shifts Arising from Electrode Stress",
Proceedings of the 29th Annual Symposium on Frequency Control 1975, U. S. Army
Electronics Command, Fort Monmouth, N.J., 28-30 May 1975 pp 1-4.
This cut exhibits the necessary frequency-temperature stability over narrow temperature ranges to obtain good static compensation with either the first or second approach. In addition, the SC is claimed to be frequency independent of internal stresses in the crystal resonator caused by deposited electrode patterns, crystal resonator mounts, and externally applied stress in the plane of the crystal resonator surface. Both of these orientations offer thermal and mechanical stress sensitivity improvements over the AT and BT orientations but they still require operation in a controlled temperature environment over a narrow temperature range to achieve good frequency stability.
The present invention provides signal generation apparatus comprising: a quartz crystal resonator having a selected crystallographic orientation that is equal to (yxwl) 21.93 /33.93 + 2" for providing static and dynamic thermal transient compensation, and having first and second thickness modes of vibration in response to an electric field applied thereto, vibration in each of said modes being characterized by a selected frequency-temperature deviation characteristic; means for generating and supplying said electric field to said quartz crystal resonator and for isolating the first and second frequency signals of said first and second modes of vibration, respectively; and compensation means coupled to receive said first and second freqency signals for generating an output signal that is relatively independent of any temperature induced deviations of said first and second frequency signals, one of said first and second frequency signals received by the compensation means being representative of the temperature of said quartz crystal resonator and used to generate an intermediate signal used in the generation of the output signal.
In an apparatus as set forth in the last preceding paragraph, it is preferred that said one of the first and second frequency signals and its corresponding thickness mode of vibration comprises the B mode frequency signal and its B mode of vibration of the quartz crystal resonator each having a predominantly linear frequency-temperature characteristic over a selected temperature range; and said other of the first and second frequency signals and its corresponding thickness mode of vibration comprises the C mode frequency signal and its C mode of vibration of the quartz crystal resonator each having a predominantly third order frequency-temperature characteristic over a selected temperature range.
In an apparatus as set forth in the last preceding paragraph, it is preferred that said compensation means comprises: input means coupled to said electric field generating and supplying means or receiving at least the B mode frequency signal of said B and C mode frequency signals and for providing a third signal whose frequency is representative of the internal temperature of the quartz crystal resonator; counter means coupled to receive, and for counting the frequency of said third signal and generating a fourth signal with an encoded value that is representative of the counted frequency value of the third signal; and processor means coupled to receive said fourth signal for producing therefrom a fifth signal with an encoded value that is a function of the temperature of the quartz crystal resonator.
the fifth signal being said intermediate signal.
In an apparatus as set forth in the last preceding paragraph, said processor means may produce the fifth signal by a curve fitting technique or by a look-up table and interpretation technique.
In an apparatus as set forth in the last preceding paragraph but one, it is preferred that said counter means is further coupled to receive an unknown frequency signal from an external signal source for counting the frequency of the unknown signal and for generating a sixth signal with an encoded value that is representative of the counted frequency value of the unknown signal, said C mode frequency signal also being coupled to the counter means to provide a time base reference signal for the counting of the frequency of both the third and the unknown frequency signals; said fifth signal has an encoded value that is representative of a correction factor to the measured value of the frequency of the unknown signal using the temperature sensitive C mode frequency signal; and said processor means is further coupled to receive the sixth signal for algebraically combining the encoded values of the fifth and sixth signals to form a value to be encoded into the output signal, said encoded value of the output signal being representative of an accurate measure of the frequency of the unknown signal corrected for the temperature-frequency deviation of the C mode frequency.
In an apparatus as set forth in the last preceding paragraph, it is preferred that said compensation means further includes display means coupled to receive the output signal for displaying its encoded value.
In an apparatus as set forth in the last preceding paragraph but three, said processor means includes means for subtracting from the encoded value of the fourth signal a value that is representative of an encoded value of the fourth signal where the C mode frequency is within a selected accuracy of a pre-selected output signal frequency forming from the subtraction result a sixth signal, from the sixth signal the processor means generates the fifth signal, said fifth signal having an encoded value representative of a correction factor necessary to shift the C mode frequency to maintain the output signal within the selected accuracy; and said compensation means further comprises rate multiplier means having clock and rate input ports being coupled to receive the C mode frequency signal and the fifth signal, respectively, and wherein an output signal is generated having a frequency that corresponds to the C mode frequency shifted in response to the fifth signal, said output signal having a frequency within the selected accuracy.
The present invention further provides a method of generating a signal, said method
comprising the steps of: exciting a quartz crystal resonator having a selected crystallog
raphic orientation that is equal to (yxwl) 21.93 /33.93 + 2" for providing static and dynamic thermal transient compensation into simultaneous vibration in a first and a second
independent thickness mode of vibration, vibration in each of said modes being
characterized by a selected frequency-temperature deviation characteristic; isolating from
each other a first and a second frequency signal corresponding to the first and the second
mode of vibration respectively; and generating from said first and second frequency signals
an output signal that is relatively independent of any temperature induced deviations of said
first and second frequency signals, on of said first and second frequency signals utilized in
the generation of the output signal being representative of the temperature of said quartz
crystal resonator and used to generate an intermediate signal used in the generation of the
output signal.
In carrying out a method as set forth in the last preceding paragraph, it is preferred that
said one of the first and second frequency signals and its corresponding thickness mode of
vibration comprises the B mode frequency signal and its B mode of vibration of the quartz
crystal resonator each having a predominantly linear frequency temperature characteristic
over a selected temperature range; and said other of the first and second frequency signals
and its corresponding thickness mode of vibration comprises the C mode frequency signal
and its C mode of vibration of the quartz crystal resonator each having a predominantly
third order frequency-temperature characteristic over a selected temperature range.
In carrying out a method as set forth in the last preceding paragraph, it is preferred that
the step of generating an output signal includes: producing a third signal whose frequency is
representative of the internal temperature of the crystal resonator from at least one of the B
and C mode frequency signals; counting the frequency of the third signal and generating a
forth signal with an encoded value that is representative of the counted frequency value of
the third signal; and processing the fourth signal to produce a fifth signal with an encoded
value that is a function of the temperature of the quartz crystal resonator the fifth signal
being said intermediate signal.
In carrying out a method as set forth in the last preceding paragraph, it is preferred that
the step of processing the fourth signal includes: predetermining and storing coefficients of
an nth other polynomial that is a function of the encoded value of the fourth signal to
accurately produce the encoded value of the fifth signal over the entire selected temperature range; and algebraically combining the encoded value of the fourth signal with the stored coefficients of the nth order polynomial to form the encoded value of the fifth signal.
In carrying out a method as set forth in the last preceding paragraph, but one it is preferred that the step of processing the fourth signal includes: predetermining the values to be encoded in each of the fourth and fifth signals with the quartz crystal resonator operating at a plurality of selected temperatures; prestoring the individual predetermined values to be encoded in the fifth signal in a storage device with the corresponding predetermined values of the fourth signal as pointers thereto; applying the actual encode value of the fourth signal to the storage device; identifying a plurality of pointers having values between which the actual encoded value of the fourth signal falls; and interpolating between the stored values to be encoded into the fifth signal corresponding to said plurality of pointers utilizing the plurality of pointers and the actual value encoded in the fourth signal; said plurality of pointers being a signal pointer when there is agreement between the actual encoded value of the fourth signal and one of the stored pointers wherein the value to be encoded in the fifth signal is the stored value corresponding to said single pointer.
In carrying out a method as set forth in the last preceding paragraph but two, it is preferred that the step of generating an output signal further includes the steps of: utilizing the C mode frequency signal as a time base reference for counting the frequency of other signals; counting the frequency of an externally applied unknown frequency signal and generating a sixth signal with an encoded value that is representative of the counted frequency value of the unknown frequency signal using the temperature sensitive C mode frequency signal; and algebraically combining the encoded values of the fifth and sixth signals forming a value to be encoded into the output signal, the encoded value of the output signal being representative of an accurate measure of the frequency of the unknown signal, the encoded value of said fifth signal being a correction factor to the encoded value of the sixth signal.
In carrying out a method as set forth in the last preceding paragraph but three, it is preferred that the step of processing the fourth signal includes the steps of: subtracting from the encoded value of the fourth signal a value that is representative of an encoded value of the fourth signal where the C mode frequency is within a selected accuracy of a preselected frequency to form a sixth signal having an encoded value equivalent to the result of the subtraction; converting the encoded value of the sixth signal into a value representative of a correction factor necessary to shift the C mode frequency to maintain this frequency within the selected accuracy of the preselected frequency; and encoding the C mode frequency correction factor value into the fifth signal; and the step of generating an output signal further includes the step of shifting the frequency of the C mode signal in response to the fifth signal to produce the output signal having the preselected frequency within the selected accuracy.
In the first illustrated embodiment of the invention, the frequency of the thermometer signal, or a linear combination of this signal and the reference frequency signal, e.g. the ratio or difference of these signals, is measured against the reference frequency signal. The signal representative of this measured value is then applied to a processor which determines the temperature of the quartz crystal resonator by means of a curve-fitting or look-up table interpolation routine. This embodiment is easily expanded to also measure the unknown frequency of an external signal against the reference frequency signal. A signal representative of this measured value is then transferred to the processor with the signal representative of the crystal temperature.The processor utilizes the temperature signal to determine the correction factor to be applied to the measured value of the unknown frequency made necessary by any temperature induced shift of the reference frequency.
The correction factor is then applied to the signal corresponding to the measured value of the unknown frequency. Either the curve-fitting or the look-up table interpolation routine, mentioned above, is utilized in this application to generate the correction factor.
The second illustrated embodiment of this invention utilizes a similar approach to stabilize one of the mode frequencies against temperature induced frequency variations. As in the first embodiment, the frequency of the thermometer signal, whether it is the corresponding mode signal or a combination of both signals, is measured. Should the frequency measurement subsystem require a reference frequency, this reference frequency can be the second mode signal whose frequency is to be stabilized. The measured value of the thermometer signal is then applied to a processor wherein, as discussed above, a correction factor to the mode signal to be stabilized is generated. This correction factor signal and the mode signal to be stabilized are both then applied to a rate multiplier to generate a resultant output signal that is the stabilized frequency signal.
In the third illustrated embodiment of the present invention, the quartz crystal resonator is enclosed within an oven to stabilize the frequency of the reference frequency mode signal. This is accomplished by using the thermometer signal from the crystal in the same manner as in the second embodiment to determine a correction factor signal that is representative of the offset of the oven temperature from a preselected temperature above room temperature. This correction factor signal together with a fixed signal that is representative of the preselected whose output signal is the input power signal to the oven for maintaining the preselected temperature within the oven.
There now follows a detailed description which is to be read with reference to the accompanying drawings of embodiments of the present invention; it is to be clearly understood that these embodiments have been selected- for description to illustrate the invention by way of example only.
In the accompanying drawings:
Figure 1 is a plot of the frequency deviation versus temperature for the B and C mode frequencies of a quartz crystal resonator of the (yxwl) 21.93 /33.93 orientation;
Figure 2a-d are block diagram representations of a variety of oscillator implementations wherein the included quartz crytal resonator is excited to vibrate in two thickness modes simultaneously;
Figure 3 is a block diagram of a first embodiment of the present invention wherein the quartz crystal resonator with an open loop compensation network is used to accurately measure the frequency of an unknown signal; and
Figure 4 is a block diagram of a second embodiment of the present invention wherein the quartz crystal resonator with an open loop compensation network is used as a stable frequency source;
Investigations have shown that by using a crystal oriented within two degrees of (yxwl) 21.93 /33.93 and operating in the slow hear or C mode of the thickness operation the crystal resonator is both statically and dynamically thermally compensated in the region of the crystal turnover temperature. This central can be referred to as being a TTC (Thermal
Transient Compensated) type. It is widely known that the frequency-temperature behavior of any precision cut quartz resonators can be well represented by a power series expansion.
A crystal of the above orientation has a frequency-temperature curve wherein the contribution of the fourth and higher order terms is typically less than one part in 108, over a temperature range of two hundred degrees Celcius. The shape of this curve can be expressed algebraically as:
f = f0 [1 + aT + bT2 + cT3] (1)
where f0 is the resonant frequency at a selected reference temperature, a, b, and c
are first, second and third order temperature coefficients of,frequency, and T is the
value of the actual crystal temperature minus the value of the selected reference
temperature.
It is well known that crystal orientations exist for which a single crystal can be driven to cause the crystal to vibrate in a plurality of thickness modes simultaneously. This is possible since the three thickness modes of motion are orthogonal and can exist simultaneously without mutually interfering with each other.
Figure 1 shows a representative plot of the temperature-frequency deviation of the B (fast shear) and C (slow shear) modes of a quartz resonator of the (yxwl) 21.93 /33.93 orientation. These temperature-frequency deviation curves show that the B mode frequency variation is predominantly linear and the C mode frequency variation is predominantly third order over the 70" Celsius range of Figure 1. The frequency variations are approximately 1900 PPM (parts per million) for the B mode frequency and 25 PPM for the C mode frequency.
In a crystal resonator of this type, the B mode frequency variations can be used to sense the plate temperature of the crystal and thus provide a means whereby errors caused by the temperature sensitivity of the C mode frequency can be corrected when the C mode frequency is used as a frequency or time base reference or a frequency source.
Any of these applications can be achieved by utilizing a curve fitting routing, or a look-up table and interpolation. In either of the curve fitting or look-up table implementations, the initial step is to measure both the B and C mode frequencies at selected temperatures over the required operating range. These values can then be used to either derive the coefficients of the selected curve fitting expression, or to determine individual entries for a look-up table at each of the selected temperatures.
In a curve fitting implementation, the C mode frequency signal of the resonator can be used as the time base signal for measuring the frequency value of a second selected frequency signal.
Since the C mode frequency varies with temperature variations, the measured frequency will be incorrect. The relative error of the measured signal can be defined as:
where f, is the measured value of the selected frequency signal and fst is the true value of the same signal. The true value of this signal can be expressed as
By means of known frequency counter principles (Hewlett-Packard Company Application Note 172), the relative error of the C mode frequency signal is equivalent to of and can be expressed as:
where fc is the frequency value of the C mode signal at the operating temperature of
the TTC crystal and fco is the selected reference frequency of the C mode frequency
signal.
The actual frequency of the C mode time base can be expressed as a polynomial in temperature as:
fc = fco (1 + AcT + BcT2 + CcT3 + ... ) (5) where Ac, Bc, Cc ..., are the first, second, third ..., order temperature coefficients of frequency and T is normalized temperature.By substituting fc of
equation (5) into equation (4), the error expression becomes
of = ACT + BCT2 + CCT3 + .. (6)
The resultant value from equation (6) can then be inserted into equation (3) to determine the true frequency of the selected frequency signal, or to stabilize the frequency of the C mode frequency by performing the following calculation:
Therefore, by knowing the appropriate coefficients and the normallized temperature. T, the correction factor can be computed and either equation (3) used to derive the correct measured frequency, or equation (4) used to correct the system output frequency.
The TTC crystal has essentially a built-in thermometer in the B-mode response. This is predominantly a linear T.C. mode with a slope large enough to that fB-fC (the difference in the two mode frequencies) is always positive and single valued.
In the proposed implementation, the true B-mode frequency, fBT, can be measured using the actual C-mode frequency, fc, as a time base. This of course gives rise to an error in the measured frequency, fa. The relative error again is identical and is given by:
After selecting a reference frequency, fco, we can measure fn and fc as a function of temperature using a precision time base, and then construct a table of the apparent if measured with fc as a time base by using equations (4) and (8) to form:
We now have a table of the apparent fB frequencies versus a normalized temperature, T.
Therefore, a polynomial can be constructed which has the form:
T = A' + B'fn + C'fB2 + D'fB3 + ... (10)
where A', B', C', D', ... are the zeroth, first, second, third ... order frequency
coefficients of temperature.
This expression can then be substituted into equation (6) yielding an expression of the following form: bf = A + Bfn + CfB Dfn3 + ... (11)
Hence, by measuring the B-mode frequency signal using the C-mode signal as a frequency base, a correction factor polynomial valid over the entire calibration range can be generated. This correction factor can then be used with either of equations (3) and (4) to correct the measured value of the selected frequency signal, or to stabilize the C mode frequency signal by shifting its frequency as necessary, respectively.
To implement the curve-fitting technique, the coefficients of equation (10) or (11) are determined initially for the individual crystal or for a production class of crystals, and stored in the apparatus as fixed constants over the entire operational temperature range. In operation, fn which can be the B mode frequency or a selected first order function of both the B and C mode frequencies, e.g., the ratio or difference, is formed, measured, and applied to a processor wherein signals representative of the expressions of equation (10) or (11) are formed and added to form yet another signal that is representative of the crystal temperature or the desired correction factor.
In the look-up table technique, the value of the desired correction factor or of the temperature is initially stored in the look-up table with fn, the value of the B mode frequency or of a selected function of both the B and C mode frequencies, as a pointer at each selected temperature. In operation. fB is formed and measured to generate a pointer to the desired information in the look-up table. If the value of fB is the same as one of the pointers of the look-up table, the information stored at that location is transferred to a processor. The value of fB may be between two pointer values of the look-up table.When this occurs, the look-up table values associated with these adjacent pointers are transferred to the processor where an appropriate interpolation is performed to determine the value of the temperature or correction factor associated with this intermediate pointer.
The interpolation technique used when the value of the pointer is intermediate two other pointer values in many applications will be linear. This then requires that the initial measurements of the crystal frequencies be taken at selected temperatures which are sufficiently close together such that the desired correction factor or temperature curves as a function of fg between these temperature values are predominantly linear. If these curves are non-linear between the selected temperatures it then would be necessary to include polynomial coefficients in the look-up table for each pointer. These coefficients would then be used in any known interpolation polynomial to determine the correction factor for the intermediate pointer.
In Figures 2 to 4, the arrows which are shown, indicate the direction of forward power or information flow in each of the implementations.
Referring now to Figures 2a-d, there is shown a variety of implementations of an oscillator 11 wherein a doubly rotated TTC quartz crystal resonator 10 is vibrating in two thickness modes simultaneously. In Figure 2a there is shown a single quartz resonator 10 of the TTC type discussed above, disposed between electrodes 12 and vibrated simultaneously in its B and C modes by application of an A-C signal to electrodes 12 by an amplifier 13.
This amplifier has two inputs which it combines internally to excite both modes of vibration within the resonator 10 at different frequencies, with the frequencies of the amplifier 13 corresponding to the B and C mode frequencies of the crystal. Filter networks 18 and 20, each having appropriate poles and/or zeros relative to said frequencies, will separate the energy from the vibration in the two modes through the single pair of electrodes 12. In this configuration, the C and B mode frequency signals are provided for subsequent circuitry on the output ports of the filter networks 18 and 20, respectively.
In Figure 2b, the oscillator 11 is shown with the same configuration as in Figure 2a with amplifier 13 replaced by a negative resistance circuit 15. This negative resistance circuit 15, as does the amplifier 13, excites the two separate modes of vibration of the resonator 10.
Figure 2c shows a second implementation of the oscillator 11 using a negative resistance circuit 15. In this circuit configuration a negative resistance circuit 15 has been disconnected from the lower electrode 12 as shown in Figure 2b, and reconnected to the node between filter networks 18 and 20 and the upper electrode 12. Additionally, the lower electrode 12, the negative resistance circuit 15, and the filter networks 18 and 20 are all referenced to the same return bus. The oscillator 11 of Figure 2d shows a circuit configuration with amplifiers 14 and 16 each designed to excite a separate mode of vibration within resonator 10 with amplifiers 14 and 16 corresponding to the C and B mode frequencies, respectively. Also shown in Figure 2d are electrodes 12 and filter networks 18 and 20 which are included for the same purposes as discussed in relation to Figure 2a.In this configuration the C and B mode frequency signals are provided for subsequent circuitry from the amplifiers 14 and 16 respectively.
In Figure 3, there is shown a first embodiment of the invention with open loop temperature compensation. This implementation is used as a means for applying a correction factor to a measurement of the unknown frequency of an external signal where the C mode frequency provides the time base reference. The B and C mode frequency signals are applied to a mixer 22 from an oscillator 11. From these signals, the mixer 22 produces a difference frequency signal, fD which is then applied to a frequency measuring counter subsystem 24. The C mode frequency signal is also applied to the counter subsystem 24 as a time base reference. If this implementation is to be used to measure the frequency of a third signal, this third signal is also applied to the counter subsystem 24 from an external source 26 as indicated by a broken arrow 25.Using the C mode frequency signal as a reference signal, the apparent frequencies of the fD signal and the third signal are measured by the counter subsystem 24.
The counter subsystem 24 then converts both frequency measurements to electrical signals with a format that is compatible to subsequent circuit elements. These measurement signals are then transferred to a processor 28 either serially or in parallel. This transfer of the measurement signals may be made and transferred under the control of the processor 28 as indicated by a broken arrow 29.
The processor 28 can be implemented to apply either the curve fitting technique or the look-up table technique as discussed above with digital or analog circuits. Examples of these various implementations are:
Frequency measurement subsystems 24 and 38 - Hewlett-Packard Models 5300B,
5312A and 5308A
Digital curve fitting processor 28 - Hewlett-Packard Model 9825A
Analog curve fitting processor 28 - Operational amplifiers with non-linear function
generators composed of resistors. diodes and transistors
Digital look-up table processor 28 - Hewlett-Packard Model 9825A
Anaog look-up table processor 28 - Operational amplifiers and multiple threshold
circuits with resistive ladders
Rate multiplier 42 - Texas Instruments SN5497 In each of these implementations, the processor 28 utilizes the measurement signals to generate a signal that accurately represents the temperature of the resonator 10 and to generate a corrected measurement signal that accurately represents the actual frequency of the third signal. This accurately representative signal is then coupled to a display subsystem 30
which then communicates the desired temperature and frequency information to an operator and/or additional systems elements.
Figure 4 shows another embodiment of the present invention which also employs open loop temperature compensation. This implementation provides a stabilized frequency output signal that is derived from the C mode frequency signal from an oscillator 11. In addition to the oscillator 11 and mixer 22, this embodiment includes a frequency measuring subsystem 38, a subtractor 40, and a rate multiplier 42.
The mixer 22 receives the B and C mode frequency signals from the oscillator 11 from which it generates a difference frequency signal, fD. The difference frequency signal is then coupled to the frequency measuring subsystem 38. The frequency measuring subsystem 38 consists of conventional digital binary circuitry, analog frequency to voltage conversion circuitry, or a combination of analog-digital tachometric circuitry. This frequency measuring subsystem may require a reference frequency in which case the resultant measurement is the ratio between the reference frequency and the measured frequency.
Should a reference frequency signal input be utilized it could be the C mode frequency signal as indicated by a dashed line 39.
The frequency measuring subsystem 38 in turn generates a first electrical signal corresponding to the measured difference frequency, fD. The first electrical signal is then applied to the subtractor 40 where it is subtracted from a second signal that is representative of a B and C mode frequency difference where no correction to the C mode frequency is required.
The result of this subtraction produces a third electrical signal that is applied to a processor section of the subtractor 40 to generate a correction factor signal to provide the necessary frequency shift to the C mode frequency. This processor section of the subtractor 40 can be implemented and operates as does the processor 28 of the previous embodiment of Figure 3. The rate multiplier 42 receives two input signals, the correction factor signal at its rate input port and the C mode frequency signal at its clock input port. The resultant output signal from the rate multiplier 42 is a stabilized frequency output signal whose frequency is that of the clock signal, i.e., C mode frequency signal, shifted in response to the rate input signal, i.e., correction factor signal.
In each of the above oscillating circuits the nominal operating frequency may be made externally adjustable and/or controllable by the inclusion of mechanically andíor electrically variable components in the fashion of present art as seen in practically all crystal oscillators (e.g., VCXO controls). This same external control result can also be achieved by applying the controlling influence to any appropriate point in the compensation loop (e.g., a varactor to vary the phase shift in one resonant frequency path as a result of a feedback signal to maintain that frequency within selected tolerance limits).
WHAT WE CLAIM IS:
1. Signal generation apparatus comprising:
a quartz crystal resonator having a selected crystallographic orientation that is equal to
(yxwl) 21.93 /33.93 +2 for providing static and dynamic thermal transient compensation, and having first and second thickness modes of vibration in response to an electric field applied thereto, vibration in each of said modes being characterized by a selected frequency-temperature deviation characteristic;
means for generating and supplying said electric field to said quartz crystal resonator and for isolating the first and second frequency signals of said first and second modes of vibration, respectively; and
compensation means coupled to receive said first and second frequency signals for
generating an output signal that is relatively independent of any temperature induced
deviations of said first and second frequency signals, one of said first and second frequency
signals received by the compensation means being representative of the temperature of said
quartz crystal resonator and used to generate an intermediate signal used in the generation
of the output signal.
2. Signal generation apparatus as in claim 1 wherein:
said one of the first and second frequency signals and its corresponding thickness mode of
vibration comprises the B mode frequency signal and its B mode of vibration of the quartz
crystal resonator each having a predominantly linear frequency-temperature characteristic
over a selected temperature range; and
said other of the first and second frequency signals and its corresponding thickness mode
of vibration comprises the C mode frequency signal and its C mode of vibration of the
quartz crystal resonator each having a predominantly third order frequency-temperature
characteristic over a selected temperature range.
3. Signal generation apparatus as in claim 2 wherein said compensation means
comprises:
input means coupled to said electric field generating and supplying means for receiving at
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (17)
1. Signal generation apparatus comprising:
a quartz crystal resonator having a selected crystallographic orientation that is equal to
(yxwl) 21.93 /33.93 +2 for providing static and dynamic thermal transient compensation, and having first and second thickness modes of vibration in response to an electric field applied thereto, vibration in each of said modes being characterized by a selected frequency-temperature deviation characteristic;
means for generating and supplying said electric field to said quartz crystal resonator and for isolating the first and second frequency signals of said first and second modes of vibration, respectively; and
compensation means coupled to receive said first and second frequency signals for
generating an output signal that is relatively independent of any temperature induced
deviations of said first and second frequency signals, one of said first and second frequency
signals received by the compensation means being representative of the temperature of said
quartz crystal resonator and used to generate an intermediate signal used in the generation
of the output signal.
2. Signal generation apparatus as in claim 1 wherein:
said one of the first and second frequency signals and its corresponding thickness mode of
vibration comprises the B mode frequency signal and its B mode of vibration of the quartz
crystal resonator each having a predominantly linear frequency-temperature characteristic
over a selected temperature range; and
said other of the first and second frequency signals and its corresponding thickness mode
of vibration comprises the C mode frequency signal and its C mode of vibration of the
quartz crystal resonator each having a predominantly third order frequency-temperature
characteristic over a selected temperature range.
3. Signal generation apparatus as in claim 2 wherein said compensation means
comprises:
input means coupled to said electric field generating and supplying means for receiving at
least the B mode frequency signal of said B and C mode frequency signals and for providing a third signal whose frequency is representative of the internal temperature of the quartz crystal resonator;
counter means coupled to receive, and for counting the freqency of said third signal and generating a fourth signal with an encoded value that is representative of the counted frequency value of the third signal; and
processor means coupled to receive said fourth signal for producing therefrom a fifth signal with an encoded value that is a function of the temperature of the quartz crystal resonator, the fifth signal being said intermediate signal.
4. Signal generation apparatus as in claim 3 wherein said processor means produces the fifth signal by a curve fitting technique.
5. Signal generation apparatus as in claim 3 wherein said processor means produces the fifth signal by a look-up table and interpolation technique.
6. Signal generation apparatus as in claim 3 wherein:
said counter means is further coupled to receive an unknown frequency signal from an external signal source for counting the frequency of the unknown signal and for generating a sixth signal with an encoded value that is representative of the counted frequency value of the unknown signal, said C mode frequency signal also being coupled to the counter means to provide a time base reference signal for the counting of the frequency of both the third and the unknown frequency signals;
said fifth signal has an encoded value that is representative of a correction factor to the measured value of the frequency of the unknown signal using the temperature sensitive C mode frequency signal; and said processor means is further coupled to receive the sixth signal for algebraically combining the encoded values of the fifth and sixth signals to form a value to be encoded into the output signal, said encoded value of the output signal being representative of an accurate measure of the frequency of the unknown signal corrected for the temperature frequency deviation of the C mode frequency.
7. Signal generation apparatus as in claim 6 wherein said compensation means further includes display means coupled to receive the output signal for displaying its encoded value.
8. Signal generation apparatus as in claim 3 wherein: said processor means includes means for subtracting from the encoded value of the fourth signal a value that is representative of an encoded value of the fourth signal where the C mode frequency is within a selected accuracy of a preselected output signal frequency forming from the subtraction result a sixth signal, from the sixth signal the processor means generates the fifth signal, said fifth signal having an encoded value representative of a correction factor necessary to shift the C mode frequency to maintain the output signal within the selected accuracy; and
said compensation means further comprises rate multiplier means having clock and rate input ports, said clock and rate input ports being coupled to receive the C mode frequency signal and the fifth signal, respectively, and wherein an output signal is generated having a frequency that corresponds to the C mode frequency shifted in response to the fifth signal, said output signal having a frequency within the selected accuracy.
9. A method of generating a signal, said method comprising the steps of:
exciting a quartz crystal resonator having a selected crystallographic orientation that is equal to (yxwl) 21.93 /33.93 t2" for providing static and dynamic thermal transient compensation into simultaneous vibration in a first and second independent thickness mode of vibration, vibration in each of said modes being characterized by a selected frequency-temperature deviation characteristic;
isolating from each other a first and a second frequency signal corresponding to the first and the second mode of vibration respectively; and generating from said first and second frequency signals an output signal that is relatively independent of any temperature induced deviations of said first and second frequency signals, one of said first and second frequency signals utilized in the generation of the output signal being representative of the temperature of said quartz crystal resonator and used to generate an intermediate signal used in the generation of the output signal.
10. A method of generating a signal as in claim 9 wherein: said one of the first and second frequency signals and its corresponding thickness mode of vibration comprises the B mode frequency signal and its B mode of vibration of the quartz crystal resonator each having a predominantly linear frequency-temperature characteristic over a selected temperature range; and said other of the first and second frequency signals and its corresponding thickness mode of vibration comprises the C mode frequency signal and its C mode of vibration of the quartz crystal resonator each having a predominantly third order frequency-temperature characteristic over a selected temperature range.
11. A method of generating a signal as in claim 10 wherein the step of generating an output signal includes:
producing a third signal whose frequency is representative of the internal temperature of the quartz crystal resonator from at least one of the B and C mode frequency signals;
counting the frequency of the third signal and generating a fourth signal with an encoded value that is representative of the counted frequency value of the third signal; and
processing the fourth signal to produce a fifth signal with an encoded value that is a function of the temperature of the quartz crystal resonator, the fifth signal being said intermediate signal.
12. A method of generating a signal as in claim 11 wherein the step of processing the fourth signal includes:
predetermining and storing. coefficients of an nth order polynomial that is a function of the encoded value of the fourth signal to accurately produce the encoded value of the fifth signal over the entire selected temperature range; and
algebraically combining the encoded value of the fourth signal with the stored coefficients of the nth order polynomial to form the encoded value of the fifth signal.
13. A method of generating a signal as in claim 11 wherein the step of processing the fourth signal includes:
predetermining the values to be encoded in each of the fourth and fifth signals with the quartz crystal resonator operating at a plurality of selected temperatures;
prestoring the individual predetermined values to be encoded in the fifth signal in a storage device with the corresponding predetermined values of the fourth signal as pointers thereto;
applying the actual encode value of the fourth signal to the storage device;
identifying a plurality of pointers having values between which the actual encoded value of the fourth signal falls; and
interpolating between the stored values to be encoded into the fifth signal corresponding to said plurality of pointers utilizing the plurality of pointers and the actual value encoded in the fourth signal;
said plurality of pointers being a single pointer when there is agreement between the actual encoded value of the fourth signal and one of the stored pointers wherein the value to be encoded in the fifth signal is the stored value corresponding to said single pointer.
14. A method of generating a signal as in claim 11 wherein the step of generating an output signal further includes the steps of:
utilizing the C mode frequency signal as a time base reference for counting the frequency of other signals:
counting the frequency of an externally applied unknown frequency signal and generating a sixth signal with an encoded value that is representative of the counted frequency value of the unknown frequency signal using the temperature sensitive C mode frequency signal; and
algebraically combining the encoded values of the fifth and sixth signals forming a value to be encoded into the output signal, the encoded value of the output signal being representative of an accurate measure of the frequency of unknown signal, the encoded value of said fifth signal being a correction factor to the encoded value of the sixth signal.
15. A method of generating a signal as in claim 11 wherein:
the step of processing the fourth signal includes the steps of:
subtracting from the encoded value of the fourth signal a value that is representative of an encoded value of the fourth signal where the C mode frequency is within a selected accuracy of a preselected frequency to form a sixth signal having an encoded value equivalent to the result of the subtraction;
converting the encoded value of the sixth signal into a value representative of a correction factor necessary to shift the C mode frequency to maintain this frequency within the selected accuracy of the preselected frequency; and
encoding the C mode frequency correction factor value into the fifth signal; and
the step of generating an output signal further includes the step of shifting the frequency of the C mode signal in response to the fifth signal to produce the output signal having the preselected frequency within the selected accuracy.
16. Signal generation apparatus substantially as herein before described with reference to the accompanying drawings.
17. A method of generating a signal substantially as herein described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4906277A GB1596845A (en) | 1977-11-25 | 1977-11-25 | Quartz crystal resonator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4906277A GB1596845A (en) | 1977-11-25 | 1977-11-25 | Quartz crystal resonator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1596845A true GB1596845A (en) | 1981-09-03 |
Family
ID=10450987
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB4906277A Expired GB1596845A (en) | 1977-11-25 | 1977-11-25 | Quartz crystal resonator |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB1596845A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110311673A (en) * | 2019-06-24 | 2019-10-08 | Oppo广东移动通信有限公司 | A kind of transmitting frequency calibration method, terminal and storage medium |
-
1977
- 1977-11-25 GB GB4906277A patent/GB1596845A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110311673A (en) * | 2019-06-24 | 2019-10-08 | Oppo广东移动通信有限公司 | A kind of transmitting frequency calibration method, terminal and storage medium |
| CN110311673B (en) * | 2019-06-24 | 2024-02-02 | Oppo广东移动通信有限公司 | Frequency calibration method, terminal and storage medium |
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| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19931125 |