RU2007839C1 - Device for thermal correction of crystal oscillator - Google Patents

Abstract

FIELD: electric engineering. SUBSTANCE: device has crystal oscillator 1 having positive thermal effect on generated frequency, crystal oscillator 2 having negative thermal effect on generated frequency, frequency difference detector 3, frequency divider 4, first counter 5, second counter 6, first RS flip-flop 7, matching gate 8, third counter 9, digital comparator 10, NAND gate 11, second RS-flip-flop 12, OR gate 13. Frequency difference detector 3 detects difference between frequencies of crystal oscillators 1 and 2. This difference is converted by frequency divider 4 into number of pulses which is stored in counter 5. Then by means of first and second RS-flip-flops 7, 12, third counter 9 and digital comparator 10 this number is added to number of pulses running through second counter 6. This results in generation of standard time duration that corresponds to standard frequency. EFFECT: increased speed and increased precision of thermal correction. 2 dwg

Description

 The invention relates to thermal compensation devices for reference crystal oscillators and other highly stable generators. It can be used to create master oscillators of small-sized portable equipment, which is subject to increased requirements for temperature stabilization of the frequency, limiting weight and power consumption.

 Known thermally compensated reference quartz oscillator containing a series-connected temperature sensor, a modulator, to the second input of which is connected a function generator, an analog-to-digital converter, a storage unit, a digital-to-analog converter, a low-pass filter, a control element and a controlled generator, where the frequency of the controlled generator is adjusted in depending on the temperature value.

 The disadvantage of this device is the well-known inertia of temperature sensors and a complex conversion process that introduces an additional error.

 It is also known a device adopted as a prototype, comprising a series-connected reference quartz oscillator and a frequency subtractor, a heat-sensitive oscillator, a constant memory unit, integrating link and a controlled oscillator connected in series, the output of which is connected to the second input of the frequency subtractor, a frequency divider, the first and second keys, first and second storage registers, DAC, synchronization unit, reversible counter [1].

 The disadvantages of the device are a complex and divisive conversion process and low accuracy caused by the use of analog elements.

 The aim of the invention is to increase the speed and accuracy of thermal compensation, which is ensured by the exclusion from the composition of the generator of the temperature control system and its elements, which are inertial; immediate availability for use; exception from the frequency correction system of the generator of analog elements, introducing additional errors.

 The goal is achieved by the fact that in the temperature compensation device of the crystal oscillator containing a crystal oscillator with a positive temperature coefficient of frequency, a crystal oscillator with a negative temperature coefficient of frequency, a frequency divider, a frequency difference shaper and a first counter, while the outputs of a crystal oscillator with a positive temperature coefficient of frequency and crystal generators with a negative temperature coefficient of frequency are connected to the corresponding inputs of the frequency difference former from, a second counter, a first RS-trigger, is connected in series; a coincidence element, a third counter, a digital comparator, an AND-NOT element and a second RS-trigger, and an OR element is inserted between the non-inverse output of the second RS-trigger and the S-input of the first RS-trigger, while the frequency divider is connected between the output of the frequency difference driver and the counter input of the first counter, the zero input of which is connected to the zero input of the third counter and connected to the inverse output of the second RS trigger, the counter input of the second counter is connected to the second input of the matching element and connected to the output of quartz g generator with a positive temperature coefficient of frequency; the second input of the AND-NOT element is connected to the first input of the coincidence element, the S-input of the second RS-trigger is connected to the S-input of the first RS-trigger, the information outputs of the first counter are connected to the corresponding inputs of the digital comparator, and the input "START" and the output of the thermal compensation device crystal oscillator are respectively the other input of the OR element and non-inverse output of the second RS-trigger.

 Comparative analysis with the prototype shows that the claimed device is characterized by the presence of new elements and functional relationships, which meets the criterion of "novelty."

 Comparison of the claimed device for thermal compensation of a crystal oscillator with other technical solutions shows that the frequency divider, second and third counters, matching circuit, first and second RS-flip-flops, NAND element, digital comparator and OR element are known, but combining them with new functional connections gives the ability to increase the accuracy (or stability) of the frequency of the crystal oscillator without measuring and maintaining a constant temperature in the zone of the crystal, while providing immediate readiness for use eniyu and intermediate analog conversion are eliminated. Thus, the proposed thermal compensation device of a quartz generator has new properties, such as high speed and accuracy, which meets the criterion of "significant differences".

 In FIG. 1 is a functional diagram of a thermal compensation device of a crystal oscillator; in FIG. 2 is a timing diagram explaining the operation of the device.

 The temperature compensation device of a crystal oscillator contains a crystal oscillator 1 with a positive temperature coefficient of frequency (TFC), a crystal oscillator 2 with a negative TFC, a frequency difference shaper 3, a frequency divider 4, a first counter 5, a second counter 6, a first RS flip-flop 7, a coincidence element 8 , the third counter 9, the digital comparator 10, the element AND-NOT 11, the second RS-trigger 12, the element OR 13.

 The outputs of the quartz oscillator 1 with positive TFC and the quartz generator 2 with negative TFC are connected to the corresponding input of the frequency difference driver 3, the output of which is connected to the input of the frequency divider 4, the output of the frequency divider 4 is connected to the information input of the first counter 5, the second counter 6 is connected in series, the first RS-flip-flop 7, the coincidence element 8, the third counter 9, the digital comparator 10, the AND-NOT element 11 and the second RS-flip-flop 12, between the inverse output of which and the S-input of the first RS-flip-flop 7 the element OR 13 is inserted, when this, the zero input of the first counter 5 is connected to the zero input of the third counter 9 and is connected to the inverse output of the second RS-trigger 12, the counting input of the second counter is connected to the second input of the coincidence element 8 and connected to the output of the crystal oscillator 1 with a positive TFC, the second input of the AND-NOT element is connected to the first input of the coincidence element 8, the S-input of the second RS-trigger 12 is connected to the S-input of the first RS-trigger 7, the information outputs of the first counter 5 are connected to the corresponding inputs of the digital comparator 10, input th "START" and the output of the temperature compensation crystal oscillator are respectively the other input of the OR gate and the non-inverting output of the second RS-flip-flop 12.

 The second counter 6 has an overflow output that is connected to the input R of the first RS flip-flop. A quartz oscillator 1 with a positive TFC and a quartz oscillator 2 with a negative TFC must provide pulsed signals and be in the same volume (quartz resonators in close proximity). TFCs of quartz resonators are selected with a linear dependence [4]. The remaining elements are well known.

The device operates as follows. A quartz oscillator 1 with a positive TFC and a quartz oscillator 2 with a negative TFC are adjusted at a lower value of the operating temperature range of the thermal compensation device of the quartz oscillator so that the frequencies of the oscillators are equal to each other and, accordingly, the reference frequency F _about . At this frequency, a reference time interval t _o = N _o T _o is formed at the output of the device. where N _o is the number of pulses passing through the second counter 6 until an overflow pulse appears at its output (i.e., N _o is the capacity of the second counter 6); T _o = 1 / F _o - the repetition period of the pulses of the reference frequency.

 The process of forming a model interval is as follows. In the initial state, the first 5, second 6, and third 9 counters are reset to zero by the potential of the logical unit taken from the inverse outputs of the first 7 and second 12 RS-flip-flops, which are in the initial state. At the first input of the OR element, a logic zero signal, at the second logical unit. To start the device to the second input of the OR circuit (Input "START"), it is necessary to apply a low potential corresponding to a logical zero for the entire time of operation. Then the first 7 and second 12 RS-flip-flops will go into a single state and with zero potentials from the inverse outputs enable the counting of pulses by the first 5 and third 9 counters and at the same time the passage of the pulse sequence through the matching circuit and the AND-NOT 11 element is prohibited.

 The second counter 6 starts the pulse count from the quartz oscillator 1 with a positive TFC. When the second counter 6 is full, a zero level pulse from the overflow output will transfer the first RS-trigger 7 to zero, which will reset the second counter 6 to zero (with a count prohibition) and to the corresponding inputs of the matching circuit 8 and the AND-NOT element with a logic one 11 will enter a logical unit and open them.

 If the frequencies of the crystal oscillators 1 and 2 are equal, then there will be no pulses from the frequency difference shaper 3 through the divider 4 to the first counter 5, a zero code will be present on its information outputs, therefore, at the moment the first RS-trigger goes to zero, when on the information the outputs of the third counter 9 are a zero code, the digital comparator 10 will work and give a signal (about the equality of codes) through an open AND-NOT element to translate the second RS-trigger 12 to the zero state, which gives out signals: from a non-inverting output to the end ii exemplary time slot and the start of the device, ie, the formation of the following exemplary slot (assuming the presence of the output "START" logical zero)..; from the inverse output will reset the first 5 and second 9 counters to zero.

With increasing temperature, the frequency f _{1 of the} crystal oscillator 1 with a positive TFC increases, and the repetition period decreases accordingly from T _about to T ₁ , then
t _o = N _o T ₁ + n ₁ T ₁ = (N _o + n ₁ ) T ₁ ,
where n ₁ is the number of periods T ₁ that must be added in order to obtain a reference time interval t _o . The frequency f _{2 of the} crystal oscillator 2 with a negative TFC decreases, i.e.

f ₁ = F _o + α ₁ t ^o F _o = F _o (1 + α ₁ t ^o ),
f ₂ = F _o + (- α ₁ t ^o F _o ) = F _o (1 - α ₂ t ^o ) where α ₁ and α ₂ are the temperature coefficients of the frequency of the first 1 and 2 of the second crystal oscillators, t ^o is the temperature change in degrees C ^about .

=

, тогда
t₀= (N₀+n₁)T₁=

, откуда
N_o + n₁ = t_oF_o(1 + α ₁t^o) = N_oT_oF_o( 1 + +α₁t^o) = N_o (1 + α₁t^o), n₁ = α₁t^oN_o. Чтобы получить n₁ = α₁t^oN_o, необходимо с помощью формирователя разности частот 3 выделить разность частот
f₁ - f₂ = F_o + α₁t^oF_o - F_o + α₂t^oF_o = = ( α₁ + α₂)t^oF_o и поделить полученную разность делителем частоты 4 на коэффициент деления К, равный K=

, где α₁ и α₂ числовые значения ТКЧ без учета знака.

=

= α₁t^°F₀ А так как частота - это есть количество колебаний (в данном случае периодов импульсов) в единицу времени, то на выходе делителя частоты 4 получается число n₁ = α₁t^oN_o. которое подсчитывается первым счетчиком 5 и преобразуется в код, который подается на соответствующие входы цифрового компаратора 10.The pulse repetition period T _{1 of the} crystal oscillator 1 with a positive TFC will be equal to
T ₁ =

=

then
t ₀ = (N ₀ + n ₁ ) T ₁ =

from where
N _o + n ₁ = t _o F _o (1 + α ₁ t ^o ) = N _o T _o F _o (1 + + α ₁ t ^o ) = N _o (1 + α ₁ t ^o ), n ₁ = α ₁ t ^o N _o . In order to get n ₁ = α ₁ t ^o N _o , it is necessary to select the frequency difference using the frequency difference shaper 3
f ₁ - f ₂ = F _o + α ₁ t ^o F _o - F _o + α ₂ t ^o F _o = = (α ₁ + α ₂ ) t ^o F _o and divide the resulting difference by the frequency divider 4 by the division factor K, equal to K =

, where α ₁ and α _{2 are} numerical values of TFC without sign.

=

= α ₁ t ^° F ₀ And since the frequency is the number of oscillations (in this case, the pulse periods) per unit time, the number n ₁ = α ₁ t ^o N _{o is} obtained at the output of the frequency divider 4. which is counted by the first counter 5 and converted into a code that is fed to the corresponding inputs of the digital comparator 10.

In the case of the departure of the frequencies of the crystal oscillators 1 and 2, the process of forming a model time interval t _o occurs as follows. The launch of the device and the beginning of work on the formation of a model interval has been described previously.

When the second counter 6 is filled, a zero-level pulse from the overflow output transfers the first RS-trigger 7 to the zero position, which will “reset” the second counter 6 and disable the count, and open the match circuit 8 and the And NOT 11. The third counter 9 through an open matching circuit 8 will receive pulses from the output of the crystal oscillator 1 with a positive TFC, a code will be generated at the information outputs of the third counter 9. And when the number of pulses passing through the third counter 9 is equal to n ₁ = α ₁ t ^o N _o , that is, the codes from the information outputs of the first 5 and third 9 counters will be equal (the code at the outputs of the third counter 9 as if “catches up "the code at the outputs of the first counter 5), the digital comparator 10 will work and the output signal from the open element AND will NOT translate the second RS-trigger 12 to the zero state, which will give a low-level pulse from the non-inverse output about the end of the model time interval t _o and to starting the device, i.e., to form the next interval (provided that there is a logical zero at the "START" input), and the first and second counters will be reset to zero from the inverse output with a high-level pulse. The pulse duration will be determined by the delay on the response of the OR element and the second RS-trigger 12.

 Thus, the proposed device for thermal stabilization of a quartz generator in comparison with the prototype and analogues has higher speed and accuracy according to the following criteria: the proposed device does not have a temperature measurement operation as an inertial operation, regardless of the type of temperature sensor; in the proposed device there are no intermediate digital-to-analog and analog-to-digital conversions that reduce the accuracy of the prototype and analogue due to its own error. (56) Copyright certificate of the USSR N 1443120, cl. H 03, B 5/32, 1987.

Claims (1)

 A TEMPERATURE COMPENSATION DEVICE FOR A QUARTZ GENERATOR, comprising a quartz oscillator with a positive temperature coefficient of frequency, a quartz oscillator with a negative temperature coefficient of frequency, a frequency divider, a frequency difference generator and a first counter, wherein the outputs of a quartz oscillator with a positive temperature coefficient of frequency and a quartz oscillator with a negative temperature coefficient connected to the corresponding inputs of the shaper of the frequency difference, characterized in that, with In order to improve the speed and accuracy of thermal compensation, a second counter, a first RS-trigger, a coincidence element, a third counter, a digital comparator, an AND element - NOT and a second RS-trigger are introduced in series, and between the non-inverse output of the second RS-trigger and the S-input of the first An OR element is inserted into the RS-trigger, while the frequency divider is connected between the output of the frequency difference driver and the counting input of the first counter, the zero input of which is connected to the zero input of the third counter and connected to the inverse ode of the second RS-trigger, the counting input of the second counter is connected to the second input of the coincidence element and connected to the output of the crystal oscillator with a positive temperature coefficient of frequency, the second input of the AND element is NOT connected to the first input of the coincidence element, the S-input of the second RS-trigger is connected to S-input of the first RS-flip-flop, the information outputs of the first counter are connected to the corresponding inputs of the digital comparator, and the input "START" and the output of the thermal compensation device of the crystal oscillator are respectively different input of the OR element and the non-inverting output of the second RS-trigger.

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