SU1615645A1 - Transducer of resistance of quartz resonator - Google Patents

Abstract

The invention relates to a measuring technique and can be used as a measuring transducer of the active resistance of a quartz resonator at a frequency of its series resonance in a time interval. The purpose of the invention is to improve the accuracy of the conversion. By introducing the comparator 6, element 7, the reference voltage source 9 and the control voltage generator 10, the active resistance of the crystal oscillator 3 is converted by recording the moment of occurrence or failure of oscillations of the oscillator 1, resulting in instability of the amplitude of the oscillations generated does not affect the accuracy of the conversion . In addition, the execution of the oscillator 1 in the form of a wideband amplifier 2 with positive feedback, the negative crystal feedback circuit of which includes the quartz resonator under study, eliminates the error associated with the uncertainty of the phase shift in the amplifier when using quartz resonators with different resonant frequencies. The converter also contains an amplifier 4, an amplitude detector 5, a voltage-controlled resistor 8, a time-domain converter to digital code 11. 4 Il.

Description

The invention relates to a gauge- and -th gauge and can be used as a measuring transducer of the active resistance of the quartz crystal HSTupa at the frequency of its series resonator in the time interval.

The aim of the invention is to improve the accuracy of the conversion,

FIG. 1 shows a functional diagram of the converter; FIG. 2 is an oscillator circuit; in fig. 3 variable resistor circuit; in fig. 4 shows timing diagrams explaining the operation of the converter;

The converter contains a controlled auto-oscillator 1, consisting of a first amplifier 2 with positive feedback and a quartz resonator 3 under investigation, a second amplifier 4, an amplitude detector 5, a comparator 6, an And 7 element, a voltage-controlled resistor 8, a constant source 9 reference voltage, control voltage generator 10, time interval transformer 11 in a digital code. The output of the oscillator 1 is connected through a series of second amplifier 4 and an amplitude detector 5 connected to the first input of the comparator 6, the BIU input of which is connected to the source E of the reference voltage. Between the output of the positive feedback circuit of aatogeopopop 1 vi common bus is connected a voltage controlled variable resistor 8, the control input of which is connected to the first output of the generator 10 of the control voltage, the second output of which is connected to the first input of the element 7 , the second input of which is connected to the output of the comparator 6, and the output to the input of the time interval is digital code 11,

The first positive feedback amplifier 2 contains a resistor 12 connected by a single output to a resistor 13, a potentiometer 14, a resistor 15 and a capacitor 16, a diode 17, a cathode connected to the base of transistor 18. whose collector is connected to one output of resistor 19, the base transistor 20 is connected through a capacitor 21 to a capacitor 22, the emitter of transistor 20 is connected to the collector of transistor 23, the base of which through diodes 24 and 25 is connected to a common bus, the emitter of transistor 23 is connected to a common bus through a resistor 26 one of the terminals of the resistor 27, the other terminal of which is connected to the common point of the capacitors 21 and 22 and resistor 3 19,

As a voltage-controlled resistor 8, a field-effect transistor (FIG. 3) can be used, the terminals of the resistor being the outputs of the source and drain, the control input being the output of the gate of the field-effect transistor. In order to select the required voltage shape in series with the gate and between the gate and drain, resistors may be included.

The device works as follows.

A wideband amplifier 2 with positive feedback (PIC) is a potentially self-oscillating system that itself is excited when the known amplitude balance condition is fulfilled.

Iki 1 (1)

on one of the frequencies lying in the passband of the wideband amplifier 2 with PIC, In condition (1) through | К | denotes the module of the complex loaded gain factor of amplifier 2; in I / SI, the module of the complex loaded

transmission circuit feedback ratio,

In amplifier 2 (FIG. 2), the POS circuit is formed by a coupling capacitor 21, the value of which is chosen so large that I / S 1 can be considered in the entire operating frequency band of the device. Therefore, fulfillment or non-fulfillment of condition (1) is achieved by adjusting only the loaded gain factor K

 I; I, the value of which varies within О К К max depending on the resistance value Re of the controlled resistor 8 connected through the high-capacity coupling capacitor 22

parallel to the resistance of the collector load of the transistor 18 broadband amplifier 2 with PIC,

In addition to the value of Re controlled resistor 8, the gain K depends

also on the magnitude Gh of the active equivalent resistance of the quartz resonator 3 at the series resonator.

In this case, in the device between K, Re and Gx, the following qualitative relations are fulfilled:

the more Re, the more K; the more Gh, the less K, the Controlled resistor 8 and the wideband amplifier 2 with the PIC are built so

that when Re Re, the value of K is such that condition (1) is fulfilled with a margin at Gx, G, max, that is, for the worst case. Then, when RS increases from Yazmin to Rvmax, for example, according to the linear law Re RSMMH + at, at a given value of Gx1, self-oscillations occur in auto-oscillator 1 at such a time ti, at which strict equality

  1 .. (2)

A similar pattern is observed when Re decreases from Pvmax to RSMHH, i.e. with the breakdown of self-oscillations. If instead of a given quartz resonator having a series resonance frequency (very close to self-oscillation frequency) resistance Gx1, another measured quartz resonator is connected with the same frequency of the series resonator and the corresponding resistance Gx2, for example, greater than Gx1, then since this decreases, the excitation of self-oscillations now occurs at time 12. At the same time, t2 ti.

Thus, the device converts to a time interval.

At some point in time, determined, for example, by applying a start pulse to the input of the control voltage generator 10, the latter produces a gate pulse (Fig. 4a) and a linearly varying voltage (Fig. 46), which controls the resistance of the resistor 8. At the moment when the gain in the feedback loop reaches the value (Ki-LySl 1, an alternating voltage occurs at the output of the oscillator (Fig. 4c). During the reverse control voltage, if the balance condition is violated, the amplitude of the 35 ci stops. After output detection voltage of the autogenerator, the video pulse from the output of the amplitude detector 5 (Fig. 4c) is fed to the first input of the comparator b, where it is compared with a certain reference voltage, at the output of the comparator 6 a pulse is generated, the front edge of which is delayed relative to the peaking front of the strobe pulse time ti, which is proportional to the measured resistance Gh. At the output of element I 7, a pulse is formed, the duration of which, for a known strobe pulse duration, is also linearly related to the measured value of Gh.

20

25

thirty

50

 . 35 40 45

ten

15

20

25

thirty

0

It can be obtained experimentally.

The reverse voltage of the control voltage can also be used to measure rh (Fig. 4e). In this case, the leading edge of the strobe pulse must be delayed by tc.

Amplifier 4 is used to sharpen the video pulse at the output of the Detector (Fig. 4d), which helps reduce the conversion error due to the finite rise time and the breakdown of oscillations of the autogenerator. The time interval into digital code converter 11 makes it possible to present the converted resistance Gx in a more convenient for measurement form. In addition, it is often not necessary to measure the absolute value of the Gh, and it is important to know only its deviation from a certain specified value or from the value measured in previous experience (for example, when using a quartz resonator as a sensor of some physical parameter). In this case, the previous code value corresponding to the previously converted GHT value is stored in the memory of the converter 11. During the second conversion cycle, the output of the converter 11 generates a code corresponding to the difference gx2 - Gx1, where Gx2 is the active resistance value of the quartz resonator in the second experiment.

Due to the fact that for the conversion of Gx only the registration of the moment of occurrence or generation failure is used, the instability of the amplitude of the generated oscillations does not introduce an error in the result of the transformation.

The implementation of a controlled autogenerator in the form of an amplifier covered by a positive feedback, the negative crystal feedback circuit of which includes the quartz resonator under study, makes it possible to use a broadband amplifier in it, as a result of which the error associated with the phase shift uncertainty is eliminated. in the amplifier when measuring Gh quartz resonators with different resonant frequencies.

tBbix tc - ti b (Ro - Gh), (3)

where b and RO are the parameters determined experimentally.

In general, the R8 (Uynp) relationship may be non-linear. In this case, the dependence tsbix f (rx) is also non-linear, however

five

Claims (2)

Claim 1. Intensity converter of a quartz resonator, containing a controlled oscillator, the output of which is connected to an amplitude detector, and a control input - with the first output of the controlled resistor, the second output of which is connected to the common bus so that in order to increase : conversion accuracy, a comparator, a reference voltage source, an AND element and a control voltage generator, the first output of which is connected to the control input of the controlled resistor, are entered into it, the second output is connected to the first input of the AND element, the second input of which is connected to the output the comparator, and the output is the converter output, with the first input of the comparator connected to the output of the amplitude detector, and the second input to the source of the reference voltage. 2. The converter according to claim 1, wherein the controlled oscillator comprises an amplifier, made in the form of two series-connected amplifier stages, a positive feedback circuit connected between the first output of the second stage and the input of the first cascade, and the quartz resonator under investigation, with the first amplifying the cascade contains a transistor, the emitter of which is connected in parallel with a current regulator and the quartz resonator under investigation connected to a common bus, the collector is connected to the input of the second stage, and also via a load resistor to the power supply, and the base is connected to the bias circuit and the output of the positive feedback circuit , with the first output of the second stage being the control input of the oscillator, and the second output of the second cascade - with the output of the oscillator.