CS201628B1 - Connection of the piezzoolectric crystal unit circuit - Google Patents

Description

The invention relates to a circuit of a piezoelectric crystal unit in which a series capacitance and a series inductance are connected to the piezoelectric crystal unit, and the series arrangement of the piezoelectric crystal unit and the capacitance is bridged by parallel capacitance.

So far, minimization has been achieved mainly by selecting crystal cuts of the required cutting angle orientation, for example for quartz cut AT resonators with an accuracy of + 30 to achieve a deviation of + 5. 10 “ ⁶ in the temperature range - 25 to -j- 65 ° C. Furthermore, temperature compensation of the frequency is utilized by means of a temperature-varying voltage, obtained by a resistor network of thermistors, supplied to the voltage-dependent capacity of the variocap connected in series with the piezoelectric crystal unit.

The disadvantages of the prior art are that it is very difficult to produce precise cutting angles. The selection of resonators with a cut accuracy of + 30 has a yield for frequency deviation of + 5.10 ^-6 around 30%; orientation with an accuracy of + 10 required to achieve a minimum possible deviation of + 2.5. 10 ' ⁶ in the range of -25 to -65 ° C, practically impossible to produce.

In the case of temperature compensation of the frequency using varikap, very small changes can be achieved, up to + 5. However, the design and implementation of a relatively complex circuit savings201628 are very demanding, the circuit requires the creation of a very stable variapro preload and the construction of the entire oscillator is subject to costly investment equipment.

The above drawbacks are overcome by the connection of a piezoelectric crystal unit in which the serial capacitance and series inductance are connected to the piezoelectric crystal unit and the series arrangement of the piezoelectric crystal unit and the capacitance is bridged by the parallel capacitance of the invention. 6 to 150 pF, parallel capacitance ranging from 0 to 100 pF, and series inductance ranging from 0.05 μΗ to 100 μΗ, where series capacitance and parallel capacitance and series inductance at room temperature satisfy the relation:

C ¹² (1 _{) 2}

C ₂ + C

Cikj

C |. + C ₂ + (cr + c5 ^ ia and serial capacity and parallel capacity satisfy the relation:

where k i, k being the temperature coefficients of capacitance, and i and a is the first order temperature coefficient of the cubic parabola of the temperature dependence of the piezoelectric crystal unit PKJ, respectively. m is the ratio of the dynamic capacity C _h and the static capacity G _{o of the} piezoelectric crystal unit PKJ.

The advantage of the circuit of the piezoelectric crystal unit according to the invention is that it achieves the desired frequency of the unit depending on the magnitude of the capacitance temperature coefficients without having to change the orientation of the quartz wafer plate. This means that it is not necessary to select crystal cuts with an accuracy of 30 arc seconds to achieve the optimum desired frequency response in the temperature range, but to adjust by selecting the appropriate C | resp C ₂ .

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be explained in more detail with reference to the accompanying drawing, in which Fig. 1 shows the circuit diagram of the piezoelectric crystal unit of the invention and Fig. 2 shows the temperature dependency of the quartz resonator frequency AT.

Typically, the circuit according to the invention is realized by a capacitance C1 connected in series with a piezoelectric crystal unit PKJ, a capacitance C ₂ which bridges in parallel a series combination of capacitance and piezoelectric crystal unit PKJ and an inductance L connected in series to this combination.

Temperature dependence of frequency of quartz resonators sectional AT is given by the cubic parabola as curve a in FIG. 2 type f-fo _ fo = i (T - T _o) + A ₂ (T - T _o) ² + a3 (T - To) ³ where f is the frequency of the piezoelectric crystal unit PKJ at temperature T; a1 and a2, a3 are first, second and third order temperature coefficients; f ₀ is the frequency at temperature T _o .

The invention is based on the possibility of adjusting the coefficient and the ₄ linear part of the aforementioned third dependence, the change of which can be used to rotate the cubic dish around its inflection point corresponding to the optimum cutting angle of the quartz plate of the resonator.

When using capacitances with linear temperature dependence with positive temperature coefficient of capacitance, the dish is rotated clockwise, see curve b of Fig. 2, with capacitances with negative coefficient in the tanned direction, curve c. Because the capacitance is connected to piezoelectric crystal It also causes the withdrawal of the frequency to higher values and a disadvantageous phase rotation.

The values of capacitances and inductances to achieve the required frequency deviations in the temperature range (most often to minimize them) are given by the first two relationships.

An exemplary embodiment of the circuit of a piezoelectric crystal unit according to the invention:

The piezoelectric crystal unit PKJ of the frequency f = 14.2 MHz, with a static capacitance C _o - 3.95 pF and a dynamic capacitance C _h = 16.8 mpF has a deviation A f / f = -j- 2.8. 10 ^-5 in the temperature range of -25 to -65 ° C. The course of the temperature dependence is given by the cubic dish with the value of the coefficient ai = —7,6.10 “ ⁷ . The compensation circuit consists of a capacitance Q = 37 pF connected in series with a piezoelectric crystal unit PKJ, a capacitance C ₂ = 27 pF connected in parallel to a combination of a serial capacitance Ci and a piezoelectric crystal unit PKJ, and a series inductance L = 2.1 μΗ. Capacitors C and C ₂ with a negative capacity temperature coefficient ki - k ₂ = —500. 10 ^{6 6} / ° C causes the rotation of the cubic parabola of temperature dependence so that the total frequency deviation in the temperature range is + 2.5.

. 10 “ ⁶ . This dish has a coefficient value of a '= -1.6. 10 "'. By using capacitance reactants with linear dependence of capacity on temperature (with constant temperature coefficient of capacitance in the temperature range), it is possible to achieve maximum temperature change of frequency given by optimal orientation of crystal cut. To achieve a smaller temperature change, it is necessary to use reactances with a non-linear capacity curve approaching the desired temperature range of the cubic dish with an inflection point around the temperature T _o . This way can obtain flatter frequency resulting cubic dependence of the third relationship when it changes the coefficient of the third order and _third

Claims (2)

OBJECT OF THE INVENTION A piezoelectric crystal unit wiring in which the serial capacitance and series inductance is coupled to the piezoelectric crystal unit and the series configuration of the piezoelectric crystal unit and capacitance is bridged by parallel capacitance, characterized in that the serial capacitance (Ci) is in the range of 6 to 150 pF, the parallel capacitance (C ₂ ) has a value in the range of 0 to 100 pF and the series inductance (L) has a value in the range of 0.05 μ přičemž to 100 μ přičemž, with the serial capacitance (Ci) and the parallel capacitance (C ₂ ) and (L) at room temperature satisfy the relation: C _o 2C | C k ^ ₂ CJ (1 c _{2 2} | ^{C | k |} c, C ₂ C, + C ₂ CjCJC ^! + Cik ₂ ) ·, v 2 + —δΓ + ο5 »-Γ ** and serial capacity (CJ and parallel capacity (C ₂ ) satisfy the relation: 1 - ω ² L (C _t + C ₂ ) = 0, where · kj, k ₂ are temperature coefficients of capacitance, aj resp. and \ is the first order temperature coefficient of the cubic parabola of the temperature dependence of the piezoelectric crystal unit PKJ, respectively. The temperature dependence of the parabola required by am is the ratio of the dynamic capacity C _h and the static capacity C _{o of the} piezoelectric crystal unit PKJ.