DE1591261B1 - Temperature compensated crystal piezoelectric circuitry - Google Patents

Description

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The invention relates to a temperature-compensated starting from the mentioned known crystal

piezo-electric crystal switching arrangement. circuit arrangement with more than one crystal, of

The aim of the invention is to create a ver which each lies in a circle, the circles

improved frequency-determining multiple crystal are connected in parallel with each other, according to circuit arrangement in which the modification of the 5 of the invention the crystals an at least approximated

Frequency with temperature is relatively small and very parabolic frequency-temperature characteristic with

small with respect to the frequency-temperature-characters-similar course and occur with the

ristic is that one of the crystals in the array has their individual reversal temperatures at im

would indicate if used alone. essentially the same frequency, but with different

Certain forms of crystals, in particular io different temperatures, which are in the distance from crystals with AT-section, show only relatively each other in a temperature line to be covered Frequency changes lie over a wide temperature range.

range. Such crystals, however, have the essentials of the preferred and simplest embodiment Disadvantage that the law of the frequency form of the invention are two circles in parallel temperature relationship very complex and provided in the 15 circuit, one of which is one Manufacture cannot be determined or calculated in advance- contains crystal and the other a second crystal is cash. This means that in many cases where it contains which is in series with a reactance like this a crystal is designed for a particular oscillator required that the second crystal is its reversal, he selected from a set or batch temperature at the same frequency as that of the first, must become. However, if a compensation circuit has to 20 at a different temperature. Compensating for temperature changes of frequency The invention is not limited to use used for such a crystal is that of only two crystals in parallel circles or Computation and interpretation complicated and difficult. -circuits limited; there were already one

However, there are crystal forms in which the law has larger numbers of crystals in parallel circles or

or the characteristics of the frequency-temperature circuits, ζ. B. five crystals in parallel circles

Relationship is essentially parabolic and or circuits, successful in practical experiments

which uses a so-called »reversal temperature«.

wise, d. H. a temperature corresponding to the A crystal form that is used when performing the

"Vertex" of the parabola, which can be used in the invention of the maximum frequency, is a crystal with

is equivalent to. These crystals with essentially 30 BT cut.

parabolic characteristics are considerably better. For high-frequency operation, the

regarding the complexity of the frequency-temperature crystals with high-frequency crystals of the F®-type

Law, and there are also some such double-twisted cuts, where Θ is the

Crystals from a lot or an item rotating angle about an axis which is in the X- Γ-plane

are taken, more similar in their behavior. 35 and is at an angle to the X-axis. Before-

Such crystals, however, are considerably more drawn crystals that fall under this term

frequency-dependent on the temperature, especially crystals with an RT cut; however, others can

when the temperature range is wide. Due to the crystals, especially crystals with IT cut,

essentially parabolic shape of the characteristic curve.

there is a slight change in frequency in 40. It is well known that the relationship between fre-

Dependence on the temperature only over a quenz (J), reversal frequency (J ₀ ), temperature (T ") and

limited temperature range around the reverse temperature reverse temperature (T ₀ ) by the following equation

rature reached. Outside this limited can be expressed:

Range, the frequency changes rapidly increasing f - f

or falling with temperature. If a grain 45 = -K (T - T ₀ ) ² .

compensation circuit in connection with one of the- ■ ':.

like crystal is required, it becomes undesirable. In the case of a crystal with a BT cut, this is complicated and expensive if the range above the typical value of K is 0.04; at a high frequency crystal with RT cut, however, a very limited range than the previously mentioned "limited range" can be achieved. 50 much lower value of JC can be achieved. Section with Θ = 15 ° and Θ = 34 ° 39 'temperature dependence of a quartz circuit arrangement - (designation according to the US Institute of Radio tion to provide two parallel branches, of which engineers') a Z value of 0.0066 can be achieved. The quartz in which this fact - the achievable low value one branch through a complicated process so 55 of K - is based the advantages of the invention, since it is produced that its frequency-temperature-dependent - approximately parabolic Frequency-temperature has the opposite sign compared to the characteristic curve of a high frequency crystal with other quartz bends "

The invention aims to provide an improved piezo than that of a BT cut crystal.

electrical crystal switchgear assembly can be created, 60 The invention will hereinafter be exemplified

which also when using crystals, of which hand the drawing is described; in this show

each one a substantially parabolic Fig. 1 and 3 explanatory graphs and

Frequency-temperature characteristic with one another FIG. 2 is a circuit diagram of an embodiment of the

has a similar course, a frequency-temperature invention.

Characteristic with considerably lower frequency 65 In F i g. 1, curves A and B show the frequency change in a wider range than temperature characteristics of two crystals A and B, this corresponding to the characteristic curve of a single one with a BT-cut, of which A alone a reversal of the structure would be possible. temperature of 27 ⁰ C and B alone is a reversal

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temperature of 75 ° C. In Fig. 1, F is the. where X _{0 is} the reactance of the entire circuit frequency and T is the temperature. These . capacitance (series connection of Cl and Cl combining two crystals are connected in two parallel circles ned crystal capacitance in the arrangement. A preferred oscillator switching arrangement, FIG. 2); L is the inductance of each crystal where a transistor is used as an active element, assuming that both become the same inductance, is in FIG. 2 shown. Each of these two have; β = ex.J ₀ , where α is the constant coefficient circles one with a resistance in addition to the parabola is under the assumption that both parabolas are the same adjustable inductance Ll or Ll ; / _c is the frequency of one of the crystals and capacitors Cl and Cl on which, if at the reversing temperature; T _x is half the temperature desired, can also be adjustable. The io turdiSerenz between the two reversal temperature values of the capacitors Cl and C2 are chosen such doors. Since the frequency-temperature curve (theod that a maximum flatness of the frequency-temperature retic) is parabolic
Characteristic of the combination is guaranteed, and f — f

the inductances Ll and Ll make it possible that the. = a. (T - T ₀ ) ² , (2)

Reversal frequency of each crystal to the required *

borrowed value can be set regardless of where J ₀ = frequency at the reversing temperature T ₀

My changes due to unavoidable and / = frequency at any temperature T,

Manufacturing tolerances. The circuit is designed so equation (1) allows to select crystals,

that curve B (Fig. 1) along the frequency axis for maximum compensation at each desired

to curve B 'is raised, so that the frequency to create ao frequency.

at the reversing temperature essentially at the- The following equation (3) results in

the same frequency as that of the curve. That is correct the frequency of the crystal combination and

Curves A and B ' are essentially symmetrical, making it possible to select crystals in order to

tric around the middle of the temperature range, d. H. to give desired compensated frequency / *,

the temperature of 51 ° C. The curves Dl, Dl 25 _

typify the resulting frequency-temperature. / * - / c + 3 ρ I _x , (3)

Characteristic curves of the overall circuit, which in arrangements From equation (1) it can be seen that the

of the type shown in Fig. 2 can be achieved. The compensation limit is reached when X _{0 is} so

The actually achievable in each individual case becomes large that the oscillator stops oscillating.

Curve depends on the exact design or calculation

decrease. The curve Dl, the mathematical frequency of which is determined by the crystal inductance

Analysis indicates that it is the maximum flattest curve at the frequency. BT cut crystals have one

is achieved by suitable selection of the partial values; relatively low inductance at 8 MHz, hence this

however, depending on the actually an advantageous frequency with respect to the compensation

selected partial values each curve of a family of curves, 35 sation. It has been found in practical trials to be

z. B. the curve D 3 can be achieved, which turned out approximately between possible, at this frequency below

the curves Dl and Dl lies. It can be seen that only two BT cut crystals are used

in none of the curves a large change in the parallel circles, the frequency constant ^{at 1:10 e}

Frequency is present with temperature and that is to be maintained over a temperature range of -26 to

the curve Dl the frequency very little with the 40 +66 ⁰ C.

Temperature fluctuates. The frequencies of this can be increased by increasing the number of crystals

The overall resulting curves are higher than those of even wider temperature ranges.

Curve A or B ' because of the modification of the switching. A calculation indicates that it is at 10.5 MHz

management parameters due to the presence of both is possible, a compensation of 1:10 ⁶ over

Crystals. It can be shown mathematically to achieve a range of -40 to 8O ⁰ C 45 by

that if in an oscillator one of two frequencies - use of three crystals in parallel circles,

zen at which it can oscillate, at which any small remaining changes in the

Frequency oscillates at which the series resistance frequency with temperature can be easily practical

is lower. eliminated if necessary by

In the embodiment according to FIG. 2 are 5 ° actually using one of the known compensations two series resonance circuits in parallel.

circuit in place, and at any given high frequencies will actually be very good ones Temperature is the oscillator frequency of the crystal obtained by using high-dependent, which has the lowest series resistance in frequency crystals of the Z © type with double-twisted results the temperature in question. In the middle 55 cuts, with the (9 rotation around an axis, Both crystals offer a temperature range (around 51 ° C) which lies in the X-7 plane, but at an angle substantially equal series resistances, and both are on the X-axis. A preferred form of contribute to the oscillator frequency. At a prak- crystals that fall within this term are table embodiment is the transition or the crystals with RT cut. F i g. 3 shows the frequency switching from one crystal to the other, using the 60 temperature curve of a typical crystal when the temperature is through the reversal BT-cut compared to that of a high-frequency tur moved, smooth and shock-free, and in practice it is crystals with RT cut; the one in solid line no noticeable discontinuity. curve shown is for the BT crystal and the point

The condition which must be fulfilled in order to achieve a + -uv ο α * t> _t y / c * 11 τ « η; _η τ , · "* ^d /

maximum flatness of the frequency-temperature characteristic curve for the RT crystal. In Fig. 3 -j-

line to achieve is plotted as the ordinate (J is the frequency), and the

Temperature T is plotted as the abscissa. It can be seen from Xc = _{-SnLßT x} ² , (1) that the dot- dash line curve is much flatter

than the curve in solid line. Every circuit according to the invention, in which crystals with BT cut are used, could equally well with crystals can be used with RT cut, the circuitry being the same and operating in the same way. as well IT cut crystals could be used.

The use of crystals with an RT cut has the advantage over the arrangements in which crystals with a BT cut are used that the temperature range over which the frequency is kept almost constant is considerably wider. Mathematical investigations show that it is possible to keep ^{the frequency constant at about 1:10 6} over a temperature range of -55 to 90 ^° C. even when using only two crystals with RT cut in parallel circles. The improvement that can be achieved by replacing high-frequency crystals with RT cut by crystals with BT cut is so pronounced that two crystals with RT cut in parallel circles give just as good, if not better results with regard to temperature constancy of the frequency than the one , which can be achieved with three crystals with BT cut in parallel circles.

The invention is of course not limited to the in Fig. 2 limited special circuit shown, but other and simpler circuits are also possible. There is only the simplest circuit from two parallel-connected branch lines, of which one only has one crystal and the other one contains a second crystal connected in series with a capacitor.

Claims (1)

Patent claims: -..- .: 1. Temperature-compensated piezo-electric Crystal circuit arrangement with more than one 35th crystal, each of which lies in a circle, the circuits being connected in parallel to one another, characterized in that the crystals have an at least approximately parabolic frequency-temperature characteristic curve with one another show a similar course and that with the crystals their individual reversal temperatures at essentially the same frequency, but at '. different temperatures occur, which are separated from each other in a temperature range to be covered.
2. Arrangement according to claim 1, characterized in that two parallel-connected circles are provided, one of which has a crystal and the other has a second crystal in series with a reactance which is designed so that the second crystal is its Reversal temperature at the same frequency as that of the first but at a different temperature. 3. Arrangement according to claim 1 or 2, characterized in that each crystal with an adjustable Inductance is connected in series. 4. Arrangement according to one of the preceding claims, characterized in that the Crystals exhibit BT cut. 5. Arrangement according to one of claims 1 to 3, characterized in that the crystals are high-frequency crystals of the Y ₀ type with double-twisted cuts, the rotation taking place around an axis which lies in the XF plane, but at an angle to the X axis. 6. Arrangement according to claim 5, characterized in that the crystals have RT cut. 7. Arrangement according to claim 5, characterized in that that the crystals have IT cut. 8. Arrangement according to one of the preceding claims, characterized in that the Circuit elements are designed so that they at least approximate the following equation fulfill X ₀ = -ZnLßTJ-, whereby Xe is the reactance of the total circuit capacitance, L is the inductance of a crystal,
T _x is half the temperature difference between the two reversal temperatures β = # / c, where oc is the constant coefficient of the parabola that gives the frequency-temperature curve of a crystal, / c is the frequency of one of the crystals at the reversal temperature. 1 sheet of drawings