DE1954068B2 - Oscillator circuit with a parallel resonance crystal - Google Patents

Description

The invention relates to an oscillator circuit with a parallel resonance crystal and with an active one Element of the oscillator representing the first field effect transistor with an isolated control electrode, with a resistor connected in series with the field effect transistor, one between the control electrode this transistor and the end of the resistor facing away from it arranged quartz oscillator as well as with a capacitive voltage divider, which is connected in parallel to the quartz oscillator and its Output is connected to the junction of the transistor with the resistor.

The invention aims at realizing a quartz oscillator circuit, which can be carried out in miniaturized form, in particular at least partially as an integrated (printed) circuit, and which is capable with very little power to generate a periodic signal of a particularly stable frequency.

These two conditions then gain their full significance. if such a quartz oscillator circuit the time base of an electronic meter. especially a wristwatch, represents

ίο which is known to be a series of frequency divider stages for the signal generated by the Gazilki gate circle as well as an electromechanical transducer, which runs through this frequency divider in the frequency reduced signal is fed and is used to drive the gear train of the clock.

An oscillator is known (Electronics from 3rd! 0.66, P. 07, J. Pa η i co "FET stabilizes amplitude of Wien bridge oscillator"), in which with the help of the rectified output voltage is controlled by a field effect transistor. the one in an oscillator circuit affects the amplitude of the generated vibrations. The signal from this oscillator is wise its shape is stable as long as its frequency is not higher than O.i MHz. This oscillator that is no A quartz oscillator and its frequency constancy is much lower than that of such, contains a relatively large number of high-ohmic resistances and des'.alb a relatively high one Power consumption. This property, based on its structure, makes the oscillator unsuitable for a miniaturized, especially integrated design. Further, it is because of the presence of many high-resistance resistors are very temperature-sensitive, and the voltages required for its supply are also very temperature-sensitive way too high. to be able to be supplied by a battery of small dimensions. The aforementioned Properties of these known oscillators make them unsuitable for use as a Timebase door an electronic precision clockwork, especially for that of a wristwatch.

As is well known, there are quartz oscillators that work with quartz shear oscillators. These show little signs of aging. are not very sensitive to shock and can be processed that their temperature coefficient remains constant over a sufficiently large temperature range and compensates for the temperature coefficient resulting from the actual oscillator circuit.

This type of quartz is therefore particularly suitable for use in a wristwatch. However, it is to point out that the energy consumption of an oscillator containing such a quartz is only under the condition is low. that one lets the Qaarz work in parallel resonance in the circle. aside from that must, if the consumption of the oscillator when supplying an alternating voltage in the order of magnitude of a volt should not exceed a few μW, the capacity that the oscillator circuit for the Quartz represents to be very small, i.e. H. of the order of magnitude the static capacity of the quartz itself.

In the well-known, so-called three-point oscillator circuits, to which both the Colpitts oscillators as well as the one mentioned at the beginning, which became known through the US Pat. No. 3,213,390 Belong to the oscillator, you only need a single transistor, which forms the active element of the circuit, to ensure that the vibration is maintained

Afford. Now the transistor in these circuits must have at least 7 poles at points in the circuit connected, which have a high impedance for the oscillation frequency. This fact then has a particularly disturbing effect; <us. if the oscillator is to use very little energy. because at least one of the impedances mentioned must be traversed by the current, which for the Transistor is needed to meet the vibration conditions. These are of great value Impedance can be that of a coil, a connected circuit or a contradiction be of high ohmic value.

Given the small amount of space available in a watch, the use of a coil or connected circuit is not highly recommended, and they ^; -i also not very economical.

Using a resistor with a higher ohmic value would mean using a higher one Supply voltage to achieve the door make the transistor indispensable direct current necessary, which of course would lead to a proportionate considerable loss of power occurs in this resistor

If, on the other hand, a resistor with a low ohmic value is used, the resistance due to the AC voltage of the oscillator output lost. going performance relatively high.

The batteries that are common today and can be inserted into the case of a wristwatch are relatively small Dimensions can only have very weak and low voltage energy provide what, of course, the possibility of using a resistor of high ohmscheyi value excludes. Using a resistor of low ohmic value would consume one lead very large proportion of the energy available in the battery in the oscillator, as this Almost all of the energy used to power the frequency divider and the time display device of the watch should be determined.

It is also necessary to point out that the amplitude of the oscillator circuit of the The type of output signal described, the value of which is determined by the electronic control of this oscillator Circuits, e.g. B. Frequency divider circuits. is set by a very simple middle! adjustable is.

The invention is based on the object of an oscillator circuit with a parallel resonance crystal to train the type specified so that a particularly low energy consumption, even with Powered by a low voltage power source, very low temperature and shock sensitivity as well as good manufacturability in miniaturized, integrated design are made possible.

According to the invention, this object is achieved in an oscillator circuit of the type specified at the beginning solved in that the resistor is formed by a second field effect transistor with an insulated control electrode is arranged in series with the first field effect transistor, and that they have one with the Control electrode of the second transistor contains connected voltage generator, the one for operation this TransL'or supplies sufficient voltage in the saturation area.

The transistors used in this oscillator circuit are advantageously those from the 'carrier enrichment' <or "enhancemenU" type. whose through-flow is known to be extraordinary is weak. when their control voltage is zero. what the realization of an oscillator circuit of allows very low energy consumption.

In order to stabilize the periodic output from the oscillator circuit Signal with a view to stabilizing the frequency of this signal can be the aforementioned control voltage generator be formed by an amplifier, which is one of the output signal of the oscillator circuit derived signal is controlled and via its output to the control electrode of the

if, second transistor is connected.

It is useful if the amplifier has a resistor and a third field effect transistor with an insulated control electrode, which is connected in series with a Speiseg'eichspannungsquelle are, wherein the control electrode of the third transistor with the junction of two one Voltage divider for the ■ supplied by the oscillator circuit periodic Spannvig forming capacitors and the connection point of the resistor with the third transistor is connected to the control electrode of the second transistor.

For example, the drawing illustrates
Fig. 1 shows the scheme of a quartz oscillator circuit with parallel resonance / known type,

2 shows the circuit diagram of a quartz oscillator circuit with parallelreso.ian? according to one embodiment the invention.

FIGS. 3 and 4 are explanatory diagrams and

F i g. 5 shows the diagram of a variant of the one shown in FIG. 2 illustrated embodiment Circuit.

The oscillator circuit shown in Fig. 1 contains a field effect transistor T ₁ with an isolated control electrode, a resistor R ₁ . which is arranged in series with this transistor and with a DC voltage source P. a voltage divider formed by two capacitors C ₁ and C ₂ and arranged between the control electrode of the transistor T ₁ and the positive pole of the DC voltage source P , the connection point of the capacitors C ₁ and C ₂ with the connection point of the resistor R ₁ and the transistor T, is connected, a quartz Q, the two electrodes of which are connected to the two ends of the voltage divider C ₁ and C ₂ . A resistor R ₂ ensures the polarization of the transistor T ₁ . The resistor R ₁ helps to determine the amplitude of the periodic signal supplied by the oscillator _{at the terminals α and cj 2} , which are connected to one and the other electrode of the crystal Q, respectively.

Fs has already been shown (cf. for example Hising: "Quartz Crystals for electrical circuits". D. Van Nostrand). that the in a quartz

needed power the same

X ¹

2 K _n

is. where V is the

Amplitude of the alternating voltage applied to the quartz and R ₁ , the parallel equivalent resistance of the quartz.

This resistance R _p is given by the relationship

(C ₀ + Cr) ² R,

with

«Ι = angular frequency,
C ₀ = static capacity of the quartz,
C ₇ - = total capacity that the circuit for the

Quartz represents
R _e = series equivalent resistance of the quartz.

The capacitance C ₀ is for a quartz oscillating at a frequency of a few MHz, e.g. B. of the order of 1 to 2 pF, while the capacitance C ₇ - of a classic oscillator circuit is 10 to 30 pF. The value of this capacity is comparatively important; it follows that the parallel equivalent resistance of the quartz is small, resulting in a large amount of power consumed in the quartz.

V ¹
This power is actually greater than y _R -,

because in addition to the parallel _{equivalent resistance R n} there is on the one hand an equivalent resistance R 'originating _{from the resistance R 1, so that}

is, and on the other hand the resistor R ₂ . so that the total power consumed is the same:

P =

V ² 2 R _n

Yl

'2R ₂

The resistor R ₂ can have a very high ohmic value, which is a neglect of the

V ¹
Expressive , “ allowed.

In order for this power P to be particularly small, the oscillator circuit would have to have a very small capacitance C _T and a very large ear resistance R 'at the same time.

That would only be possible when using a high supply voltage, namely because of the _{current required for the transistor T 1} for the correct functioning of the oscillator circuit, which would preclude the use of such an oscillator circuit in all cases in which the supply by a small Battery tablet takes place, such as. B. when an oscillator circuit of the type shown is determined to the time base of an electronic clockwork small dimensions, z. B. an electronic wrist watch to form.

The in F i g. 2, which is very simple in terms of its structure, allows the oscillator circuit. This deficiency can be remedied and, with the exception of the quartz, the trimmer Tr and possibly the resistors R ₃ and R _4, can be easily implemented in an integrated form so that the capacitance of the circuit can be kept at a particularly low value.

In this circle, the one from FIG. 1 apparent resistance R, replaced by a second field effect transistor T ₂ with an insulated control electrode, to which a polarization voltage is applied, which has a sufficient value to bring this transistor into the saturation range for the current flowing through it. This voltage is taken from the junction of the two resistors R ₃ and R ₄ , which are arranged in series with the power source and represent a voltage divider. The frequency of this oscillator circuit is set using the trimmer Tr.

F i g. 3 shows the change in a field effect transistor with an insulated control electrode flowing through it Current depending on the supply voltage and for a certain value of the polarization voltage applied to this electrode.

ίο The output resistance is in the saturation range,

d r

the so-called saturation resistance, equal to ^ -: he

becomes very large for small currents.
When the electronic components of the oscillator circuit shown are implemented in an integrated form and when, as a result, the capacity of the circuit is small. the current flowing through the transistor T ₂ is very small and therefore the saturation resistance is very large. This is particularly advantageous because, for this reason, the value of the above-mentioned resistor R 'itself is very large, so that the values generated by the oscillator circuit according to FIG. 2 power consumption is very low.
For example, the feed current of an oscillator circuit according to FIG. 2, which serves as the time base of an electronic clock, is of the order of magnitude of 1 μΑ. For such a low current, the saturation resistance of a field effect transistor can assume a value of 100 MU and more, which allows the influence of the power consumed by the quartz Q to be neglected in the power balance. It can also be shown that in an oscillator circuit of this type the amplitude of the alternating voltage on the quartz is directly proportional to the current flowing through _{the transistors T 1} and T _2. so that it is possible to adjust the alternating voltage on the quartz by suitably controlling the current flowing through _{the transistor T 2.}

In Fig. 2, V are ₁ . V ₂ and V are the alternating voltage amplitudes between points a ₃ and Ci ₁ . a ₂ and a ₃ . a ₂ and a _{x of} the circle occur: V ₃ is the DC control voltage of transistor T ₂ . i is the direct current flowing through _{the transistors T 1} and T _2.

As can be seen, the saturation current i ₅ and the control voltage V _{c of} a field effect transistor with an isolated control electrode are connected by the relationship:

i _s = K (V _r -V ^ ² .

where K is the steepness of the transistor in AV ² and V ,. is its threshold voltage.

This relationship is usually established as in FIG. 4, which shows the change in yX as a function of V _e .

If the control voltage V _{e has} a sinusoidal curve, as z. B. for the transistor T, the

If so, the current flowing through it is evidently a periodic current, the peak value i _{p of} which corresponds to the maximum value of this voltage V _e (FIG. 4). The curve of the periodic current can be converted into a Fourier series can be decomposed so that one can write _{for the transistor T 1:}

= L

954068

the amplitude of the basic component of the current,

the peak current,

the value of the angle between the instants at which the saturation current is maximum reached, and the one in which this current has become zero.

b) ί =

where i = direct current component of the current, and the values / ((9) and ψ (θ) are derived from a Fourier decomposition of the current curve, as described. One can also write:

c) V ₂ = UR.,

where R _{n is} the impedance between points a ₃ and Q ₁

d. H. after combining the relationships a) and c):

nid by combining b) and d): f [H)

e) V ₁ = ι- K ₀

J)
ψ {θ) '

If the capacitance of the capacitors C ₁ and C ₂ z. B. is such that C] = C ₂ , from which V ₁ = V _{2 is} derived. the amplitude of the voltage 1 'is the same

ie:
g) V = i-

40

2 ' ψ (θ)' (R '+ R ₂ ") ·

Basically, (■) can be between 0 and 180 ".

fifi \
which for - ~ üji results in a value between 2 and 1.33.

Under normal working conditions for the oscillator circuit described, (-) is equal to 90 ^c and

vW) ~ '' ^ ' ^so ^^ ^ ^e amplitude of the alternating voltage on the quartz becomes:

K ₂

55

This amplitude is effectively proportional to the _{current flowing through the transistors T 1} and T ₂ , the magnitude of which can be determined by acting on the control voltage V _{3 of} the transistor T ₂ . as we know this current by the relationship already given above

i = K ₂ (V ₃ -V, /

defined, in which V = threshold voltage of transistor T ₂ , K ₂ = steepness of transistor T ₂ .

In the case of the oscillator circuit according to FIG. 2, the amplitude of the periodic signal generated by it is fixed one door every time via the voltage divider which contains the resistors K ₃ and R ₄ and on which the value of the control voltage of the transistor T ₂ depends.

The variant according to FIG. 5 makes it possible to obtain a more or less perfect stabilization of the amplitude of the periodic signal obtained at the terminals of the crystal, with the control voltage of the transistor T _{2 being} appropriately controlled, as will be described below. A stabilization of the signal amplitude is in fact highly desirable, especially in the area of the implementation as an integrated circuit, since the input capacitance of this type of transistors as well as the capacitance of the connection points of the various components are known to depend on the applied voltage.

According to the invention it is provided that this control is implemented with the aid of an amplifier which is controlled by a signal derived from the output signal of the oscillator circuit and _{acts on transistor T 2 in} such a way that each time the amplitude of this output signal increases, this output signal decreases proportionally of the current flowing through this transistor and vice versa. This counteraction makes it easy to achieve a particularly good stabilization of the amplitude of the signal generated by the oscillator circuit.

Since the polarization _{voltage of the transistor T 2} must be a direct voltage, it is necessary that the output of the Osziiiatorkreixe; obtained to rectify the amplifier controlling voltage or that the output voltage of this amplifier is rectified.

In the embodiment variant of the circle shown in FIG. 5, the second of these made use of both possibilities.

This amplifier consists of a field-effect transistor with an isolated control electrode and a resistor R ₃ connected in series with the current source P and a capacitive _{capacitor C 3} and C ₄ connected in series between the output terminals α and a _{2 of} the oscillator circuit containing voltage divider can be controlled. A clamping diode D determines the DC voltage in point d. If the peak-mushroom voltage at this point reaches a _{magnitude corresponding to that of the threshold voltage of the transistor T 3} , the resulting Stroi.i in this transistor causes the voltage across the resistor K ₃ to drop, resulting in a well-defined value of the control voltage of the transistor T ₂ leads. This voltage is the lower or the more reduced, as the control voltage of the transistor T _{3 is} increased, ie. the amplitude of the alternating voltage signal emitted by the oscillator circuit is considerable or low. In this way, the _{current flowing through the transistors T 1 and T 2 is} regulated to the value corresponding to the desired voltage at the quartz, which is well determined by the ratio of the capacitances of the capacitors C ₃ and C _{4 of} the voltage divider to which the Control electrode of transistor T _{3 is} connected and through the threshold voltage of this transistor

The rectification of the control of the transistor T _; required voltage is realized in the present case by the transistor T ₃ , where eir

Capacitor C ₅ suppresses the alternating components of the output voltage of the amplifier formed _{by this transistor and the resistor R 3.}

The whole of the components denoted by the reference numeral T _1, T _2, T _2, C _U C _2, C _3, C _4, C ₅ and D can be easily performed in an integrated construction.

Of course, the amplifier _{formed by the transistor T 3} and the resistor R _{3 could} , as a variant, be of different properties without deviating from the invention.

The oscillator circuit described is intended to be fed by a mercury oxide or silver battery P, the excellent voltage stability of which is known. Since, on the other hand, the signal amplitude generated by this oscillator circuit is particularly well stabilized in the manner described, it follows that the quartz oscillator circuit according to the invention has a very high stability with regard to the frequency of the generated signal with very little power consumption.
The transistors used in the circuits described are of the P-type; of course, the same circuits could be made with N-type transistors, simply reversing the polarities of the supply source of each circuit.

Although in the above description of the

ίο Oscillator circuit in connection with an application was explained in the field of timekeeping, such a circle can very well be used in others Use areas, especially in all cases in which the constancy of amplitude and frequency of the generated signal is a particularly important condition, as is the energy requirement at the same time should be one of the least possible.

1 sheet of drawings

Claims (4)

Patent claims: 1. Oscillator circuit with a parallel resonance crystal and with a first field effect transistor with an isolated control electrode, which represents the active element of the oscillator, with a resistor connected in series with the field effect transistor, an oscillating crystal arranged between the control electrode of this transistor and the end of the resistor located away from it, and with a capacitive voltage divider which is connected in parallel to the quartz oscillator and whose output is connected to the connection point of the transistor with the resistor, characterized. that the resistance is formed by a second field effect transistor (T ₂ ) with an insulated control electrode, which is arranged in series with the first field effect transistor (T ₁ ). and that it contains a voltage generator ( P. R ^. R ₄ ; P, R ₃ , T _3. C _3. C ₄ ) connected to the control electrode of the second transistor (T ₂ ), "the one for the operation of this transistor in the Saturation range provides sufficient voltage. 2. Oscillator circuit according to claim 1, characterized in that the transistors (T ₁ -T,) are of the carrier enrichment or "enhancement" type. 3. Oscillator circuit according to claim 1, characterized in that the voltage generator is formed by a / amplifier which is controlled by a ^{signal derived from the Ausgan ^ ssignr 1 of} the Gszillaurkreises and via its output with the control element ¹ trode of the second transistor (T ₂ ) connected is. 4. Oscillator circuit according to claim 3, characterized in that the amplifier _{comprises a resistor (R 3} ) and a third field effect trinsistor (T ₃ ) with an isolated control electrode, which are connected in series with a Speisegieichspannurgsquelle (P), wherein the control electrode of the third transistor (T ₃ ) with the connection point (ä) _{of two capacitors IC ,, C 4} ) forming a voltage divider for the ρ odic voltage supplied by the oscillator circuit and the connection point of the resistor (R,) with the third transistor (T ₃ ) with the Control electrode of the second transistor (7 ₂ ) is connected.