Temperature compensating circuit

Temperature compensating circuit for an electronic timepiece having two piezo electric resonators having different frequency-temperature characteristics. Two piezo electric resonators are a major resonator having smaller frequency variation rate in temperature variation and a subsidiary resonator having larger frequency variation rate in temperature variation. And also the temperature compensating circuit includes a variable counter for counting the output signal of the major oscillator having the major resonator, a gate time setting circuit controlled by both the outputs of subsidiary and the variable counter, and a counter for counting the output signal of the major oscillator. As a result, the temperature compensating circuit is able to improve the accuracy of the timepiece.

BACKGROUND OF INVENTION 
The present invention relates to a temperature-compensating clock pulse 
generating circuit which generates temperature compensating clock pulses 
having a deviation of period within several tenth ppm. in a wide 
temperature range between, for instance, -50.degree. C. and 100.degree. C. 
The temperature compensating circuit is effective especially for a 
timepiece. Recently, an accuracy of a timepiece has been improved since a 
quartz crystal has been brought into use for a resonator, and the 
allowable range of error to prove the accuracy of the timepiece has been 
expressed as a monthly error and further it has been shifted to be 
expressed as an annual error. However, the timepiece which displays the 
time accurately to this extent has not been realized by a single quartz 
crystal resonator which is generally used at present. Accordingly, a wrist 
watch which displays time accurately by employing two resonators has been 
put into a practical use by the following two methods. (These methods are 
illustrated in detail in 9-18 issues, 1978 and 2-19 issues, 1979 of the 
"Nikkei Electronics") One method is to use two quartz crystal resonators A 
and B (referred to resonator hereafter) having negative secondary 
temperature coefficients. The secondary temperature coefficients of the 
resonators A and B are the same, the peak temperature of the resonator A 
is higher than B, and frequency at the peak temperature of A is lower than 
B. The characteristics of the two resonators A and B are set in order that 
the temperature characteristic of the resonator B at the high temperature 
side coincides with the peak frequency of the resonator B at the peak 
temperature of A. And beats of the resonators A and B having the 
characteristics correlated as illustrated above are extracted to produce 
various temperature compensating pulses in an electronic circuit on the 
basis of the beats, and a constant period pulse against time is extracted 
by inserting the compensating pulse. 
The other method is the conventional method in which two X-cut resonators 
having the same temperature characteristics and different peak 
temperatures are connected in parallel to act as one quartz crystal 
resonator equivalently. 
Both the two methods have the disadvantages in common. Namely, it is 
difficult to set the characteristics of the resonators act as one couple, 
i.e., it is necessary to further select a couple of resonators of within a 
certain tolerance. Therefore, the resonators, which in the nature of 
things, could have been housed in one case, cannot but housed separately. 
Moreover, the temperature range to be compensated, using a couple of 
resonators, is no more than around between 0.degree. and 50.degree., and 
this temperature compensating range is insufficient to assure the accuracy 
of the timepiece to the extent of the annual error of the time display 
under any areas and any circumstances. 
BRIEF SUMMARY OF INVENTION 
Accordingly, it is an object of the present invention to eliminate the 
above illustrated major disadvantages and to provide a temperature 
compensating circuit which can utilize not only the resonators having 
strictly limited feature but also the resonators having the other 
characteristics. 
Other and further objects, features and advantages of the invention will 
appear more fully from the following description.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIG. 1, there is shown a fundamental circuit block which 
achieves the object of the present invention, in which resonators 1 and 2 
are housed in the same case 3 in order to improve a thermal coupling. The 
resonator 1 is a major resonator and the resonator 2 is a subsidiary 
resonator. Both the resonators 1 and 2 have the negative secondary 
temperature coefficients. The temperature coefficient of the resonator 2 
is larger than the resonator 1, the peak temperature of the resonator 2 is 
lower than the room temperature and the frequency of the resonator 2 at 
the peak temperature is higher than that of the resonator 1. The peak 
temperature of the resonator 1 is near the room temperature. The X-cut 
resonator of 32 KHz is sufficient for the resonator 1. It is possible for 
the X-cut resonator presently disclosed and the other resonators to change 
the characteristics in accordance with the course as illustrated above, 
i.e., to increase the temperature coefficients and to reduce the peak 
temperatures. But it is very difficult to change the characteristics 
reversely, i.e., to decrease the temperature coefficients and to raise the 
peak temperature. Oscillators 4 and 5 respectively oscillate the resonator 
1 and the resonator 2. The output from the resonator 2 is fed to a gate 
time setting circuit 6, and the output from the resonator 1 is counted by 
a counter 7 at a gate time produced by the gate time setting circuit 6, 
and the counting value is N. The gate time set by the gate time setting 
circuit 6 is a time necessary to count k pieces of output pulses of the 
resonator 2. The concrete circuit structure of the gate time setting 
circuit will be illustrated later. 
Now the significance of the counting value N with respect to temperature 
will be illustrated. Arbitrary temperature of the resonators 1 and 2 is T, 
oscillating frequencies at the arbitrary temperature are respectively 
f.sub.1 T and f.sub.2 T, peak temperatures are respectively T.sub.1 and 
T.sub.2, secondary temperature coefficients .beta..sub.1 and .beta..sub.2, 
and tertiary temperature coefficients are .alpha..sub.1 and .alpha..sub.2 
in FIG. 1. If the gate time obtained by the gate time setting circuit 6 is 
the time taken to count K pieces of the outputs from the resonator 2, the 
counting value N is represented by the following formula. 
##EQU1## 
Namely N is a function with respect to the characteristics of the 
resonators 1 and 2 and the temperature T. The formula (1) is further 
developed to kf.sub.1 T-Nf.sub.2 T=0 . . . (2). And if an equation is set 
up with respect to T, AT.sup.3 +BT.sup.2 +CT+D=0 . . . (3), where 
A=kf.sub.1 .alpha..sub.1 -Nf.sub.2 .alpha..sub.2, B=kf.sub.1 (.beta..sub.1 
-3.alpha..sub.1 T.sub.1)-Nf.sub.2 (.beta..sub.2 -3.alpha..sub.2 T.sub.2), 
C=kf.sub.1 (3.alpha..sub.1 T.sub.1.sup.2 -2.beta..sub.1 T.sub.1)-Nf.sub.2 
(3.alpha..sub.2 T.sub.2.sup.2 -2.beta..sub.2 T.sub.2) and D=kf.sub.1 
(.beta..sub.1 T.sub.1.sup.2 -.alpha..sub.1 T.sub.1.sup.3 +1)-Nf.sub.2 
(.beta..sub.2 T.sub.2.sup.2 -.alpha..sub.2 T.sub.2.sup.3 +1). The values 
of A to D inclusive are determined by measuring the counting value N since 
the value varied according to the temperature T is only N. Therefore the 
value of T is found by expanding the equation (3), and f.sub.1 T is 
determined by substituting the value of T for f.sub.1 T=f.sub.1 
{1+.beta..sub.1 (T-T.sub.1).sup.2 +.alpha..sub.1 (T-T.sub.1).sup.3 }. . . 
(4). Though f.sub.1 T at an arbitrary temperature T is determined by 
adopting the regular method there is a problem for operating the root of a 
cubic equation T by an IC within a watch body since the area of IC 
enlarges and the power consumption increases. Therefore the method to find 
f.sub.1 T from the counting value N without finding the temperature T will 
be illustrated later. But the description will be continued on the 
assumption that f.sub.1 T have been found, temporarily. f.sub.1 T is found 
by an operation circuit 8 by the method mentioned later, and the value 
f.sub.1 T is maintained for a fixed period as the counting output. A 
counter 10 keeps counting receiving the oscillating frequency f.sub.1 T of 
the resonator 1 as an output. The oscillating frequency f.sub.1 T varies 
subjected to the temperature variation. The counted output connected by 
the counter 10 is compared with the counted output from the operation 
circuit 8 digitally by a comparator 9 for a fixed period of time. The 
comparator 9 produces the output to reset the counter 10 when both the 
counted outputs coincide. The reset counter 10 counts the oscillating 
output f.sub.1 T of the resonator 1 newly and repeats the same operation 
hereafter. Temperature of the output period T of the counter 10 
synchronized with the reset signal produced from the comparator 9 is 
compensated and becomes a fixed period against time. 
The principal mentioned above can be summarized as follows. The one output 
period of the counter is always fixed regardless of temperature by 
counting the number of pulses per a unit time varied by temperature 
because the capacity of the counter is changed corresponding to the 
temperature. 
Subsequently the time relation of each major signal in FIG. 1 will be 
illustrated by the time chart in FIG. 2. Each signal (a) to (e) inclusive 
in the time chart in FIG. 2 is the signal corresponding to (a) to (e) 
inclusive in FIG. 1, but (f) and (g) are not shown in FIG. 1. FIG. 2 shows 
each signal under the normal condition of the circuits in FIG. 1, and the 
circuit operation at start will be illustrated later. Duty cycles of 
pulses of each signal (a), (c), and (e) in FIG. 2 are drawn correctly for 
convenience of the drawing. The signals (a) and (c) in FIG. 2 are the 
outputs (a) and (c) of a couple of resonators in FIG. 1, both of which 
vary momentarily subjected to the temperature variation. The signal (b) in 
FIG. 2 is a period T(b) of the counter 10 in FIG. 1, the temperature of 
which is compensated, obtained by the method mentioned before. The signal 
(d) in FIG. 2 is the gate time (d) made in the gate time setting circuit 6 
in FIG. 1, which is obtained by the following method. 
The signal (c) in FIG. 2 is started counting just after the 
temperature-compensated period T(b) produced from the counter 10 in FIG. 
1, and the time corresponding to k pulses of the predetermined signal (c) 
is the gate time (d). A counting value N(e) in FIG. 2 is obtained by 
counting the signal (a) by the counter 7 in FIG. 1 during the gate time 
(d). The counting value N(e) is transmitted to the operation circuit 8 by 
the required number of bits, and the time taken to operate the required 
content by the operation circuit 8 is shown by the positive pulse width of 
the signal (f) in FIG. 2. The positive pulse width of the signal (g) in 
FIG. 2 indicates a wait time from the time the operation of the operation 
circuit 8 is over and the counting value is produced by the necessary 
number of bits until the counting value coincides with the counting value 
of the counter 10. 
Take note that it is not necessary to produce the counting value of the 
operation circuit 8 constantly during the time interval between the 
previous coincidence of the counting value of the counter 10 in FIG. 1 and 
the counting value of the operation circuit 8 and the next coincidence 
thereof. That is to say, the frequency variation range of the resonator 1 
in FIG. 1 is no more than several ppm order. Therefore, if the frequency 
is calculated on trial when the secondary temperature coefficient is 
-4.times.10.sup.-8 /.degree.C. estimating highly, (the tertiary 
temperature coefficient is ignored since it scarcely effects on the 
frequency), the peak temperature is 25.degree. C. and the frequency at the 
peak temperature is 32768 Hz, the frequency varying in the range between 
-50.degree. and 100.degree. C. is in the range between 32761 Hz and 32768 
Hz raising to an integer not lower than the decimal point, i.e., the 
former four figures 3276 are fixed in the above mentioned temperature 
range. The time taken to count 32768 pulses and the time taken to count 8 
pulses are in the ratio 4096:1, the other words, in the ratio 1:0.00024. 
If it takes one second to count 32768 pulses. 0.3 msec is enough to count 
8 pulses. The counting value of the operation circuit 8 and the counting 
value of the counter 10 coincide in the time interval of 0.3 msec, and the 
counting output of the operation circuit 8 in FIG. 1 is unnecessary during 
the former 0.9997 msec. 
By the reasons illustrated so far, the short time interval as the signal 
(g) in FIG. 2 is enough for the counting output of the operation circuit 8 
in FIG. 1. 
FIG. 3 shows an embodiment of the operation circuit 8, the comparator 9 and 
the counter 10 surrounded by dotted line in FIG. 1 more concretely, where 
the numerals corresponding to the numerals in FIG. 1 denote the same 
portions. AND circuits 13 and 14 are newly added. However, the digital 
pulse compensating method accompanies error of quantigation represented by 
1/f when the frequency is f. If the oscillation frequency of the resonator 
1 in FIG. 1 is f=32768 Hz, the resolution is no more than 30 ppm per one 
pulse. Therefore, in order to satisfy the conditions for practical use, if 
the temprature is compensated by 256 f, i.e., 8388608 pulses, the 
resolusion of 0.12 ppm per one pulse is obtained. Namely, if the 
oscillating frequency of the resonator 1 in FIG. 1 is f=32768 Hz and 
compared once 256 seconds, the number of pulses vary in 256 seconds as 
described above are between 8386816 and 8388608, i.e., the number of the 
fixed pulses are 8388608 and the variable pulses are 1792. If the pulses 
are converted into bits, the signals corresponding to eight bits vary and 
the remaining signals corresponding to fifteen bits can be fixed. If this 
condition is applied to the circuits in FIG. 3, the variable signals 
corresponding to eight bits are transmitted from the counter 10 to the 
comparator 9 as shown by the arrows and the fixed signals corresponding to 
fifteen bits are transmitted from the counter 10 to the AND circuit 13 as 
shown by the arrows. 
All the inputs fed to AND circuit 13 are the positive logic "1" from the 
nature of things when the fifteen bits signals fed to AND circuit 13 are 
the fixed value. It is not until the output from the AND circuit 13 is 
produced that AND condition is set by the output signal from the 
comparator 9 and AND circuit 14, and the counter 10 is reset by the output 
from the AND circuit 14 as shown. In this case the counting output of the 
operation circuit 8 is, of course, not more than eight bits. 
While the compensating method of the outputs from the resonator 1 in FIG. 1 
is selected according to the object. Namely, the output is compensated 
each one second period or each n seconds period collectively. 
If the method to compensate the output each n second period collectively is 
selected, the wavelength of the one second outputs of the counter 10 
slightly deviate from one second up to (n-1)th pulses influenced by 
temperature, and the error deviation up to (n-1)th pulses influenced by 
temperature is compensated collectively at n-th pulse. This method to 
compensate the output from the resonator 1 n pieces collectively is 
effective enough since the timepiece is a time integrating instrument. 
Subsequently the embodiment of the method to obtain the gate time by the 
gate time setting circuit 6 in FIG. 1 conceretely and the method to obtain 
the gate time (d) from the start condition that the period T(b) does not 
exist in FIG. 2, will be illustrated in conjunction with FIGS. 4 and 5. 
The circuits surrounded by a dotted line in FIG. 4 is an embodiment of the 
gate time setting circuit 6 in FIG. 1, and symbols (a) to (j) inclusive 
representing each signal correspond to the symbols in FIG. 1 to FIG. 5 
inclusive. The gate time setting circuit 6 comprises OR circuit 15, a 
trigger flipflop 16 (hereinafter referred to T.FF), AND circuit 17 and 
n-counter 18 and connection of each signal is as shown in FIG. 4. 
FIG. 5 shows time charts of each signal (b), (c), (d), (h), (i) and (j) 
inclusive in FIG. 4. T.FF 16, n-counter 18 in FIG. 4 and all sequential 
circuits in FIG. 1 are automatically reset for an instant after the power 
source is applied in order to zero the primary value. And the n-counter 18 
is reset by the signal at a low level, and conditions of T.FF 16 and the 
n-counter 18 change at the positive going waveform. If the power source is 
applied at t.sub.1 in FIG. 4 and FIG. 5, the power source is automatically 
reset at t.sub.2. In this condition only Q signal (d) of T.FF 16 is at a 
high level and the other signals are at a low level (hereafter a high 
level and a low level are respectively referred to H and L). The reset 
condition is removed at t.sub.3 and the resonator output (c) in FIG. 1 is 
fed at t.sub.4. (Since t.sub.1 to t.sub.4 inclusive are the operation at 
start for an instant, the waveforms in FIG. 5 do not correspond to each 
signal and the waveforms after t.sub.4 correspond to each signal). When 
the signal (c) is fed to n-counter 18 by way of AND 17, Qk output (h) of 
n-counter 18 becomes H, an output (i) of OR circuit 15 becomes H, Q-output 
(d) of T.FF 16 becomes L and an output (j) of AND circuit becomes L by the 
k-th signal (c) at t.sub.5, and when n-counter 18 is reset, Qk output (h) 
and OR circuit output (i) abruptly become L and the wedge pulses are 
produced. 
Thereafter the circuit condition of FIG. 4 cannot be changed except by the 
period T(b). The (j) output is generated by the signal of period T(b) 
produced by the counter 7, the operation circuit 8, the comparator 9 and 
the counter 10 after t.sub.5 as illustrated in FIG. 1. The signal of 
period T(b) is fed to an input of OR circuit 15 at t.sub.6 and transmitted 
to the output (i) of OR 15 as it is and reverses the output Q (d) of T.FF 
16 and removes a reset of n-counter 18 in FIG. 4, at the same time, the 
output (c) of the resonator in FIG. 1 is produced as the output (j) of AND 
circuit 17, and n-counter 18 turns the output (h) of Qk to H at k-th of 
the signal output (c). Thereafter the same operation is repeated. 
The time charts in FIG. 5 shows the operation of the gate time setting 
circuit 6 in FIG. 4. The gate time obtained by the gate time setting 
circuit in FIG. 4 is the signal (d) in FIG. 5. The gate time is not 
constant and varies according to temperature. As illustrated above, the 
gate time setting circuit operates smoothly from start condition. 
Subsequently the aforementioned "predetermined k pulses" will be 
illustrated. The predetermined k pulses corresponds to k in case n-counter 
19 in FIG. 4 is changed to k-counter, and k is the number of the signal 
(j) in FIG. 5 between t.sub.4 and t.sub.5. It means that the interval 
between t.sub.4 and t.sub.5 is the time for sampling the temperature and 
in order to elongate the time interval, it is necessary to enlarge k. The 
more k enlarges, the more the number of the signal (j) increases as well 
as the more the counting value N increases. By an increase in a counting 
value N, the temperature resolution goes up. The upper limitation of k is 
determined by the conditions that the interval between t.sub.5 and t.sub.6 
should be included in the interval between t.sub.4 and t.sub.6 of the 
signal (j). The other words, the operation period of the operation circuit 
8 in FIG. 1 and the wait period of the signal (g) in FIG. 2 should be 
included in the interval between t.sub.4 and t.sub.6 of the signal (j). 
Therefore k corresponding to the remaining time will be selected after the 
maximum variation range of the signals (f) and (g) in FIG. 2 are decided. 
Then the method to obtain f.sub.1 T from the counting value N will be 
illustrated. 
FIG. 6 is a characteristic diagram showing the relation between f.sub.1, 
f.sub.2, N and T in case f.sub.1 =32768 (Hz), .beta..sub.1 
=3.times.10.sup.-8 (.degree.C..sup.2).sup.-1, .alpha..sub.1 
=-1.times.10.sup.-10 (.degree.C..sup.3).sup.-1, T.sub.1 =25(.degree.C.), 
f.sub.2 =33000 (Hz), .beta..sub.2 =-6.times.10.sup.-8 
(.degree.C..sup.2).sup.-1, .alpha..sub.2 =-1.times.10.sup.-10 
(.degree.C..sup.3).sup.-1 and k=7800000. FIG. 7 is a characteristic 
diagram showing the relation between f.sub.1 T, T and N revising the 
relation of FIG. 6. The relation of f.sub.1 T=F(N) is approximated by 
developing the formula of Taylor's series. Although the degree of the term 
to be developed is determined by the requird precision, it is sufficient 
to develop the formula to the third degree practically. If f.sub.1 T=F(N) 
is approximated to the third degree of the term, f.sub.1 T=AN.sup.3 
+BN.sup.2 +CN+D. Four absolute terms from A to D inclusive are obtained by 
measuring the values of N and f.sub.1 T by the counter at four arbitrary 
temperatures. 
If the values N and f.sub.1 T at the four arbitrary temperatures Ta, Tb, Tc 
and Td are respectively Na, Nb, Nc, Nd, f.sub.1 Ta, f.sub.1 Tb, f.sub.1 Tc 
and f.sub.1 Td, the following biquadratic simultaneous equations of four 
elements are respresented. 
EQU f.sub.1 Ta=N.sup.3 aA+N.sup.2 aB+NaC+D 
EQU f.sub.1 Tb=N.sup.3 bA+N.sup.2 bB+NbC+D 
EQU f.sub.1 Tc=N.sup.3 cA+N.sup.2 cB+NcC+D 
EQU f.sub.1 Td=N.sup.3 dA+N.sup.2 dB+NdC+D 
And by developing the following 4 lines and 4 rows, A, B, C and D are 
obtained. 
##EQU2## 
If A, B, C and D are determined, f.sub.1 T is determined by f.sub.1 
T=AN.sup.3 +BN.sup.2 +CN+D. In order to raise the precision of f.sub.1 T 
more, it is effective to apply the minimum binary system by multiplying 
the measuring points. The precision at the arbitrary temperature is not 
necessary for this measuring method but it is sufficient to fix the 
arbitrary temperature, and f.sub.1 T of high precision is realized since 
the measuring value is N and the frequency is f.sub.1 T. To tell more 
concretely, if f.sub.1 T is approximated by a cubic equation, f.sub.1 T is 
obtained by f.sub.1 T=AN.sup.3 +BN.sup.2 +CN+D. 
FIG. 8 is a frequency-temperature characteristic diagram showing 
substantially a fixed temperature characteristics in a wide range obtained 
by the temperature compensating circuit applying the principle of the 
present method. 
Lastly the relation of the frequency tuning will be illustrated. The 
counting outputs of the operation circuit 8 in FIG. 1 should be integers 
and fractions should be omitted, raised to a unit or rounded to the 
nearest whole number. FIGS. 9 and 10 are the correlation diagrams between 
the fundamental frequency and the temperature characteristics in which 
fractions are treated differently, where the abscissa shows the ambient 
temperature, the ordinate shows the amount of deviation from the reference 
frequency indicated by ppm, c represents a reference frequency, a 
represents the amount of plus deviation from the reference frequency, b 
represents the amount of minus deviation from the reference frequency. 
Both a and b have certain widths in order to show the range of 
quantigation error. FIG. 9 shows the deviation of the temperature 
characteristics in case fractions are omitted, in which the amount of plus 
deviation is larger than the amount of minus deviation. The rate of the 
plus deviation and the minus deviation is reversed in case fractions are 
raised to a unit (not shown). FIG. 10 shows the deviation of the 
temperature characteristic in case fractions are rounded to the nearest 
whole number. This figure is preferable since the amount of plus deviation 
and the amount of minus deviation is substantially the same. Then 
terminals 11 and 12 attached to the operation circuit 8 in FIG. 10 will be 
illustrated. 
As illustrated before, though f.sub.1 T is obtained by f.sub.1 T=AN.sup.3 
+BN.sup.2 +CN+D, the f.sub.1 T value may be varied by constructing the 
circuit so that the D value may change arbitrary by switch operation of 
the terminals 11 and 12. If the D value enlarges, the reference 
frequencies of FIG. 11 are changed from a to b and b to c, and the 
frequency can be adjusted. 
As illustrated in detail hereinbefore, by applying the present method, the 
following advantages are obtained in comparison with the conventional 
method: 
1. The temperature compensating range is wider than the conventional 
method. 
2. Since the degree of the freedom of the characteristics of the two quartz 
resonator is high, the tuning of the characteristics as a couple is 
unnecessary, as a result the productivity becomes high. 
3. Since all the signals are representated digitally, this method is 
suitable for applying to an IC. 
4. This method can be adopted to various resonators. 
Although the embodiments of the present invention applied to the X-cut 
resonator have been illustrated, it is possible to apply to the other 
resonator having different characteristics.