Miscellaneous active electrical nonlinear devices – circuits – and – External effect – Temperature
Reexamination Certificate
1999-09-21
2001-06-19
Nuton, My-Trang (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
External effect
Temperature
Reexamination Certificate
active
06249173
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an LSI circuit, and more particularly to a temperature stabilizing circuit adapted to stabilize the junction temperature of an LSI.
2. Description of the Related Art
A conventional timing generator (hereinafter referred to merely as “a T. G.”, when applicable) made up of a CMOS gate array is so designed that, in the case where it is used in an LSI tester, the user can change an operating frequency every cycle at the time of measurement.
This will be described with reference to the drawing in detail.
FIG. 6
is a block diagram showing a conventional T. G. made up of a CMOS gate array.
FIG. 7
is a diagram indicating junction temperature and tpd in a conventional T. G. The term “tpd” as herein used is intended to mean a time difference between an input signal applied to a T. G.
61
shown in FIG.
6
and an output signal outputted by the T. G.
61
. The thermal resistance of the package is 7.5° C./W, the power consumption is 1 W, and the peripheral temperature is 25°.
In
FIG. 7
, at the time instant t
60
, the supply voltage of the LSI is an optional one. Next, when at the time instant t
62
the operation is stated with 1 &mgr;s, then the junction temperature becomes 32.5° C. at the time instant t
63
. On the other hand, the tpd becomes 810 ps from 770 ps; that is, the tpd increases by 40 ps. Next, when at the time instant t
64
the operation is started with 100 ns, then at the time instant t
65
the junction temperature becomes 47.5° C., while the tpd becomes 850 ps. Furthermore, when at the time instant t
66
the operation is started with 10 ns, then at the time instant t
67
the junction temperature becomes 100° C., while the tpd becomes 1 ns.
In the prior art, as was described above, the T. G.
61
made up of the CMOS gate array is mounted on an LSI tester. When the user changes the operating frequency in one test, the power consumption is changed, the junction temperature is changed, and the tpd is greatly changed. And, if the tpd is greatly changed with time, the jitter value is increased, and the rated value of the LSI tester becomes worse. For instance, in
FIG. 7
, with the operating frequencies of 1 &mgr;s and 10 ns, the jitter value is 230 ps. As is apparent from the above description, when the operating frequency of the T. G.
61
changes, the operating current is changed, and the junction temperature is changed. And the tpd of the T. G.
61
changes, and the jitter value, which is important for the LSI tester, becomes more than the rated value.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the invention is to provide a temperature stabilizing circuit which stabilizes the junction temperature of a timing generator made up of a CMOS gate array, and decreases the jitter value.
In order to achieve the foregoing object, according to the invention, there is provided a temperature stabilizing circuit comprising:
reference temperature obtaining means for obtaining a reference pulse number corresponding to the junction temperature under the condition that the junction temperature of an LSI reaches the highest value;
operating temperature obtaining means for obtaining an operating pulse number according to the junction temperature of the LSI when the LSI is in an ordinary operating state; and
current control means which, when the LSI is in the ordinary operating state, controls the operating current of the LSI so that the operating pulse number of the operating temperature obtaining means be equal to the operating pulse number of the reference temperature obtaining means.
According to a second aspect of the invention, there is provided the temperature stabilizing circuit of the first aspect of the invention, further comprising: signal forming means for forming a signal having a period corresponding to the junction temperature of the LSI according to a pulse signal of fixed period which is applied to the LSI;
wherein the reference temperature obtaining means comprises a first counter which, with the junction temperature at the highest temperature, counts the pulse signal of fixed period with the period of a signal formed by the signal forming means, and
wherein the operating temperature obtaining means comprises a second counter which, the LSI in an ordinary operating state, counts the pulse signal of fixed period with the period of a signal formed by the signal forming means.
According to a third aspect of the invention, there is provided the temperature stabilizing circuit of the first aspect of the invention wherein the current control means comprises:
a comparison circuit which compares the operating pulse number provided by the operating temperature obtaining means with the reference pulse number provided by the reference temperature obtaining means; and
current control circuit for increasing or decreasing the operating current to the LSI according to the difference between the reference pulse number and the operating pulse number which is provided by the comparison circuit.
In the invention, the reference temperature obtaining means obtains the reference pulse number corresponding to the junction temperature with the junction temperature of the LSI at the highest value. For instance, the signal forming means forms a signal having a period corresponding to the junction temperature of the LSI on the basis of the pulse signal of fixed period which is applied to the LSI; and with the junction temperature at the highest the first counter counts the aforementioned pulse signal of fixed period with the period of the signal formed by the aforementioned signal forming means, thereby to obtain the reference pulse number.
In the ordinary operating state, the operating temperature obtaining means obtains the operating pulse number corresponding to the junction temperature of the LSI during the normal operation. For instance, the second counter counts the aforementioned pulse signal of fixed period with the period of the signal which, in the normal operating state of the LSI, is formed by the signal forming means, thereby to obtain the operating pulse number. And, during normal operation, the current control means controls the operating current of the LSI so that, during normal operation, the operating pulse number of the operating temperature obtaining means be equal to the reference pulse number of the reference temperature obtaining means.
For instance, the comparison circuit subjects the reference pulse number of the reference temperature obtaining means and the operating pulse number of the operating temperature obtaining means to comparison, and the current control circuit increases or decreases the operating current flowing to the LSI according to the difference between the reference pulse number and the operating pulse number which is obtained by the comparison circuit. That is, if the operating pulse number is larger than the reference pulse number, the amount of current of the current control circuit is increased thereby to increase the junction temperature; on the other hand, the operation pulse number is smaller than the reference pulse number, the amount of current of the current control circuit is decreased thereby to decrease the junction temperature. Hence, the junction temperature is stabilized, and the jitter value is decreased.
REFERENCES:
patent: 4587478 (1986-05-01), Kasperkovitz et al.
patent: 5440520 (1995-08-01), Schutz et al.
patent: 5723998 (1998-03-01), Saito et al.
patent: 6049221 (2000-04-01), Ishibashi et al.
Ando Electric Co. Ltd.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Nuton My-Trang
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