Miscellaneous active electrical nonlinear devices – circuits – and – External effect – Temperature
Reexamination Certificate
2002-03-18
2004-04-06
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
External effect
Temperature
Reexamination Certificate
active
06717457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and a temperature change detecting device. More particularly, the present invention relates to a semiconductor device including a processing circuit which needs temperature compensation to provide intended functions properly, and to a temperature change detecting device which detects changes in the temperature of an object of interest.
2. Description of the Related Art
It is known that the characteristics of electronic circuit components formed on a semiconductor substrate have some temperature dependence. On-chip resistors, for example, show variations in the resistance when the temperature changes. For this reason, the cutoff frequency of an active filter implemented on a semiconductor chip would vary with the substrate temperature if its temperature-sensitive elements were not corrected appropriately.
Researchers have proposed various temperature compensation methods to address the above problem.
FIG. 10
shows a conventional compensation circuit where one such method is implemented. The illustrated circuit is composed of a first constant current source
10
, an internal component
11
, a second constant current source
12
, an external component
13
, a voltage difference detector
14
, and a circuit
15
that needs temperature correction. These circuit elements are formed on a semiconductor device, except for the external component
13
.
The first constant current source
10
supplies the internal component
11
with a constant current. The internal component
11
is, for example, a resistive element formed as part of the semiconductor device. The second constant current source
12
supplies the external component
13
with a constant current. The external component
13
is another resistive element placed outside of the semiconductor device so as not to be affected by the temperature of the device.
The voltage difference detector
14
senses the voltage difference between the internal component
11
and external component
13
and creates a n-bit signal representing that difference. This signal is supplied to the circuit
15
(e.g., active filter) which needs temperature compensation.
The circuit of
FIG. 10
operates as follows. Upon power up, the first and second constant current sources
10
and
12
begin to supply a constant current to their respective load circuits
11
and
13
, the former being located inside the device and the latter being located outside the device. Consider, for example, that the constant current sources
10
and
12
, internal components
11
, and external component
13
are designed to produce zero volts as a voltage difference between the upper nodes of the internal component
11
and external component
13
at room temperature (25 degrees Celsius). Since this condition holds during a certain period immediately after the device is powered up, the voltage difference detector
14
supplies the circuit
15
with a n-bit signal indicating that no voltage difference is detected. With this n-bit signal, the circuit
15
applies a prescribed signal processing function (e.g., filtering) to the given input signal with its default circuit parameters.
Suppose that a certain time has passed and the temperature of the semiconductor device has risen. While the temperature of the internal component
11
rises accordingly, the external component
13
located outside the semiconductor device stays at the same temperature. If the internal component
11
and external component
13
have a positive temperature coefficient (i.e., their resistances go up with temperature), the internal component
11
will exhibit a larger resistance than the external component
13
. This means that the voltage developed across the internal component
11
will be greater than that of the external component
13
(assuming that the two constant current sources
10
and
12
output the same amount of current).
The voltage difference detector
14
now detects a non-zero voltage difference between the internal component
11
and external component
13
and creates a n-bit signal representing that difference for delivery to the circuit
15
. Suppose that the voltage drop of the internal component
11
is 5.2 volts while that of the external component
13
is 5.1 volts. The voltage difference detector
14
then notifies the circuit
15
of the voltage difference by sending an n-bit signal representing that value, 0.1 volts.
The circuit
15
corrects itself with reference to the n-bit signal received from the voltage difference detector
14
. Since it is 0.1 volts in the present example, the circuit
15
controls an integral resistive element in such a way that its resistance will be reduced to cancel out the temperature-induced increase. By doing so, the circuit
15
can maintain its own operating characteristics even if the device temperature is increased.
The conventional configuration explained above in
FIG. 10
, however, needs a mounting space for the external component
13
other than the semiconductor device itself. This is a disadvantage under some circumstances where the space limitation is tight. Another problem of the conventional circuit is that the output current of the constant current sources
10
and
12
may change with temperature because of the temperature dependence of circuit components used in them. This means that a measurement error would be introduced to the detected difference voltage.
Referring next to
FIG. 11
, another example of a conventional temperature compensation method will be shown. The illustrated circuitry comprises a circuit
20
, a subtractor & integrator
21
, an evaluation circuit
22
, a resistance controller
23
, and a clock generator
24
.
The circuit
20
is an active filter composed of resistors, capacitors, integrators, and other elements. The subtractor & integrator
21
integrates the voltage developed across one of the resistors in the circuit
20
. It subtracts a DC offset from that voltage, if any, so as not to include such an offset in the result of integration.
The evaluation circuit
22
compares the output of the subtractor & integrator
21
with a predetermined reference signal and passes the result to the resistance controller
23
. According to the comparison result, the resistance controller
23
controls the value of a certain resistive element that governs the characteristics of the circuit
20
. The clock generator
24
provides the subtractor & integrator
21
and evaluation circuit
22
with a clock signal since they use switched-capacitor techniques.
The circuit of
FIG. 11
operates as follows. When the semiconductor device is powered up, the circuit
20
starts to operate as an active filter. Timed with respect to the clock signal supplied from the clock generator
24
, the subtractor & integrator
21
integrates the voltage developed across a particular resistor in the circuit
20
and sends the result to the evaluation circuit
22
. The integration result contains no DC offset component of the voltage of interest because the subtractor & integrator
21
rejects it before integration.
The evaluation circuit
22
compares the output signal of the subtractor & integrator
21
with a predetermined reference signal and passes the result to the resistance controller
23
. Suppose, for example, that these two signals agree with each other at room temperature (25 degrees Celsius). The evaluation circuit
22
then notifies the resistance controller
23
of the agreement between the two signals since the device temperature is almost the same as the ambient temperature just after power-up. While it is designed to modify the value of a certain resistive element in the circuit
20
according to the comparison result, the resistance controller
23
does nothing to the circuit
20
at the moment since the difference value has been observed to be zero.
As the time has passed after power-up, the temperature of the resistive element of interest goes up with the device temperature, causing a variation of the circuit paramet
Minobe Kenichi
Nanba Hiromi
Arent & Fox PLLC
Zweizig Jeffrey
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