Power supply voltage detection circuit

Details Power supply voltage detection circuit Power supply voltage detection circuit

2002-01-24

2004-02-03

Tran, Toan (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Synchronizing

C327S077000, C327S307000

Reexamination Certificate

active

06686782

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a power supply voltage detection circuit for outputting a signal upon detecting a power supply voltage, and more particularly to an improvement thereon for preventing the signal from being erroneously output due to a sharp rise of the power supply voltage.
Referring to FIG.
19
and
FIG. 20
, a power supply voltage detection circuit
103
designed to detect a power supply voltage based on a predetermined voltage is typically used as a reset signal generation circuit for an arithmetic circuit
102
in a semiconductor integrated circuit
101
, for example. Typically, when the power supply voltage is lower than or equal to a predetermined voltage Vo, the power supply voltage detection circuit
103
determines that the power supply voltage is not detected and thus outputs a ‘not detected’ signal to inactivate the arithmetic circuit
102
, whereas when the power supply voltage is higher than the predetermined voltage Vo, the power supply voltage detection circuit
103
determines that the power supply is detected and thus outputs a ‘detected’ signal to activate the arithmetic circuit
102
. In this way, the semiconductor integrated circuit
101
is operated properly.
Referring to
FIG. 21
, the power supply voltage detection circuit
103
includes a voltage division circuit
130
for outputting a signal of an output voltage A, a reference voltage circuit
131
for outputting a signal of a reference voltage B, and a comparison circuit
132
for comparing the output voltage A from the voltage division circuit
130
with the reference voltage B from the reference voltage circuit
131
. The voltage division circuit
130
includes two resistors
113
serially connected between the power supply terminal and the ground terminal for linearly dividing the power supply voltage so as to output the output voltage A, which is the voltage at the division point. Since the output voltage A from the voltage division circuit
130
is a voltage obtained through a resistance-based division of the power supply voltage, the output voltage A changes in proportion to the power supply voltage, as illustrated in FIG.
22
A. On the other hand, the reference voltage B from the reference voltage circuit
131
is defined to be equal to the output voltage A when the power supply voltage is equal to the predetermined voltage Vo, and the reference voltage B in its steady state is constant irrespective of the power supply voltage. Typically, when the output voltage A is lower than or equal to the reference voltage B, based on the comparison at the comparison circuit
132
, it is determined that the power supply voltage is lower than or equal to the predetermined voltage Vo so as to output the ‘not detected’ signal (low signal L in the illustrated example), whereas when the output voltage A is higher than the reference voltage B, it is determined that the power supply voltage is higher than the predetermined voltage Vo so as to output the ‘detected’ signal (high signal H in the illustrated example). Thus, the waveform of the output voltage A and the waveform of the reference voltage B cross each other at a position where the power supply voltage is equal to the predetermined voltage Vo so as to form an intersection at the crossing point, so that the output signal is switched from one to another when crossing the intersection.
While the reference voltage circuit
131
is typically designed to output a reference voltage signal simultaneously with the rise of the power supply voltage, it takes a certain amount of time that is determined by the circuit configuration of the reference voltage circuit
131
before the reference voltage circuit
131
starts outputting a stable, constant reference voltage B. For example, where a band gap reference circuit is used as the reference voltage circuit
131
, it takes a certain amount of time that is determined by the feedback circuit before the band gap reference circuit starts outputting a stable, constant voltage signal. If the power supply voltage rises sharply, the output voltage A may rise over, without crossing, the reference voltage B, thus forming no intersection between the waveform of the output voltage A and the waveform of the reference voltage B, as illustrated in FIG.
22
B. In such a case, the power supply voltage detection circuit
103
always outputs the ‘detected’ signal (high signal H) without outputting the ‘not detected’ signal (low signal L), thereby failing to reset the semiconductor integrated circuit
101
.
In the prior art, this problem has been addressed by adding a resistor
104
and a capacitor
105
to the power supply terminal external to the semiconductor integrated circuit
101
, as illustrated in
FIG. 19
, or by adding a capacitor
105
having a large capacitance to the power supply terminal external to the semiconductor integrated circuit
101
, as illustrated in FIG.
20
. In this way, even when the power supply voltage rises sharply, the rise of the power supply voltage is gentle for the power supply voltage detection circuit
103
in the semiconductor integrated circuit
101
, thereby ensuring that the ‘not detected’ signal (low signal L) is output when appropriate.
However, when the resistor
104
and/or the capacitor
105
are provided external to the circuit, as in the conventional power supply voltage detection circuit
103
, those external components increase the system cost and the mounting area.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a power supply voltage detection circuit for outputting a signal upon detecting the power supply voltage by comparing, at a comparison circuit, an output voltage from a voltage division circuit with a reference voltage from a reference voltage circuit, with an improvement being made to the inside of the circuit such that it is ensured that a ‘not detected’ signal is output when appropriate even when the power supply voltage rises sharply, without using external components which would otherwise increase the system cost and the mounting area.
In order to achieve the object, in one embodiment of the present invention, a signal to be input from the voltage division circuit to the comparison circuit is canceled or delayed until the power supply voltage reaches a predetermined voltage during the rise of the power supply voltage. Alternatively, in one embodiment of the present invention, the operation speed of the voltage division circuit is suppressed so as to slow down the rise of the output voltage. Alternatively, in one embodiment of the present invention, the unstable state of the reference voltage during the rise of the power supply voltage is utilized, by fixing the output signal of the power supply voltage detection circuit itself while the reference voltage is unstable.
Specifically, in one embodiment of the present invention, a power supply voltage detection circuit includes a voltage division circuit, a reference voltage circuit and a comparison circuit, wherein a second voltage is predetermined, and the power supply voltage detection circuit further includes signal cancellation means for canceling an input of an output voltage signal from the voltage division circuit to the comparison circuit when the power supply voltage is lower than the second voltage, while not canceling the input of the output voltage signal when the power supply voltage is higher than the second voltage.
In this way, during the rise of the power supply voltage, even if there is a period in which the input voltage from the voltage division circuit to the comparison circuit is lower than the reference voltage from the reference voltage circuit, whereby the output voltage from the voltage division circuit rises over, without crossing, the reference voltage during a sharp rise of the power supply voltage, the input voltage at the comparison circuit rises gently. Therefore, it is ensured that a ‘not detected’ signal is output when appropriate. When the power supply voltage is higher than the second voltage, the cancellation operation by

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