Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synchronizing
Reexamination Certificate
2002-06-03
2002-12-10
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synchronizing
C327S198000
Reexamination Certificate
active
06492850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit having a power supply circuit that generates an internal supply voltage using an external power supply voltage, and a method for generating the internal supply voltage in the semiconductor integrated circuit.
2. Description of the Related Art
Recently, portable equipment driven by batteries has come into wide use. It is requested that a semiconductor integrated circuit mounted in the portable equipment is of a low power consumption specification in order to ensure a long life of the batteries. In many cases, this type of a semiconductor integrated circuit has a voltage generator that generates an internal supply voltage whose voltage is lower than an external supply voltage by using the external supply voltage supplied from the outside thereof, and low power consumption has been achieved by supplying the internal supply voltage into predetermined circuits. Recently, a semiconductor integrated circuit is internally provided with a plurality of voltage generators, wherein a plurality of kinds of internal supply voltage is respectively supplied into the major circuit blocks.
FIG. 1
shows an example of the major circuits to generate an internal supply circuit in a semiconductor integrated circuit.
A reference voltage generator
1
has a current-mirror circuit
1
a,
and generates reference voltage VREF by using an external supply voltage VEXT. A power-on reset circuit
2
inactivates a power-on reset signal POR (that is, to make the power-on reset signal enter a lower level) when the external supply power VEXT exceeds a predetermined value. The current-mirror circuit
1
a
has a function by which the reference voltage VREF is forcibly made into the external supply voltage VEXT upon receiving a high-leveled power-on reset signal POR. The reference generator
1
generates the reference voltage VREF, following the external supply voltage VEXT, by the power-on reset signal POR when the external supply voltage VEXT is low and the reference voltage VREF cannot be generated by the current-mirror circuit la. That is, the reference voltage VREF can be steadily generated where the external supply voltage VEXT is low.
A voltage generator
3
has a differential amplifier
3
a
composed of a current-mirror circuit, and a regulator
3
b
composed of a pMOS transistor. The differential amplifier
3
a
controls the regulator
3
b
upon receiving the reference voltage VREF and the fed-back internal supply voltage VINT. The regulator
3
b
generates an internal supply voltage having predetermined drive capacity.
An example in which the reference generator is controlled by the power-on reset signal POR is disclosed in Japanese Unexamined Patent Application Publication No. Hei-130170.
However, the current supply capacity of supply voltage VEXT generated by batteries is lower in comparison with the current supply capacity of general power supplies. Therefore, for example, when the respective circuits of semiconductor integrated circuits mounted in portable equipment operates as a whole when the power is turned on, there are cases where the supply voltage VEXT is temporarily lowered.
FIG. 2
shows the voltage waveform when the supply voltage VEXT is lowered.
As the external supply voltage VEXT is temporarily lowered when the power is turned on, the differential amplifier
3
a
of the voltage generator
3
shown in
FIG. 1
does not operate normally, and a feedthrough current occurs. Resultantly, such a problem occurs, by which the internal supply voltage VINT does not rise to a normal level. In particular, the above-described problem is likely to occur where the differential amplifier
3
a
is composed of a CMOS circuit. The reason resides in that the external supply voltage VEXT supplied is required to be greater by two or more times than the threshold voltage of a transistor in order to steadily actuate the differential amplifier
3
a
(current-mirror circuit). That is, the CMOS differential amplifier has a smaller operating margin at its low voltage side.
Further, generally, in a semiconductor integrated circuit mounted in portable equipment, the operational voltage is reduced in order to lower the power consumption (For example, the external supply voltage is 2.5V). Since the threshold voltage of the transistor scarcely depends on the external supply voltage, the ratio of the threshold voltage of the transistor to the external supply voltage VEXT is increased, wherein the above-described problem is still likely to occur.
In addition, as shown in
FIG. 2
, the timing of generation of the internal supply voltage VINT shifts, wherein as the power-on reset signal POR is inactivated (going to a low level) before the internal supply voltage VINT is raised to a normal voltage, circuits that are required to be reset in the semiconductor integrated circuit will be activated before a normal internal supply voltage VINT is supplied. As a result, these circuits are not correctly reset, there is a possibility of the portable equipment being hung up.
On the other hand, as described above, the reference voltage generator
1
generates the reference voltage VREF, following the external supply voltage VEXT, by a power-on reset signal POR when the power is turned on. However, when the voltage generator
3
for receiving the reference voltage VREF has a CMOS differential amplifier
3
a,
the voltage generator does not operate normally in a region where the external supply voltage VEXT is low even if the voltage generator
3
receives the reference voltage VREF following the external supply voltage VEXT. Therefore, the voltage generator
3
cannot generate a normal internal supply voltage VINT.
SUMMARY OF THE INVENTION
An object of the present invention is to reliably generate an internal supply voltage when an external supply voltage supplied to a semiconductor integrated circuit is low and, in particular, to quickly raise the internal supply voltage following the external supply voltage when the power is turned on.
Another object of the present invention is to securely generate an internal supply voltage in a voltage generator having a CMOS current-mirror circuit even when the supply voltage supplied to the CMOS current-mirror circuit is low.
Still another object of the present invention is to reliably reset an internal circuit supplied with the internal supply voltage.
According to one of the aspects of the semiconductor integrated circuit in the present invention, the semiconductor integrated circuit has a voltage generator and a power-on circuit. The voltage generator generates an internal supply voltage supplied to internal circuits under control of the reference voltage by using an external supply voltage supplied from the exterior. The power-on circuit inactivates a power-on reset signal which resets at least one of the internal circuits (predetermined internal circuit(s)) when both the external supply voltage and the internal supply voltage exceed a predetermined value. The voltage generator forcibly supplies the external supply voltage as the internal supply voltage when the power-on reset signal is activated. Therefore, the internal supply voltage is generated following the external supply voltage when the external supply voltage is low and the voltage generator does not normally operate as in the case where the power is turned on.
According to another aspect of the semiconductor integrated circuit in the present invention, the voltage generator has a differential amplifier and a regulator. The differential amplifier outputs a differentially amplified signal upon receiving the reference voltage and a voltage that fluctuates depending on the internal supply voltage. Under control of the output of the differential amplifier, the regulator generates an internal supply voltage by using the external supply voltage. Since the power-on reset signal controls the differential amplifier or the regulator, the regulator is forcibly turned on when the power-on reset signal is activated. As a result
Kato Yoshiharu
Wakasugi Nobuyoshi
Arent Fox Kintner Plotkin & Kahn
Cunningham Terry D.
Fujitsu Limited
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