Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2001-03-12
2003-07-29
Wachsman, Hal (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S060000, C365S185180, C365S185230
Reexamination Certificate
active
06601003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a low power-supply voltage detection circuit, and more particularly to a low power-supply voltage detection circuit for detecting low power-supply voltage when a drop occurs in the power-supply voltage that is supplied to a nonvolatile memory.
2. Description of the Related Art
In the prior art, an internal high voltage is generated from the power-supply voltage by means of a booster circuit in order to write data or erase a page in nonvolatile memory.
The current-voltage characteristic of the internal high voltage generated from the booster circuit is dependent on the power-supply voltage, the internal high voltage typically increasing and the current supply capability improving with increase in the power-supply voltage. Conversely, decrease in the power-supply voltage results in lower internal high voltage and poor current supply capability.
When writing data and erasing pages at a power-supply voltage that is lower than operation specifications, the internal high voltage often fails to attain an adequate current-voltage characteristic, whereby incorrect data are written or data are corrupted. At a low power-supply voltage that does not ensure data writing or page erasing, control is effected such that data writing or page erasing in a nonvolatile memory is suspended.
FIG. 1
is a circuit diagram of a low power-supply voltage detection circuit disclosed in Japanese Patent Laid-open No. 8599/1989 that detects low power-supply voltage in order to exercise this type of control. This low power-supply voltage detection circuit comprises: resistor
901
and zener diode
902
connected together in series between power-supply voltage Vcc and ground; resistors
903
and
904
that are connected together in series between ground and the connection point of resistor
901
and zener diode
902
; resistors
905
and
906
that are connected together in series between power-supply voltage Vcc and ground; comparator
907
; and booster circuit
908
.
The fixed voltage that is taken from the connection point of resistor
901
and zener diode
902
is voltage-divided at resistors
903
and
904
and supplied as a reference voltage to one of the input terminals of comparator
907
. On the other hand, voltage obtained by voltage-dividing the power-supply voltage from the connection point of resistors
905
and
906
is led out and supplied to the other input terminal of comparator
907
. Comparator
907
compares this voltage-divided voltage with the reference voltage, outputs high level to booster circuit
908
when the voltage-divided voltage is higher than the reference voltage, and outputs low level to booster circuit
908
when the voltage-divided voltage is equal to or lower than the reference voltage.
Power is thus not supplied to booster circuit
908
if the power-supply voltage is equal to or lower than a prescribed value, and operations such as data writing to the nonvolatile memory are halted.
However, even in cases in which the nonvolatile memory is operating at an adequate power-supply voltage, there are cases in which power-supply voltage undershoot occurs in which the power-supply voltage drops for an extremely short interval. In this case, the low power-supply voltage detection circuit detects the low power-supply voltage regardless of whether the operation of the nonvolatile memory is affected or not, and operations such as data writing are subjected to unpredictable halts. As shown in
FIG. 2
, with each occurrence of undershoot of the power-supply voltage, the output of comparator
907
switches to low level and operations such as data writing to a nonvolatile memory are halted. This phenomenon tends to occur when the operating power-supply voltage of the nonvolatile memory is low, or in a state in which a read operation is carried out in parallel with a write operation or an erase operation, such as when performing parallel operations such as a dual read. The same also holds true for a case of operating a charging-pump booster circuit at a low power-supply voltage and supplying a high current such as in CHE (Channel Hot Electron) mode flash memory.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a low power-supply voltage detection circuit that is capable of detecting low power-supply voltage without suspending such operations as data writing during instances of power-supply voltage undershoot of extremely short duration.
The low power-supply voltage detection circuit of the present invention detects drops in the power-supply voltage that is supplied to a nonvolatile memory that is capable of performing data writing and/or page erasing when a memory control signal is active, and comprises: a reference voltage generation means; a power supply voltage dividing means; a comparison means; and a low power-supply voltage control means.
The reference voltage generation means generates and outputs a fixed voltage as a reference voltage. The power supply voltage dividing means divides a voltage between the power-supply voltage and ground voltage and outputs this voltage as a voltage-divided voltage. The comparison means compares the reference voltage and voltage-divided voltage, turns the low power-supply voltage signal OFF when the voltage-divided voltage is higher than the reference voltage, and turns the low power-supply voltage signal ON and outputs the signal when the voltage-divided voltage is lower than the reference voltage. The low power-supply voltage control means effects control such that a memory control signal switching operation is either halted or enabled for a prescribed time interval; the memory control signal switching operation being an operation in which a memory control signal is activated and output when this low power-supply voltage signal is OFF and switched from active to inactive when the low power-supply voltage signal changes from the OFF state to the ON state.
The nonvolatile memory should be capable of performing at least one of data writing and page erasing, and be capable of switching between activity and inactivity of these operations by means of an input signal. A general-purpose flash memory can therefore be employed.
The reference voltage generation means can be constituted by generally used circuits such as a combination of zener diodes and resistors. A variety of circuits, such as an amplification circuit for amplification and output, can be used according to the specifications of the nonvolatile memory.
The power supply voltage-dividing means may be constituted by a generally known circuit. For example, a plurality of resistors may be connected together in series between the power supply line and ground and voltage then extracted from connection points between the resistors.
When voltage-dividing the power-supply voltage, the value of the voltage-divided voltage may be adjusted such that the ratio of the reference voltage to the voltage for performing the memory control signal switching operation is the same as the ratio of the voltage-divided voltage to the power-supply voltage. Of course, the value of the reference voltage may also be varied and adjusted.
The comparison means should have the functions of receiving and comparing the above-described reference voltage and voltage-divided voltage and switching the level of the output signal according to the size of the voltage-divided voltage with respect to the reference voltage, and a general-purpose comparator may therefore be used. The output signal is applied to the low power-supply voltage control means as the low power-supply voltage signal. Here, a circuit for dealing with hazards for preventing erroneous operation halts may be added to the low power-supply voltage signal output.
Since the ratio of the reference voltage to the voltage for performing the memory control signal switching operation is the same as the ratio of the voltage-divided voltage to the power-supply voltage, the level of the low power-supply voltage signal is switched according to the size of the actual p
NEC Electronics Corporation
Wachsman Hal
Young & Thompson
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