Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-06-26
2001-11-20
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
Reexamination Certificate
active
06320457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a high level voltage generator, and more particularly to a high level voltage generator for rapidly pumping a high voltage node by simultaneously driving two high voltage pumping circuit when the potential level of the high voltage node is largely dropped.
2. Description of the Related Art
In general, a semiconductor memory device such as DRAM is a random access memory which reads/writes data in/from a memory cell including a transistor and a capacitor. The read or write operation of the DRAM will be described as follows. First, a row address strobe signal /RAS becomes in an active state and then a word line is activated by a row address signal. Then a column address strobe signal /CAS becomes in an active state and a bit line is activated by a column address to select a memory cell. The data is read/written in/from the selected memory cell.
The DRAM uses a high level voltage Vpp having a higher level than the power supply Vcc considering the voltage loss due to a threshold voltage Vtn of the MOS transistor constituting the memory cell in driving a word line. The high level voltage Vpp is generated from a high level voltage generator for a word line which generates a potential of power supply Vcc+threshold voltage Vtn+&Dgr;V.
FIG. 1
shows a conventional high level voltage generator. The high level voltage generator includes a high voltage level detection means
100
which detects a potential level of a high voltage node Vpp and compares the detected level with the target level to generate a pumping enable control signal ppe. The high level voltage generator includes a ring oscillator
200
for periodically generating a pulse signal by the pumping enable control signal ppe from the high voltage level detection means
100
in a power-up signal of active state and a high voltage pump means
300
for pumping the high voltage node to a high voltage level by the pulse signal from the ring oscillator
200
. The high level voltage generator further includes a power-on precharging circuit (not shown) for initializing the potential level of the high voltage node Vpp to a constant voltage, before the high voltage pump means
300
operates.
The operation will be described as follows. First, in a power-up initial state, before the high voltage pump means
300
operates, if the potential level of the high voltage node Vpp is lower than an external voltage Vext, the power-on precharing circuit (not shown) initialize the high voltage node Vpp to a voltage which is lower than the external voltage Vext by a threshold voltage Vt of a MOS transistor. Thereafter, a power is supplied to a DRAM device, the substrate voltage pump circuit (not shown) operates and pumps the substrate voltage Vbb below a constant voltage. At this time, if the substrate voltage Vbb is below a constant voltage, the power-up signal is applied to the ring oscillator
200
to generate the pulse signal having a constant period.
The high voltage pump means
300
pumps the high voltage node Vpp to rise the potential level of the high voltage by the pulse signal from the ring oscillator
200
. The high voltage level detector
100
detects whether the potential level of the high voltage node Vpp reaches to the target level. If the detected potential level of the high voltage node Vpp reaches to the target level, the high voltage level detection means
100
makes the ring oscillator
200
not to generate the pulse signal. Accordingly the high voltage pump means
300
does not more operate.
The high level voltage generator constantly establishes the pumping drivablity in the high voltage pump means
300
. When the consumption of the high voltage is large, the pumping time becomes long. Otherwise, when the consumption of the high voltage is low, the pumping time becomes short. Therefore, so as to reduce the pumping time, if the high level voltage generator is designed to have the large drivability, the potential level of the high voltage node is rapidly recovered. However, during the required time that the high voltage level detection means
100
detects the potential level of the high voltage node Vpp to control the high voltage pump means
300
, the high voltage pump means
300
continuously operates. Accordingly, the potential level of the high voltage node Vpp exceeds the initial target level.
Accordingly, so as to reduce the pumping time, if the prior high level voltage generator is designed to have the large drivablity in the high voltage pump means
300
, the high voltage level is rapidly recovered. But the undesired current consumption becomes large and the noise caused. On the other hand, so as to reduce the current consumption and the noise, if the high level voltage generator is designed to have the low drivability in the high voltage pump means
300
, the recovery time of the high voltage level becomes long and data in a memory cell becomes lost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a high level voltage generator with increase of operation speed and reduction of current consumption by adjusting the drivability in a high voltage pump circuit in accordance with the potential level of the high voltage.
According to an aspect of the present invention, there is provided to a high level voltage generator, comprising: high voltage level detection means for comparing a potential level of a high voltage node and a target level to generate a first pumping enable control signal; first oscillation means for periodically generating a first pulse signal by the first pumping enable control signal from the high voltage level detection means; first high voltage pump means for pumping the potential level of the high voltage node by the first pulse signal from the first oscillation means; pumping drivability control means for detecting a length of an active time of the first pumping enable control signal to generate a second pumping enable control signal; second oscillation means for generating a second pulse signal by the second pumping enable control signal from the pumping drivablity control means; and second high voltage pump means for pumping the potential level of the high voltage node by the second pulse signal from the second oscillation means.
In the high level voltage generator, the pumping drivability control means includes a delay part for delaying the first pumping enable control signal from the high voltage level detection means for a constant time; and an AND logic part for carrying out AND logic operation of an output signal from the delay part and the first pumping enable control signal. The delay part includes an even number of inverters and the AND logic part includes a NAND gate and an inverter.
In the high level voltage generator, the first and second oscillation means are comprised of ring oscillators.
According to another aspect of the present invention, there is provided to a high level voltage generator, comprising: high voltage level detection means for comparing a potential level of a high voltage node and a target level to generate a first pumping enable control signal; oscillation means for periodically generating a pulse signal by the first pumping enable control signal from the high voltage level detection means; first high voltage pump means for pumping the potential level of the high voltage node by the pulse signal from the oscillation means; pumping drivability control means for detecting a length of an active time of the first pumping enable control signal to generate a second pumping enable control signal; pulse transfer means for transferring the pulse signal from the oscillation means by the second pumping enable control signal from the pumping drivablity control means; and second high voltage pump means for pumping the potential level of the high voltage node by the pulse signal transferred from the pulse transfer means.
In the high level voltage generator, the pumping drivability control means includes a delay part for delaying the first pumping enable control signal fr
Hyundai Electronics Industries Co,. Ltd.
Pillsbury & Winthrop LLP
Zweizig Jeffrey
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