Negative voltage generator for a semiconductor memory device
A negative voltage generator is controlled responsive to a word line precharge signal. Voltage fluctuations in a negatively biased word line scheme are reduced by using a kicker circuit to provide a predetermined amount of negative charge to shut off a word line during a precharge operation. The negative voltage generator includes first and second negative charge pumps. The second charge pump is activated responsive to the word line precharge signal. A negative voltage regulator can be used to regulate a negative voltage signal. A level shifter uses two voltage dividers and a differential amplifier to reduce response time, output ripple, and sensitivity to process and temperature variations. A negative voltage regulator cancels ripple from a charge pump to provide a stable negative bias voltage and reduce the amount of charge needed to precharge a word line.
1. A voltage generator configured to bias a word line from a boosted voltage having a first polarity to a second voltage having a second polarity, the voltage generator comprising:
a first charge pump having an output;
a second charge pump having an output coupled to the output of the first charge pump, wherein the second charge pump is adapted to be controlled by a precharge signal; and
a voltage regulator having an input directly coupled to the output of the first charge pump and an output directly coupled to the output of the second charge pump.
2. The voltage generator of claim 1 , wherein the output of the first charge pump is connected directly to the output of the second charge pump.
3. The voltage generator of claim 2 , further comprising: a voltage regulator having an input coupled to the outputs of the first and second charge pumps.
4. The voltage generator of claim 1 , further comprising:
a level detector having an input coupled to the output of the first charge pump.
5. The voltage generator of claim 1 , wherein the precharge signal is a word-line precharge signal.
6. A voltage generator configured to bias a word line from a boosted voltage having a first polarity to a second voltage having a second polarity, the voltage generator comprising:
first means for pumping charge to a voltage source;
second means for pumping charge to the voltage source, wherein the second means for pumping charge is adapted to be controlled by a precharge signal; and
means for regulating the voltage source, the means for regulating the voltage source having an input directly coupled to an output of the first means for pumping charge and having an output directly coupled to an output of the second means for pumping charge.
7. The voltage generator of claim 6 , further comprising:
means for detecting the voltage level of the voltage source.
8. The voltage generator of claim 6 , wherein the voltage source is a voltage source for negatively biasing a word line.
9. A voltage generator configured to bias a word line from a boosted voltage having a first polarity to another voltage having a second polarity, the voltage generator comprising:
an oscillator;
a first charge pump having an input coupled to the oscillator and an output for generating a first voltage responsive to an oscillating signal from the oscillator;
a voltage regulator having an input directly coupled to the output of the first charge pump and an output for generating a second voltage responsive to the first voltage; and
a second charge pump having an output directly coupled to the output of the voltage regulator, wherein the second charge pump is adapted to be controlled by a word-line precharge signal.
10. The voltage generator of claim 9 , further comprising:
a level detector having an input coupled to the output of the first charge pump and an output coupled to the oscillator.
11. The voltage generator of claim 9 , wherein the second charge pump is adapted to pump a predetermined amount of charge to the second voltage responsive to the word-line precharge signal.