High voltage generator and related flash memory device
A high voltage generator includes a charge pump generating a high voltage in response to a pumping clock signal, a charge/discharge circuit responsive to the pumping clock signal and charging the high voltage to generate an output voltage, a comparator for comparing the output voltage with a reference voltage to generate a comparison result, and a clock modification circuit adjusting a pumping slope of the charge pump in relation to the comparison result, wherein the clock modification circuit reduces the pumping slope when the high voltage reaches a target voltage level.
1. A high voltage generator comprising:
a charge pump generating a high voltage in response to a pumping clock signal;
a charge/discharge circuit responsive to the pumping clock signal and charging the high voltage to generate an output voltage;
a comparator for comparing the output voltage with a reference voltage to generate a comparison result; and
a clock modification circuit adjusting a pumping slope of the charge pump in relation to the comparison result, wherein the clock modification circuit reduces the pumping slope when the high voltage reaches a target voltage level.
2. The high voltage generator circuit of claim 1 , wherein the clock modification circuit reduces the pumping slope of the charge pump by at least one of changing a pulse width for the pumping clock signal, adjusting a frequency of the pumping clock signal, or adjusting an amplitude of the pumping clock signal.
3. The high voltage generator circuit of claim 2 , wherein the clock modification circuit reduces the pumping slope of the charge pump in relation to a first and second phase of the pumping clock signal.
4. The high voltage generator circuit of claim 1 , wherein the clock modification circuit comprises:
a first inverter inverting a clock signal;
a control circuit responsive to the comparison result and adjusting the speed with which the clock signal applied to the first inverter is inverted; and
a second inverter inverting the output of the first inverter to generate the pumping clock signal.
5. The high voltage generator circuit of claim 1 , wherein the clock modification circuit reduces the pumping slope by changing a driving capacitance value associated with the charge pump.
6. The high voltage generator circuit of claim 5 , wherein the clock modification circuit comprises:
a plurality of capacitors and a corresponding plurality of switches,
wherein each one of the plurality of capacitors is selectively connected to a corresponding capacitor associated with the charge pump through a switching operation applied to the plurality of switches.
7. The high voltage generator circuit of claim 1 , wherein the charge/discharge circuit comprises:
a first charge/discharge circuit charging the high voltage received from the charge pump in response to a first phase of the pumping clock signal and generating the output voltage in response to a second phase of the pumping clock signal; and
a second charge/discharge circuit supplying the output voltage from the first charge/discharge circuit to the comparator in response to the second phase of the pumping clock signal.
8. The high voltage generator circuit of claim 7 , wherein the first charge/discharge circuit comprises:
a first high voltage switch outputting the high voltage in response to the first phase of the pumping clock signal;
a first capacitor charging the high voltage received from the first high voltage switch; and
a second high voltage switch outputting a voltage charged in the first capacitor as the output voltage in response to the second phase of the pumping clock signal.
9. The high voltage generator circuit of claim 8 , wherein the second charge/discharge circuit includes:
a second capacitor outputting a voltage from the second high voltage switch to the comparator; and
a discharge switch discharging a charged voltage in the second capacitor to ground in response to the first phase of the pumping clock signal, during a charging period of the first capacitor.
10. A flash memory device comprising:
a memory cell array having a plurality of memory cells arranged in word lines and bit lines; and
a high voltage generator circuit generating a high voltage supplied to a selected word line and comprising:
a charge pump generating a high voltage in response to a pumping clock signal;
a charge/discharge circuit responsive to the pumping clock signal and charging the high voltage to generate an output voltage;
a comparator for comparing the output voltage with a reference voltage to generate a comparison result; and
a clock modification circuit adjusting a pumping slope of the charge pump in relation to the comparison result, wherein the clock modification circuit reduces the pumping slope when the high voltage reaches a target voltage level.
11. The flash memory device of claim 10 , wherein the clock modification circuit reduces the pumping slope of the charge pump by at least one of changing a pulse width for the pumping clock signal, adjusting a frequency of the pumping clock signal, or adjusting an amplitude of the pumping clock signal.
12. The flash memory device of claim 11 , wherein the clock modification circuit reduces the pumping slope of the charge pump in relation to a first and second phase of the pumping clock signal.
13. The flash memory device of claim 10 , wherein the clock modification circuit comprises:
a first inverter inverting a clock signal;
a control circuit responsive to the comparison result and adjusting the speed with which the clock signal applied to the first inverter is inverted; and
a second inverter inverting the output of the first inverter to generate the pumping clock signal.
14. The flash memory device of claim 10 , wherein the clock modification circuit reduces the pumping slope by changing a driving capacitance value associated with the charge pump.
15. The flash memory device of claim 14 , wherein the clock modification circuit comprises:
a plurality of capacitors and a corresponding plurality of switches,
wherein each one of the plurality of capacitors is selectively connected to a corresponding capacitor associated with the charge pump through a switching operation applied to the plurality of switches.
16. The flash memory device of claim 10 , wherein the charge/discharge circuit comprises:
a first charge/discharge circuit charging the high voltage received from the charge pump in response to a first phase of the pumping clock signal and generating the output voltage in response to a second phase of the pumping clock signal; and
a second charge/discharge circuit supplying the output voltage from the first charge/discharge circuit to the comparator in response to the second phase of the pumping clock signal.
17. The flash memory device of claim 16 , wherein the first charge/discharge circuit comprises:
a first high voltage switch outputting the high voltage in response to the first phase of the pumping clock signal;
a first capacitor charging the high voltage received from the first high voltage switch; and
a second high voltage switch outputting a voltage charged in the first capacitor as the output voltage in response to the second phase of the pumping clock signal.
18. The flash memory device of claim 17 , wherein the second charge/discharge circuit includes:
a second capacitor outputting a voltage from the second high voltage switch to the comparator; and
a discharge switch discharging a charged voltage in the second capacitor to ground in response to the first phase of the pumping clock signal, during a charging period of the first capacitor.