Drain voltage pumping circuit

Details Drain voltage pumping circuit Drain voltage pumping circuit

1999-10-27

2001-03-27

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

06208198

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drain voltage pumping circuit, and more particularly to a drain voltage pumping circuit to reduce current dissipation in program operation by detecting the number of bits for programming at the time of program operation on a flash memory cell and by allowing drain pumping voltage control depending on the number of cells for programming.
2. Description of the Prior Art
Generally, memory cells in a flash memory are by applying high voltage, for example, 8 through 9V to a control gate and the supply voltage, for example, 4 through 5V to a drain electrode. For supplying such high voltage or supply voltage, drain voltage pumping circuits are used.
FIG. 1
is a typical drain voltage pumping circuit. A drain voltage pumping unit
2
for programming memory cells in a memory cell array
1
comprises a ring oscillator
3
and a pumping unit
4
.
Operation of a typical drain voltage circuit constituted as described above will be explained with reference to FIG.
2
A and FIG.
2
B.
FIG. 2A
is a detailed circuit of the ring oscillator. The ring oscillator comprises: a NAND gate
5
to use enable signals En as input; a first delay unit
6
to delay output of the NAND gate
5
; a first inverter I
1
to inverse output of the first delay unit
6
; a second delay unit
7
to delay output of the first inverter I
1
; a second inverter I
2
to invent output of the second delay unit
7
and provide the output to a remain input terminal of the NAND gate
5
; a third inverter I
3
for generating a first control signal &phgr;
1
by inversing output of the second inverter I
2
; and a fourth inverter I
4
for generating a second control signal &phgr;
2
by inversing output of the third inverter I
3
.
FIG. 2B
is a detailed circuit of pumping unit. The pumping unit comprises: a first NMOS transistor and a second NMOS transistor N
1
and N
2
connected in parallel between the supply power Vcc and the first node K
1
; a first capacitor and a second capacitor C
1
and C
2
to use first and second control signals &phgr;
1
and &phgr;
2
of the ring oscillator as input; and a third NMOS transistor N
3
connected between the first node K
1
and the output terminal Out.
As described above, a typical drain voltage pumping circuit programmed 8 bits or 16 bits at the same time, using one pumping device, as shown in FIG.
2
B.
For example, if a pumping circuit is constituted for programming when the number of bits for programming is assumed to be 16, excessive power dissipation occurs in programming 8 bits. Also, if a pumping circuit is constituted for programming when the number of bits for programming is assumed to be 8, enough program pumping output can not be obtained since current supply is small in 16 bits programming.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a drain voltage pumping circuit to settle above problems by detecting the number of bits for programming at the time of programming in flash memory cells and adjusting drain pumping voltage depending on the number of cells for programming.
A drain voltage pumping circuit in accordance with the present invention to achieve the object as described above comprises: a detection unit for outputting program control signal by detecting the number of bits for programming before programming memory cells on a memory cell array; and a drain voltage pumping unit for generating a drain voltage according to the program control signals of the detection unit.
Also, a drain voltage pumping circuit comprises: a detection circuit for detecting the number of bits to be programmed of a plurality of bits and for generating a plurality of program control signals according to the number of bits; and a drain voltage pumping unit having a ring oscillator and a pumping circuit, with the ring oscillator generating pulse signals having cycles which are different from each other in respond to the program control signal and the pumping circuit generating a drain voltage according to a pulse signal from the ring oscillator.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.


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