Programming pulse ramp control circuit
AssigneeProgrammable Microelectronics Corporation
InventorsVikram Kowshik, Andy Teng-Feng Yu
Life of this patent
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Abstract
A pulse ramp control circuit allows for the program voltage applied to the control gate of a memory cell to be ramped from a low voltage to a high voltage in a precise manner. The ramp rate of this program voltage is primarily determined by a single capacitor and the bias current provided thereto. By providing a ramped program voltage to the memory array during programming operations, present embodiments effectively cover the entire distribution of program voltage v. program current for the memory cells to be programmed, thereby minimizing over-program and under-program conditions without reducing program time.
Claims11
A circuit for providing a ramped programming voltage to an associated memory array using a programming voltage line, said circuit comprising:
- a regulated voltage line having a first voltage thereon;
- a capacitor having a first plate connected to said programming voltage line and having a second plate connected to a node;
- an adjustable current source connected between said regulated voltage line and said first plate of said capacitor and coupled to receive a bias level, wherein said adjustable current source provides a charging current, the magnitude of which is influenced by said bias level, to said capacitor, thereby charging said programming voltage line to said regulated voltage line;
- and
- a control circuit coupled between said programming voltage line and ground potential and having a control terminal connected to said node, said control circuit shunting current from said capacitor when the charging rate of said capacitor increases beyond a predetermined amount.
A method of programming a plurality of non-volatile memory cells, said method comprising:
- (a) providing to said memory cells a first program voltage which ramps from a first voltage to a second voltage to program said memory cells, said second voltage being greater than said first voltage;
- (b) identifying those ones of said memory cells which were not properly programmed;
- and
- (c) providing to those ones of said memory cells identified in step (b) a second program voltage which ramps from said second voltage to a third voltage, said third voltage being greater than said second voltage.
Dependencies are inferred from the claim text.