Sense Amplifier for Flash Memory
First Claim
1. A sense amplifier for sensing data stored in a selected memory cell of a flash memory array, comprising:
- a differential amplifier;
a reference cell current branch comprising a reference cell, a first drain bias section coupled to the reference cell, and a first load section coupled to the first drain bias section and to a first input of the differential amplifier;
a main cell current branch comprising a selected memory cell, a second drain bias section coupled to the selected memory cell, and a second load section coupled to the second drain bias section and to a second input of the differential amplifier; and
a boost circuit comprising a pull-up section coupled to the second input of the differential amplifier and a pull-down section coupled to the selected memory cell.
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Accused Products
Abstract
A sense amplifier has a reference cell current branch in which a reference cell determines a reference cell current, a column load converts the reference cell current to a reference voltage, and a feedback circuit to maintain the reference cell drain voltage. The sense amplifier also has a main cell current branch in which a main cell operationally selected from an array of flash memory cells determines a main cell current, a column load converts the main cell current to a main voltage, and a feedback circuit to maintain the main cell drain voltage. A differential amplifier compares the reference voltage with the main voltage and furnishes a logical level at its output depending on the relative values. A boost circuit has a pull up section coupled across the column load and a pull down section coupled across the main cell for accelerating the logical zero sensing time.
26 Citations
9 Claims
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1. A sense amplifier for sensing data stored in a selected memory cell of a flash memory array, comprising:
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a differential amplifier; a reference cell current branch comprising a reference cell, a first drain bias section coupled to the reference cell, and a first load section coupled to the first drain bias section and to a first input of the differential amplifier; a main cell current branch comprising a selected memory cell, a second drain bias section coupled to the selected memory cell, and a second load section coupled to the second drain bias section and to a second input of the differential amplifier; and a boost circuit comprising a pull-up section coupled to the second input of the differential amplifier and a pull-down section coupled to the selected memory cell. - View Dependent Claims (2, 3, 4, 5)
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6. A method of operating a sense amplifier for reading data stored in a selected memory cell of a flash memory array, comprising:
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activating a reference cell current branch comprising a reference cell, a first drain bias section coupled to the reference cell, and a first load section coupled to the first drain bias section and to a first input of the differential amplifier, wherein a reference voltage is established across the first load section; activating a main cell current branch comprising a selected memory cell, a second drain bias section coupled to the selected memory cell, and a second load section coupled to the second drain bias section and to a second input of the differential amplifier, wherein a sense voltage dependent on the data stored in the selected memory cell is established across the second load section; activating a boost circuit comprising a pull-up section coupled to the second input of the differential amplifier and a pull-down section coupled to the selected memory cell; applying the reference voltage to a first input of a differential amplifier, and the sense voltage to a second input of the differential amplifier; and providing a digital output level from the differential amplifier in accordance with a difference between the reference voltage on the first input of the differential amplifier, and the sense voltage on the first input of the differential amplifier. - View Dependent Claims (7, 8)
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9. A sense amplifier for sensing data stored in a selected memory cell of a flash memory array, comprising:
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a differential amplifier; a VCC voltage node; a VSS voltage node; a reference cell current branch activation signal node; a first cell select NMOS transistor; a second cell select NMOS transistor; a reference cell floating gate MOSFET transistor; a first PMOS transistor switch having a source coupled to the Vcc voltage node, a gate coupled to the reference cell current branch activation signal node, and a drain; a first NMOS transistor load having a drain coupled to the drain of the first PMOS switching transistor, a source coupled to a plus input of the differential amplifier, and a gate coupled to the VCC voltage node; a first NMOS transistor variable conductor having a drain coupled to the source of the first NMOS transistor load, a source coupled to the reference cell floating gate MOSFET transistor through the first and second cell select NMOS transistors, and a gate; a first NMOS transistor feedback element having a drain coupled to the gate of the first NMOS transistor variable conductor, a source coupled to the VSS voltage node, and a gate coupled to the source of the first NMOS transistor variable conductor; a second PMOS transistor switch having a source coupled to the VCC voltage node, a gate coupled to the reference cell activation signal node, and a drain; a first PMOS transistor load having a source coupled to the drain of the first PMOS switching transistor, a drain coupled to the drain of the first NMOS transistor feedback element, and a gate coupled to the drain of the first PMOS transistor load; a main cell current branch activation signal node; a third cell select NMOS transistor; a fourth cell select NMOS transistor; a main cell floating gate MOSFET transistor selected from an array of floating gate MOSFET transistors by the third and fourth cell select NMOS transistors; a third PMOS transistor switch having a source coupled to the VCC voltage node, a gate coupled to the main cell current branch activation signal node, and a drain; a second NMOS transistor load having a drain coupled to the drain of the second PMOS switching transistor, a source coupled to a minus input of the differential amplifier, and a gate coupled to the VCC voltage node; a second NMOS transistor variable conductor having a drain coupled to the source of the second NMOS transistor load, a source coupled to the main cell floating gate MOSFET transistor through the third and fourth cell select NMOS transistors, and a gate; a second NMOS transistor feedback element having a drain coupled to the gate of the second NMOS transistor variable conductor, a source coupled to the VSS voltage node, and a gate coupled to the source of the second NMOS transistor variable conductor; a fourth PMOS transistor switch having a source coupled to the VCC voltage node, a gate coupled to the main cell current branch activation signal node, and a drain; a second PMOS transistor load having a source coupled to the drain of the second PMOS switching transistor, a drain coupled to the drain of the second NMOS transistor feedback element, and a gate coupled to the drain of the second PMOS transistor load; a boost circuit activation signal node; a fifth PMOS transistor switch having a source coupled to the VCC voltage node, a gate coupled to the boost circuit activation signal node, and a drain; a NMOS pull up transistor having a drain coupled to the drain of the fifth PMOS transistor switch, a source coupled to the source of the second NMOS transistor load, and a gate coupled to the VCC voltage node; a boost circuit bias voltage node; and a NMOS pull down transistor having a source coupled to the VSS voltage node, a drain coupled to the source of the second NMOS transistor load, and a gate coupled to the boost circuit bias voltage node.
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Specification