Implementing logic function and generating analog signals using NOR memory strings
NOR memory strings may be used for implementations of logic functions involving many Boolean variables, or to generate analog signals whose magnitudes are each representative of the bit values of many Boolean variables. The advantage of using NOR memory strings in these manners is that the logic function or analog signal generation may be accomplished within one simultaneous read operation on the NOR memory strings.
1. A method for generating an analog signal representative of an input Boolean string, comprising:
providing a plurality of memory cells wherein (i) the memory cells share a common drain region and a common source region in a NOR memory string configuration, wherein one or both of the common source region and the common drain region being provided as a substantially uniform strip of conductive semiconductor material, and (ii) the memory cells are separated from each other substantially uniformly along the substantially uniform strip of conductive semiconductor material;
associating each bit of the Boolean string to a selected one of the memory cells;
programming each selected memory cell to a conductive state or a non-conductive state according to the value of the associated bit in the Boolean string; and
reading the selected memory cells simultaneously to obtain a current flowing in the substantially uniform strip of semiconductor material and providing that current as the analog signal, wherein either the common drain region or the common source region, but not both, is provided a lower resistance relative to the other, such that the resulting current for any of the selected memory cells is also determined in part by where along the substantially uniform strip of semiconductor material is that memory cell located.
2. The method of claim 1 , wherein the lower resistance is provided by a metallic layer provided adjacent to the common source region or the common drain region.
3. The method of claim 1 , wherein the analog signal is representative of a weighted sum, with each weight determined by where a corresponding one of the selected memory cells is located along the substantially uniform strip of semiconductor material.
4. The method of claim 1 , wherein the selected memory cells implement a neuron in a neural network.
5. The method of claim 1 , wherein the memory cells are organized into a plurality of 3-dimensional arrays of memory cells provided above a semiconductor substrate.
6. The method of claim 5 , wherein the 3-dimensional arrays are organized into tiles.
7. The method of claim 6 , wherein the memory cells in a selected group of tiles are configured to be non-volatile.
8. The method of claim 6 , wherein the memory cells in a selected group of tiles are configured to be quasi-volatile.
9. The method of claim 1 , wherein the analog signal is provided as an input signal to analog circuitry.
10. The method of claim 1 , wherein the analog circuitry is provided in the semiconductor substrate or in an accompanying integrated circuit.