Reference cells for TCCT based memory cells
View Patent ↗A reference cell produces a reference current that is about half of the current produced by a memory cell. The reference cell is essentially the same as the memory cell with an additional current reduction device that can be a transistor. Adjusting a reference voltage applied to the transistor allows the reference current to be varied. A control circuit to produce the reference voltage includes dedicated memory and reference cells and a feedback circuit that compares the two cells' currents. The feedback circuit applies the reference voltage to the reference cell of the control circuit and adjusts the reference voltage until the current from the reference cell is about half of the current from the memory cell. The reference voltage is then applied to other reference cells in a memory array.
1. A memory array comprising:
a memory cell having a state and configured to generate a first current on a first bit line;
a circuit configured to generate a reference voltage;
a reference cell configured to receive the reference voltage and to generate a second current on a second bit line;
means for determining the state of the memory cell by comparing the first current to the second current; and
first and second word lines;
wherein the memory cell is a TCCT based memory cell including
a first NDR device disposed adjacent to the second word line, and
a first pass transistor with a gate coupled to the first word line.
2. A memory array comprising:
a memory cell having a state and configured to generate a first current on a first bit line;
a circuit configured to generate a reference voltage;
a reference cell configured to receive the reference voltage and to generate a second current on a second bit line; and
means for determining the state of the memory cell by comparing the first current to the second current;
wherein the reference cell includes
an NDR device disposed adjacent to the second word line, and
a pass transistor having a gate with the reference voltage applied thereto.
3. The memory array of claim 1 wherein the means for determining a state of the TCCT based memory cell is a sense amplifier.
4. A memory array comprising:
a first bit line;
a second bit line;
a first word line;
a second word line;
a TCCT based memory cell including
a first NDR device disposed adjacent to the second word line and having
a first end having a first voltage applied thereto, and
a second end;
a first pass transistor having
a source coupled to the second end of the first NDR device,
a drain coupled to the first bit line, and
a gate coupled to the first word line; and
a reference cell including
a second NDR device disposed adjacent to the second word line and having
a first end having the first voltage applied thereto, and
a second end;
a second pass transistor having
a source coupled to the second end of the second NDR device,
a drain, and
a gate coupled to the first word line;
a current reduction element coupled between the second bit line and the drain of the second pass transistor; and
means for determining a state of the TCCT based memory cell by comparing a first current on the first bit line and a second current on the second bit line.
5. The memory array of claim 4 wherein the means for determining a state of the TCCT based memory cell is a sense amplifier.
6. The memory array of claim 4 further including a circuit to generate a reference voltage to control the second current.
7. The memory array of claim 6 wherein the reference voltage is applied to the current reduction element.
8. The memory array of claim 7 wherein the current reduction element is a third pass transistor.
9. A memory device, comprising:
at least one memory array including
at least one TCCT based memory cell;
at least one reference cell; and
a sense amplifier configured to
receive a memory cell current produced by the at least one TCCT based memory cell,
receive a reference cell current produced by the at least one reference cell, and
compare the memory cell current with the reference cell current to determine a state of the at least one TCCT based memory cell.