Dual rail single-ended read data paths for static random access memories
Single-ended read circuits for SRAM devices are disclosed for high performance sub-micron designs. One embodiment is an SRAM device that includes a memory cell array and a bit line traversing the memory cell array for reading data from memory cells of the memory cell array. A read circuit coupled to the bit line translates data stored in a memory cell from a cell voltage of the memory cells to a peripheral voltage of an output of the SRAM device while bypassing a level shifter in the read data path.
1. A Static Random Access Memory (SRAM) device, comprising:
a memory cell array;
a bit line traversing the memory cell array for reading data from memory cells of the memory cell array;
a read circuit coupled to the bit line for translating data stored in a memory cell from a cell voltage of the memory cells to a peripheral voltage of an output of the SRAM device, wherein the cell voltage and the peripheral voltage share a common ground, the read circuit comprising:
a data path circuit configured to toggle a first internal signal between a logical zero of the peripheral voltage and a logical one of the peripheral voltage based on read data on the bit line and a second internal signal, and to toggle a third internal signal between a logical zero of the cell voltage and a logical one of the cell voltage based on an enable signal and the read data on the bit line;
a level shifter circuit configured to toggle the second internal signal between a logical zero of the peripheral voltage and a logical one of the peripheral voltage based on the third internal signal and a reset signal; and
an output driver circuit configured to toggle the output of the SRAM device between a logical zero of the peripheral voltage and a logical one of the peripheral voltage based on the first internal signal.
2. The SRAM device of claim 1 wherein the data path circuit comprises:
a first P-channel Field Effect Transistor (FET) having a source terminal coupled to the peripheral voltage, a gate terminal coupled to the bit line, and a drain terminal;
a second P-channel FET having a source terminal coupled to the drain terminal of the first FET, a gate terminal coupled to the second internal signal, and a drain terminal coupled to the first internal signal; and
a third N-channel FET having a drain terminal coupled to the first internal signal, a gate terminal coupled to the bit line, and a source terminal coupled to the common ground.
3. The SRAM device of claim 2 wherein the data path circuit further comprises:
an inverter having a supply terminal coupled to the cell voltage, a ground terminal coupled to the common ground, an input coupled to the bit line, and an output terminal; and
a NAND gate having a supply terminal coupled to the cell voltage, a ground terminal coupled to the common ground, a first input terminal coupled to the output terminal of the inverter, a second input terminal coupled to the enable signal, and an output terminal coupled to the third internal signal.
4. The SRAM device of claim 3 wherein the data path circuit further comprises:
a fourth N-channel FET having a drain terminal coupled to the bit line, a gate terminal coupled to a compliment of the enable signal, and a source terminal coupled to the common ground.
5. The SRAM device of claim 1 wherein the output circuit comprises:
a first P-channel Field Effect Transistor (FET) having a source terminal coupled to the peripheral voltage, a gate terminal coupled to the first internal signal, and a drain terminal coupled to the output of the SRAM device; and
a second N-channel FET having a drain terminal coupled to the output of the SRAM device, a gate terminal coupled to the first internal signal, and a source terminal coupled to the common ground.
6. The SRAM device of claim 1 wherein the level shifter circuit comprises:
a first P-channel Field Effect Transistor (FET) having a source terminal coupled to the peripheral voltage, a gate terminal coupled to the second internal signal, and a drain terminal;
a second P-channel FET having a source terminal coupled to the drain terminal of the first FET, a gate terminal coupled to the third internal signal, and a drain terminal;
a third N-channel FET having a drain terminal coupled to the drain terminal of the second FET, a gate terminal coupled to the third internal signal, and a source terminal coupled to the common ground;
a fourth N-channel FET having a drain terminal coupled to the drain terminal of the third FET, a gate terminal coupled to the second internal signal, and a source terminal coupled to the common ground;
a fifth P-channel FET having a source terminal coupled to the peripheral voltage, a gate terminal, and a drain terminal;
a sixth P-channel FET having a source terminal coupled to the drain terminal of the fifth FET, a gate terminal coupled to the drain terminal of the fourth FET, and a drain terminal coupled to the second internal signal;
a seventh N-channel FET having a drain terminal coupled to the second internal signal, a gate terminal coupled to the reset signal, and a source terminal;
an eighth N-channel FET having a drain terminal coupled to the source terminal of the seventh FET, a gate terminal coupled to the gate terminal of the fifth FET, and a source terminal coupled to the common ground;
a ninth P-channel FET having a source terminal coupled to the peripheral voltage, a gate terminal coupled to the reset signal, and a drain terminal coupled to the second internal signal; and
an inverter having a supply terminal coupled to the cell voltage, a ground terminal coupled to the common ground, an input terminal coupled to the third internal signal, and an output terminal coupled to the gate terminal of the eighth FET.
7. A Static Random Access Memory (SRAM) device, comprising:
a memory cell array;
a bit line traversing the memory cell array for reading data from memory cells of the memory cell array;
a read circuit coupled to the bit line for translating data stored in a memory cell from a cell voltage of the memory cells to a peripheral voltage of an output of the SRAM device, wherein the cell voltage and the peripheral voltage share a common ground, the read circuit comprising:
a data path circuit configured to toggle a first internal signal between a logical zero of the peripheral voltage and a logical one of the peripheral voltage based on read data on the bit line and a second internal signal, and to set the bit line to a logical zero based on the second internal signal and a compliment of an enable signal;
a level shifter circuit configured to toggle the second internal signal between a logical zero of the peripheral voltage and a logical one of the peripheral voltage based on the enable signal and a reset signal; and
an output driver circuit configured to toggle the output of the SRAM device between a logical zero of the peripheral voltage and a logical one of the peripheral voltage based on the first internal signal.
8. The SRAM device of claim 7 wherein the data path circuit comprises:
a first P-channel Field Effect Transistor (FET) having a source terminal coupled to the peripheral voltage, a gate terminal coupled to the bit line, and a drain terminal;
a second P-channel FET having a source terminal coupled to the drain terminal of the first FET, a gate terminal coupled to the second internal signal, and a drain terminal coupled to the first internal signal; and
a third N-channel FET having a drain terminal coupled to the first internal signal, a gate terminal coupled to the bit line, and a source terminal coupled to the common ground.
9. The SRAM device of claim 8 wherein the data path circuit further comprises:
a third N-channel FET having a drain terminal coupled to the bit line, a gate terminal coupled to the second internal signal, and a source terminal; and
a fourth N-channel FET having a drain terminal coupled to the source terminal of the third FET, a gate terminal coupled the compliment of the enable signal, and a source terminal coupled to the common ground.
10. The SRAM device of claim 7 wherein the level shifter circuit comprises:
a first P-channel Field Effect Transistor (FET) having a source terminal coupled to the peripheral voltage, a gate terminal coupled to the reset signal, and a drain terminal coupled to the second internal signal;
a second N-channel FET having a drain terminal coupled to the second internal signal, a gate terminal coupled to the reset signal, and a source terminal;
a third N-channel FET having a drain terminal coupled to the source terminal of the second FET, a gate terminal coupled to the enable signal, and a source terminal coupled to the common ground;
a fourth P-channel FET having a source terminal coupled to the peripheral voltage, a gate terminal coupled to the enable signal, and a drain terminal;
a fifth P-channel FET having a source terminal coupled to the drain terminal of the fourth FET, a gate terminal, and a drain terminal coupled to the second internal signal; and
an inverter having a supply terminal coupled to the peripheral voltage, a ground terminal coupled to the common ground, an input terminal coupled to the second internal signal, and an output terminal coupled to the gate terminal of the fifth FET.
11. The SRAM device of claim 7 wherein the output circuit comprises:
a first P-channel Field Effect Transistor (FET) having a source terminal coupled to the peripheral voltage, a gate terminal coupled to the first internal signal, and a drain terminal coupled to the output of the SRAM device; and
a second N-channel FET having a drain terminal coupled to the output of the SRAM device, a gate terminal coupled to the first internal signal, and a source terminal coupled to the common ground.