Static semiconductor memory with a dummy call and a write assist operation
View Patent ↗A dummy memory cell for detection of write completion timing is provided as a replica of a memory cell. When assisting a write operation by power supply control and substrate potential control of the memory cell, the timing of ending the write assist operation is determined by a voltage control circuit based on information about the dummy memory cell. For example, the voltage control circuit performs, in a data write operation in the memory cell, the write assist operation of decreasing the voltage of a source power supply allocated to P-channel MOS load transistors using a pull-down transistor. Thereafter, at the time when completion of the data write operation in the dummy memory cell is detected, the voltage control circuit ends the write assist operation and restores the voltage of the source power supply to the original level using a pull-up transistor.
1. A static semiconductor memory, comprising:
a memory cell including a pair of P-channel MOS load transistors, a pair of N-channel MOS transfer transistors, and a pair of N-channel MOS drive transistors;
a dummy memory cell including a pair of P-channel MOS load transistors, a pair of N-channel MOS transfer transistors, and a pair of N-channel MOS drive transistors; and
voltage control circuits selected from the group of the following voltage control circuits consisting of:
a voltage control circuit for decreasing a voltage of a source power supply allocated to the P-channel MOS load transistors of both the memory cell and the dummy memory cell,
a voltage control circuit for increasing a voltage of a source power supply allocated to the N-channel MOS drive transistors of both the memory cell and the dummy memory cell,
a voltage control circuit for increasing a substrate potential of the P-channel MOS load transistors of both the memory cell and the dummy memory cell,
a voltage control circuit for increasing a substrate potential of the N-channel MOS transfer transistors of both the memory cell and the dummy memory cell, and
a voltage control circuit for decreasing a substrate potential of the N-channel MOS drive transistors of both the memory cell and the dummy memory cell, wherein:
in a data write operation for the memory cell,
the voltage increasing or decreasing operation starts as a write assist operation,
a data write operation for the dummy memory cell starts by supplying a dummy selection signal to gates of the pair of N-channel MOS transfer transistors of the dummy memory cell before supplying a selection signal to gates of the pair of N-channel MOS transfer transistors of the memory cell, and
the voltage increasing or decreasing operation as a write assist operation ends after completion of the data write operation for the dummy memory cell is detected.
2. The static semiconductor memory of claim 1 , further comprising another dummy memory cell which includes a pair of P-channel MOS load transistors, a pair of N-channel MOS transfer transistors, and a pair of N-channel MOS drive transistors,
wherein the voltage increasing or decreasing operation ends based on a result of a logical operation of values of memory nodes of the dummy memory cells.
3. The static semiconductor memory of claim 1 , further comprising another memory cell which includes a pair of P-channel MOS load transistors, a pair of N-channel MOS transfer transistors, and a pair of N-channel MOS drive transistors and which shares one word line with the memory cell,
wherein the dummy memory cell is utilized to perform a same voltage increasing or decreasing operation in each of the memory cells.
4. The static semiconductor memory of claim 1 , further comprising another memory cell which includes a pair of P-channel MOS load transistors, a pair of N-channel MOS transfer transistors, and a pair of N-channel MOS drive transistors and which shares a pair of bit lines with the memory cell,
wherein the dummy memory cell is utilized to perform a same voltage increasing or decreasing operation in each of the memory cells.
5. The static semiconductor memory of claim 1 , further comprising any one of:
a voltage increasing transistor which has a gate coupled to a first control signal, a source coupled to a first power supply, and a drain coupled to sources allocated to the N-channel MOS drive transistors of both the memory cell and the dummy memory cell, and
a voltage decreasing transistor which has a gate coupled to a second control signal, a source coupled to a second power supply, and a drain coupled to sources allocated to the P-channel MOS load transistors of both the memory cell and the dummy memory cell,
wherein the first control signal and the second control signal are controlled according to a value of the memory node of the dummy memory cell.