High frequency pseudo dual port memory
A pseudo dual port (PDP) memory is disclosed having a write driver that selectively precharges only one of a bit line and a complement bit line in a bit line pair responsive to a bit value to be written into an accessed bitcell while discharging a remaining one of the bit line and the complement bit line. In this fashion, the cleanup time between a read operation and a write operation during a read/write clock cycle is advantageously reduced.
1. A method for accessing a bitcell of a pseudo dual port (PDP) memory, comprising:
asserting a word line voltage during a read portion of a memory clock cycle to couple a bitcell to a bit line and a complement bit line for a bit line pair;
de-asserting the word line voltage for a write precharge portion of the memory clock cycle; and
during the write precharge portion of the memory clock cycle, selectively precharging to a power supply voltage VDD only one of the bit line and the complement bit line in the bit line pair while discharging a remaining one of the bit line and the complement bit line, the selective precharging and discharging being responsive to a bit value to be written into the bitcell;
coupling the selectively precharged and discharged bit line pair to the bitcell to write the bit value into the bitcell during a read/write clock cycle.
2. The method of claim 1 , wherein the bit line pair is part of a write multiplexed group comprising the bit line pair and additional bit line pairs, the method further comprising precharging the additional bit line pairs to the power supply voltage VDD during the selective precharging of the bit line pair.
3. The method of claim 2 , wherein the selective precharging of the bit line pair is further responsive to assertion of a write multiplex signal corresponding to the bit line pair.
4. The method of claim 2 , wherein the precharging of the additional bit line pairs is responsive to a de-assertion of a write multiplex signal for each of the additional bit line pairs.
5. The method of claim 3 , wherein the selective precharging of the bit line pair comprises switching on a first data precharge path to the one of the bit line and the complement bit line responsive to the bit value, and wherein the discharging comprises switching off a second data precharge path to the remaining one of bit line and the complement bit line responsive to the bit value.
6. The method of claim 5 , further comprising switching on a first head switch for the first data precharge path and switching on a second head switch for the second data precharge path.
7. The method of claim 1 , further comprising:
reading a stored value from the bitcell during the read portion of the memory cycle.
8. The method of claim 7 , wherein reading the stored value from the bitcell during the read portion of the memory cycle occurs after a read precharge operation of precharging both the bit line and the complement bit line in the bit line pair.
9. A pseudo dual port (PDP) memory, comprising:
a bit line and a complement bit line in a first bit line pair;
a read pre-charge circuit configured to precharge the bit line and the complement bit line during a read precharge portion of a memory clock cycle; and
a write driver configured to selective precharge only one of the bit line and the complement bit line to a power supply voltage VDD responsive to a bit value to be written into a bitcell during a write portion of the memory clock cycle, the write driver being further configured to discharge a remaining one of the bit line and the complement bit line during the selective precharge.
10. The PDP memory of claim 9 , further comprising a write multiplexed group of bit line pairs including the first bit line pair and additional bit line pairs, and wherein the write driver is further configured to precharge the additional bit line pairs such that a bit line and a complement bit line in each of the additional bit line pairs is precharged to VDD during the selective precharging of the first bit line pair.
11. The PDP memory of claim 10 , wherein the write driver is further configured to receive a write multiplexing signal and to selectively precharge the first bit line pair responsive to the write multiplexing signal.
12. The PDP memory of claim 11 , further comprising:
a first data precharge path and a first write multiplexing precharge path coupled in parallel to the bit line; and
a second data precharge path and a second write multiplexing precharge path coupled in parallel to the complement bit line.
13. The PDP memory of claim 12 , wherein the first data precharge path comprises a data transistor having a gate configured to receive a complement of the bit value, and wherein the second data precharge path comprises a data transistor having a gate configured to receive the bit value.
14. The PDP memory of claim 13 , wherein the first write multiplexing precharge path and the second write multiplexing precharge path each comprises a write multiplexing transistor having a gate configured to receive the write multiplexing signal.
15. The PDP memory of claim 12 , wherein the first data precharge path and the first write multiplexing path couple in parallel to a power supply node through a first head switch, and wherein the second data precharge path and the second write multiplexing path couple in parallel to a power supply node through a second head switch.
16. The PDP memory of claim 9 , further comprising a logic gate configured to assert a write precharge signal during the selective precharging of the first bit line pair, and wherein the first head switch and the second head switch are configured to switch on responsive to the assertion of the write precharge signal.
17. The PDP memory of claim 16 , wherein the logic gate comprises a NAND gate.
18. A pseudo dual port (PDP) memory, comprising:
a bit line and a complement bit line in a first bit line pair;
a read pre-charge circuit configured to precharge the bit line and the complement bit line during a read precharge portion of a memory clock cycle; and
means for selectively precharging, during a write precharge portion of the memory clock cycle, only one of the bit line and the complement bit line to a power supply voltage VDD responsive to a bit value to be written into a bitcell and for discharging a remaining one of the bit line and the complement bit line during the selective precharge.
19. The PDP memory of claim 18 , further comprising:
a write multiplexing group including the first bit line pair and additional bit line pairs; and
means for precharging the additional bit line pairs such that a bit line and a complement bit line in each of the additional bit line pairs is precharged to the power supply voltage VDD during the selective precharging of the first bit line pair.