Electronic device and method for operating a memory circuit
View Patent ↗An electronic device includes a memory cell that utilizes a bi-directional low impedance, low voltage drop full pass gate to connect a bit cell to a bit write line during a write phase, and during a read phase the full pass gate can remain off and a high input impedance read port can acquire and transmit the logic state stored by the memory cell to another subsystem. The full pass gate can be implemented by connecting a P type metal semiconductor field effect transistor (PMOS) in parallel with an NMOS device and driving the gates of the transistors with a differential signal. When a write operation requires a current to flow in a first direction, the PMOS device provides a negligible voltage drop, and when the write operation requires current to flow in a second or the opposite direction, the NMOS device can provide a negligible voltage. This bi-directional low voltage drop low loss switch can increase the write margin of the memory cell wherein the high impedance read port can provide increased isolation for the stored value during the read phase increasing the performance of the memory cell.
1. An electronic device comprising:
a full pass gate controllable by a write control line and a complimentary write control line, the full pass gate comprising:
a first semiconductor transistor comprising a first electrode coupled to a first node of the bit cell, a second electrode coupled to a write bit line, and control electrode coupled to the write control line; and
a second semiconductor transistor comprising a first electrode coupled to the first node of the bit cell, a second electrode coupled to the write bit line, and a control electrode coupled to the complementary write control line;
a bit cell operably coupled to the full pass gate comprising a first node configured to receive a signal via the full pass gate and store the signal during a write phase to a write control signal; and
a read control line separate from the write control line, configured to control a read phase wherein the signal is read from the bit cell during the read phase;
and wherein a voltage drop across the first semiconductor transistor is less than one-half of voltage threshold of a transistor of the pass gate when the first semiconductor transistor is forward biased.
2. The device as in claim 1 , wherein the first semiconductor transistor is a P-type transistor and the second semiconductor transistor is an N-type transistor.
3. The device as in claim 1 , wherein a voltage drop across the second semiconductor transistor is substantially zero volts when the second semiconductor transistor is forward biased.
4. The device as in claim 1 , further comprising an inverter having an input coupled to the write control line configured to generate a complementary write signal from a write signal at the write control line.
5. The device as in claim 1 , further comprising a read port coupled between the bit cell and a read bit line, the read port having an input coupled to the first node of the bit cell to acquire a value of the stored bit and an output coupled to the read bit line.
6. The device as in claim 5 , wherein the read port further comprises a first transistor coupled in a series configuration with a second transistor.
7. The device as in claim 1 , further comprising a write line enable logic gate coupled to the write line and configured to enable and disable the write line.
8. The device as in claim 1 , further comprising:
a third semiconductor transistor comprising a first electrode coupled to a second node of the bit cell, a second electrode coupled to a complementary bit line, and a control electrode coupled to the write control line; and
a fourth semiconductor transistor comprising a first electrode coupled to the second node of the bit cell, a second electrode coupled to the complementary bit line, and a control electrode configured to receive a complementary write control signal.
9. The device as in claim 8 , wherein a voltage drop across the third semiconductor transistor is less than 0.6 volts when the third semiconductor transistor is forward biased and a voltage drop across the fourth semiconductor transistor is less than one-half a voltage threshold of a transistor of the pass gate when the fourth semiconductor transistor is forward biased.
10. A method comprising:
controlling a full pass gate of a memory cell during a write phase, the full pass gate configured to provide approximately the same impedance between a write bit line and a bit cell during the write phase for a logic level high signal and a logic level low signal; and
controlling a read port of the memory cell that is independent of the full pass gate during a read phase, the read port configured to relay a signal from the bit cell to a read bit line wherein and the read port provides high impedance isolation between the bit cell and a read bit line.
11. The method of claim 10 , wherein controlling the read port further comprises asserting a read port control signal during a read phase and negating a read port control signal during a write phase.
12. The method of claim 10 , wherein controlling the full pass gate further comprises controlling a first transistor with a write control signal and controlling a second transistor with a complementary write control signal.
13. The method of claim 10 , wherein controlling the first pass gate further comprises activating a write signal wherein the write signal can be activated with a write enable signal.
14. The method of claim 10 , wherein controlling the full pass gate further comprises controlling the full pass gate based on a column select signal.
15. An electronic device comprising:
a first pass gate comprising:
a first transistor comprising a first current electrode at a first location of a first diffusion strip of an integrated circuit, a second current electrode at a second location of the first diffusion strip, and a control gate;
a second transistor comprising a first current electrode at a first location of a second diffusion strip of an integrated circuit, a second current electrode at a second location of the second diffusion strip, and a control gate, wherein the first current electrode is coupled to the first current electrode of the first transistor and the second current electrode is coupled to the second current electrode of the second transistor;
a second pass gate comprising:
a third transistor comprising a first current electrode at a third location of a first diffusion strip of an integrated circuit, a second current electrode at a fourth location of the first diffusion strip, and a control gate;
a fourth transistor comprising a first current electrode at a third location of a second diffusion strip of an integrated circuit, a second current electrode at a fourth location of the second diffusion strip, and a control gate, wherein the first current electrode is coupled to the first current electrode of the third transistor and the second current electrode is coupled to the second current electrode of the third transistor;
a latch comprising:
a fifth transistor comprising first current electrode at the second location of the first diffusion strip, and a second electrode at a fifth location of the first diffusion strip;
a sixth transistor comprising first current electrode at the fifth location of the first diffusion strip, and a second electrode at the third location of the first diffusion strip, wherein the fifth location is between the second location and the third location.
16. The electronic device of claim 15 wherein the second and third locations are between the first and second locations.
17. The electronic device of claim 15 wherein the latch further comprises a voltage reference node coupled to the 5th location of the diffusion strip.