Programmable cell
View Patent ↗A device having an OTP memory is disclosed. A program state of the OTP device is stored at a fuse that is connected in series between a first node and a latch. During a program mode, the first node is electrically connected to a program voltage. During a read mode, the first node is electrically connected to ground, whereby a first divided voltage is generated at a first node of the latch.
1. A method comprising:
receiving a program voltage at a first node during a program mode;
receiving a read voltage at the first node during a read mode, wherein the read voltage is different than the program voltage; and
during the read mode, dividing a first voltage between the first node and a first current electrode of a first transistor of a bit cell to generate a first divided voltage at a second node, wherein the first current electrode and a second current electrode of the first transistor are coupled in series between a voltage reference node and the second node, and a programmable fuse is coupled in series between the first node and the second node.
2. The method of claim 1 further comprising:
latching a first logic value at the second current electrode of the first transistor based upon the first divided voltage.
3. The method of claim 2 further comprising:
during the read mode, dividing a second voltage between the first node and a first current electrode of a second transistor of the bit cell to generate a second divided voltage at a third node, wherein the first current electrode and a second current electrode of the second transistor are coupled in series between the voltage reference node and the third node, and a reference resistance is coupled in series between the first node and the third node.
4. The method of claim 3 further comprising:
latching a second logic value at the second current electrode of the second transistor based upon the second divided voltage, wherein the first logic value and the second logic value are complementary values.
5. The method of claim 4 wherein the second divided voltage is substantially less than a voltage of the second logic value.
6. The method of claim 1 further comprising:
during the read mode, dividing a second voltage between the first node and a first current electrode of a second transistor of the bit cell to generate a second divided voltage at a third node, wherein the first current electrode and a second current electrode of the second transistor are coupled in series between the voltage reference node and the third node, and a reference resistance is coupled in series between the first node and the third node.
7. The method of claim 6 , wherein dividing the first voltage comprises providing a first portion of the first voltage across the first transistor, a second portion of the first voltage across the programmable fuse, and a third portion of the first voltage across a first pass gate, wherein a first current electrode of the first pass gate and a second current electrode of the first pass gate are coupled in series between the second node and a first electrode of the programmable fuse, and wherein a sum of the first portion of the first voltage across the first transistor, the second portion of the first voltage across the programmable fuse, and the third portion of the first voltage across the first pass gate is substantially equal to the first voltage.
8. The method of claim 1 further comprising:
during the read mode, dividing the first voltage to generate a second divided voltage at a third node, wherein a first current electrode and a second current electrode of a second transistor of the bit cell are coupled in series between the third node and the first current electrode of the first transistor, and a reference resistance is coupled in series between the first node and the third node.
9. The method of claim 1 further comprising:
during the program mode, programming the programmable fuse by supplying a program current through the programmable fuse, wherein the program current is approximately proportional to the program voltage.
10. The method of claim 9 , wherein programming further comprises electrically isolating the second node from the first node when supplying the program current through the programmable fuse.
11. The method of claim 10 , wherein electrically isolating comprises electrically isolating the second node from the first node through a pass gate.
12. The method of claim 11 , wherein a transistor of the pass gate comprises a first maximum gate voltage that is greater than a second maximum gate voltage of a second transistor of the bit cell, wherein the second transistor and the transistor of the pass gate are of a common conductivity type.
13. The method of claim 1 wherein the read voltage is approximately equal to ground.
14. A device comprising:
a bit cell comprising:
a latching device comprising a first transistor comprising a first current electrode, a second current electrode, and a control electrode, wherein the latching device is operable to latch data at the second current electrode;
a pass gate comprising a first current electrode coupled to the second current electrode of the first transistor, a second current electrode, and a control electrode;
a programmable fuse comprising a first electrode coupled to the second electrode of the pass gate, and a second electrode;
a second transistor comprising a first electrode coupled to a voltage reference node, a second electrode coupled to the first electrode of the programmable fuse, and a control electrode, wherein the second transistor is enabled to program the programmable fuse;
a first control module comprising a first output coupled to the second electrode of the programmable fuse to provide a first voltage relative to a voltage at the voltage reference node when programming the programmable fuse, and to provide a second voltage relative to the voltage at the voltage reference node when reading a state of the fuse.
15. The device of claim 14 further comprising:
a second control module comprising a first output coupled to the control electrode of the pass gate to activate the pass gate when determining a program state of the programmable fuse, and to deactivate the pass gate when programming the programmable fuse.
16. The device of claim 14 , wherein:
the latching device comprises a second transistor comprising a first electrode coupled to the second electrode of the first transistor, wherein the second transistor and a transistor of the pass gate have a common conductivity type, and a gate dielectric of the transistor of the pass gate is substantially thicker than a gate dielectric of the second transistor.
17. The device of claim 14 , wherein
the bit cell further comprises:
a second pass gate comprising a first current electrode coupled to the control gate of the first transistor, a second current electrode, and a control gate coupled to the control gate of the first pass gate; and
a resistor comprising a first electrode coupled to the second electrode of the second pass gate, and a second electrode.
18. The device of claim 17 , wherein the second electrode of the resistor is further coupled to the second electrode of the programmable fuse.
19. The device of claim 14 , wherein the latching device further comprises:
a third transistor comprising a first current electrode coupled to the second current electrode of the first transistor, a second electrode, and a control electrode coupled to the control electrode of the first transistor; and
a fourth transistor comprising a first current electrode coupled to second electrode of the third transistor, a second electrode, and a control electrode coupled to receive a signal to latch the data at the second current electrode of the first transistor.
20. The device of claim 14 , wherein the bit cell is one of a plurality of bit cells of a memory array, each bit cell of the memory array comprising a corresponding programmable fuse.