Equivalent fuse circuit for a one-time programmable read-only memory array
Technologies are provided for measuring a programming current (PC) for a memory cell (MC) of a one-time programmable read-only memory array. The MC includes a fuse equivalent circuit (FEC) that includes a first current path (CP) having a first node, a second CP having a fuse of the memory cell and a second node, and a third CP. The PC is split into a first current, a second current and a third current that flow over the first CP, the second CP, and the third CP, respectively. A first voltage applied along the first path is divided to generate a second voltage at the first node, and an output voltage generated by an operational amplifier controls the second current to maintain a third voltage at the second node at substantially the same value as the second voltage so that the second current has a sufficiently low value and does not burn the fuse.
1. A one-time programmable read-only memory array, comprising:
a memory cell, comprising:
a first transistor; and
a fuse equivalent circuit configured to receive a programming current and configured to output the programming current to the first transistor, the fuse equivalent circuit comprising:
a voltage divider configured to divide a first voltage to generate a second voltage;
an operational amplifier comprising: a first input configured to receive a third voltage, a second input coupled to the voltage divider and being configured to receive the second voltage, and an output that is configured to generate an output voltage;
a current mirror configured to receive the output voltage and configured to generate a first current; and
a fuse coupled to the first transistor at a node and the voltage divider at the node, the fuse being configured to receive the first current from the current mirror, wherein the output voltage generated by the operational amplifier controls the first current to maintain the third voltage at substantially the same value as the second voltage.
2. A one-time programmable read-only memory array according to claim 1 , wherein the first current generated by the current mirror has a sufficiently low value such that the fuse does not burn when the first current flows through the fuse.
3. A one-time programmable read-only memory array according to claim 1 , wherein the node is a first node, and wherein the current mirror and the fuse are coupled to a second node that is coupled to the first input of the operational amplifier, and wherein the voltage divider is coupled to the current mirror.
4. A one-time programmable read-only memory array according to claim 3 , wherein the voltage divider comprises:
a first resistor coupled to a second resistor at the first node, wherein the voltage divider divides the first voltage to generate the second voltage at the first node that is less than the first voltage, wherein a first resistance value of the first resistor is greater than a second resistance value of the second resistor.
5. A one-time programmable read-only memory array according to claim 1 , wherein the current mirror receives the output voltage generated by the output of the operational amplifier and generates the first current, and wherein the current mirror comprises:
a first P-channel MOSFET comprising a first gate having a first width-to-length value, and being configured to generate the first current; and
a second P-channel MOSFET comprising a second gate having a second width-to-length value, and being configured to generate a second current,
wherein the output voltage generated by the operational amplifier is applied to the first and second gates of the first P-channel MOSFET and the second P-channel MOSFET to control the first current generated by the first P-channel MOSFET to maintain the third voltage at substantially the same value as the second voltage.
6. A one-time programmable read-only memory array according to claim 5 , wherein a ratio of the first current to the second current is determined based on a ratio of the first gate width-to-length value of the first P-channel MOSFET to the second gate width-to-length value of the second P-channel MOSFET.
7. A one-time programmable read-only memory array according to claim 6 , wherein the first current generated by the first P-channel MOSFET is substantially less than the second current generated by the second P-channel MOSFET such that the first current that flows through the fuse is sufficiently small enough to prevent the fuse from burning.
8. A one-time programmable read-only memory array according to claim 6 , wherein the second gate width-to-length value of the second P-channel MOSFET is greater than the first gate width-to-length value of the first P-channel MOSFET.
9. A one-time programmable read-only memory array according to claim 1 , further comprising:
a second memory cell comprising an unburned fuse having an impedance, wherein an impedance of the fuse equivalent circuit is the substantially same as the impedance of the unburned fuse.