Threshold evaluation of EPROM cells
View Patent ↗Evaluating an embedded EPROM in a host IC device involves using program circuitry to program/unprogram all of the floating-gate cells of the embedded EPROM, then simultaneously transmitting a predetermined test bias voltage to all of the programmed/unprogrammed floating-gate cells, and then evaluating the output terminals of all of the floating-gate cells using a logic (e.g., wired NOR or NAND) circuit, whereby successful operation of all of the embedded EPROM cells causes the wired logic circuit to generate a single positive test result signal, and the failure of one or more of the embedded EPROM cells causes the wired logic circuit to generate a single negative test signal. A reference cell is also evaluated using a bias testing circuit to determine that the reference voltage supplied during normal operation is at an acceptable voltage level.
1. A method for evaluating an embedded EPROM in an integrated circuit, the method comprising:
applying predetermined voltages to a plurality of floating-gate cells of the embedded EPROM, whereby a floating gate of each of said plurality of floating-gate cells is subjected to a predetermined programming/unprogramming potential;
after de-asserting the predetermined voltages, coupling a control gate of each said of said floating-gate cells to a predetermined test bias voltage, and coupling an output terminal of each of said floating-gate cells to a logic circuit, whereby each said of said floating-gate cells transmits an output signal to said logic circuit in response to said predetermined test bias voltage, wherein the logic circuit includes means for generating a single-bit cell test result signal having a first logic value when all of said plurality of floating-gate cells store a predetermined programmed/unprogrammed charge, and for generating said single-bit cell test result signal having a second logic value when one or more of said plurality of floating-gate cells fails to store said predetermined programmed/unprogrammed charge; and
transmitting said single-bit cell test result signal out of said integrated circuit to an external test system.
2. The method according to claim 1 ,
wherein applying said predetermined voltages comprises unprogramming all of said plurality of floating-gate cells, and
wherein coupling said control gate of each of said floating-gate cells to said logic circuit comprises coupling said control gates to a wired NOR cell.
3. The method according to claim 1 ,
wherein applying said predetermined voltages comprises programming all of said plurality of floating-gate cells, and
wherein coupling said control gate of each said of said floating-gate cells to said logic circuit comprises coupling said control gates to a wired NAND cell.
4. The method according to claim 1 , further comprising:
coupling a reference cell to a bias testing circuit and adjusting a system voltage of said integrated circuit such that a bias voltage generated by the reference cell is sequentially compared against a first predetermined reference voltage and a second predetermined reference voltage, wherein the bias testing circuit includes means for generating a single-bit bias test result signal having a first logic value when said bias voltage is greater than said first predetermined reference voltage, for generating said single-bit bias test result signal having a second logic value when said bias voltage is less than said first predetermined reference voltage, for generating said single-bit bias test result signal having the second logic value when said bias voltage is greater than said second predetermined reference voltage, and for generating said single-bit bias test result signal having the first logic value when said bias voltage is less than said second predetermined reference voltage.
5. An integrated circuit comprising:
a core circuit;
an embedded EPROM including a plurality of floating-gate cells, each floating gate cell having an output terminal that is selectively couplable to a corresponding portion of said core circuit;
a logic circuit having a plural of input terminals and a single output terminal;
means for applying predetermined voltages to a plurality of floating-gate cells of the embedded EPROM, whereby a floating gate of each of said plurality of floating-gate cells is subjected to a predetermined programming/unprogramming potential;
means for coupling a control gate of each of said floating-gate cells to a predetermined test bias voltage, and for coupling an output terminal of each of said floating-gate cells to an associated said input terminal of said logic circuit, whereby all of said of said floating-gate cells simultaneously transmit associated output signals to said logic circuit in response to said predetermined test bias voltage,
wherein the logic circuit includes means for generating on said single output terminal a single-bit cell test result signal having a first logic value when all of said plurality of floating-gate cells store a predetermined programmed/unprogrammed charge, and for generating said single-bit cell test result signal having a second logic value when one or more of said plurality of floating-gate cells fails to store said predetermined programmed/unprogrammed charge.
6. The integrated circuit according to claim 5 , further comprising means for transmitting said single-bit cell test result signal out of said integrated circuit to an external test system.
7. The integrated circuit according to claim 5 ,
wherein said means for applying said predetermined voltages comprises means for unprogramming said plurality of floating-gate cells, and
wherein said logic circuit comprises a wired NOR cell.
8. The integrated circuit according to claim 5 ,
wherein said means for applying said predetermined voltages comprises programming all of said plurality of floating-gate cells, and
wherein said logic circuit comprises a wired NAND cell.
9. The integrated circuit according to claim 5 , further comprising:
means for coupling a reference cell to a bias testing circuit and adjusting a system voltage of said integrated circuit such that a bias voltage generated by the reference cell is compared against a first predetermined reference voltage, wherein the bias testing circuit includes means for generating a single-bit bias test result signal having a first logic value when said bias voltage is greater than said first predetermined reference voltage, for generating said single-bit bias test result signal having a second logic value when said bias voltage is less than said first predetermined reference voltage, for generating said single-bit bias test result signal having the second logic value when said bias voltage is greater than said second predetermined reference voltage, and for generating said single-bit bias test result signal having the first logic value when said bias voltage is less than said second predetermined reference voltage.
10. The integrated circuit according to claim 5 , wherein the logic circuit comprises one of a DC-to-DC converter circuit and a low dropout regulator (LDO) circuit.