Semiconductor device and error correction method
A device is provided with: memory cell array including plurality of first and second memory cells and one or more third memory cells; judging circuit that judges plurality of data values held by selected first and second memory cells of the first and second memory cells, by referring to reference potential corresponding to reference data held by a selected third memory cell; and error detection and correction circuit that detects whether or not there is error in the judged data values of the first and/or second memory cells, with judged data value of the first and second memory cells as error correcting code. When the error detection and correction circuit detects that there is error exceeding error correction capability in the judged data values, control is performed to write reference data to the selected third memory cell.
1. A semiconductor device, comprising:
a memory cell array including a plurality of first memory cells, a plurality of second memory cells, and one or more third memory cells;
a judging circuit that judges a plurality of data values held by selected first memory cells of the plurality of first memory cells and selected second memory cells of the plurality of second memory cells, by referring to a reference signal corresponding to reference data held by at least one selected third memory cell of the one or more third memory cells; and
an error detection and correction circuit that detects whether or not there is an error in the judged data values of the plurality of first and/or second memory cells, with the judged data value of the plurality of first and second memory cells as an error correcting code; wherein,
the error detection and correction circuit, on detecting that there is an error exceeding error correction capability in the judged data values of the plurality of first and/or second memory cells, performs control to rewrite the reference data to the at least one selected third memory cell of one or more third memory cells.
2. The semiconductor device according to claim 1 , wherein the error detection and correction circuit comprises:
a syndrome generation unit that generates a syndrome from the judged data values of the plurality of first and second memory cells;
a syndrome decoder that identifies a location of data where an error has occurred among the judged data values of the plurality of first and second memory cells from the generated syndrome; and
an error correction unit that outputs an inverted control signal to invert, with regard to the data at the location identified by the syndrome decoder, the data value; wherein
the error detection and correction circuit, after performing error correction based on the inverted control signal outputted by the error correction unit, in a case where the syndrome generated by the syndrome generation unit indicates that an error is present; detects that there is an error exceeding error correction capability.
3. The semiconductor device according to claim 1 , further comprising a reference read write unit that comprises:
a reference read circuit that reads the reference data held in the selected at least one of third memory cells, and outputs a reference signal corresponding to the reference data; and
a reference write circuit that writes the reference data to the selected at least one of third memory cells.
4. The semiconductor device according to claim 3 , wherein
the third memory cell comprises a memory cell that holds data of a first logic value, and a memory cell that holds data of a second logic value;
the reference read circuit outputs a signal at an intermediate level between two signals respectively read from memory cells holding data of the first and second logic values corresponding to the selected at least one of third memory cells, as a reference signal corresponding to the reference data; and
the reference write circuit writes data of each of the first and second logic values to memory cells holding data of the first and second logic values corresponding to the selected at least one of third memory cells.
5. The semiconductor device according to claim 4 , wherein the reference read write unit comprises:
a first reference bit line connected to a memory cell that holds data of the first logic value among the third memory cells;
a second reference bit line connected to a memory cell that holds data of the second logic value among the third memory cells; and
first and second transistors connected in series between the first reference bit line and the second reference bit line; wherein
the reference signal is outputted from a connection node of the first transistor and the second transistor.
6. The semiconductor device according to claim comprising:
a word line connected between a control electrode of the plurality of first and second memory cells, and a control electrode of the third memory cell; wherein
the semiconductor device is configured such that the third memory cell that outputs the reference signal is selected by the word line.
7. The semiconductor device according to claim 1 , wherein
data held by the plurality of first memory cells is a data bit for external input/output, and
data held by the plurality of second memory cells is a check hit attached for error correction of the data bit.
8. The semiconductor device according to claim 7 , further comprising an output buffer that outputs the data bit to the outside, wherein
the error detection and correction circuit outputs an error signal in a case of detecting an error exceeding error correction capability, and
the output buffer receives the error signal and performs control so that a data bit held by the plurality of first memory cells is not outputted to the outside.
9. The semiconductor device according to claim 3 , further comprising:
a write control circuit that performs write control with regard to the plurality of first and second memory cells; wherein
the write control circuit performs control to write an error-corrected data value to a memory cell corresponding to the data on which error correction has been performed based on the inverted control signal, among the selected plurality of first memory cells, in a prescribed write period, and
performs control to write a data value of the selected plurality of second memory cells in the prescribed write period.
10. The semiconductor device according to claim 3 , further comprising:
a write control circuit that performs write control with regard to the plurality of first and second memory cells; wherein
the write control circuit performs control to write the error-corrected data value to a memory cell corresponding to data on which error correction has been performed based on the inverted control signal, among the selected plurality of first and second memory cells, in a prescribed write period.
11. The semiconductor device according to claim 9 , wherein the write control circuit comprises:
a rewrite node;
a precharge circuit that precharges the rewrite node to a prescribed potential; and
a third transistor having a gate that receives the inverted control signal, and in which one of a source and drain is connected to the rewrite node; and another of the source and drain is connected to a first power supply; wherein
the write control circuit performs control to write the error-corrected data value, based on the potential of the rewrite node, in a prescribed write period.
12. The semiconductor device according to claim 1 , wherein the first memory cells, the second memory cells and the third memory cells are memory cells comprising a resistance variable memory element that stores information according to resistance state.