Semiconductor memory circuit

• US 5,339,271 A
• Filed: 03/04/1992
• Issued: 08/16/1994
• Est. Priority Date: 03/05/1991
• Status: Expired due to Term

• Current Assignee: Oki Semiconductor Company Limited (ROHM Co., Ltd.)
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Tanagawa, Kouji
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): ZARABIAN, AMIR
• Application Number:
  US07/846,205
• Time in Patent Office: 895 Days
• Field of Search: 371/21.4, 365/189.04, 365/218, 365/185, 365/190, 365/189.07
• US Class Current: 365/185.24
• CPC Class Codes: G06F 2201/81 Threshold
• CPC Class Codes: G11C 16/04 using variable threshold transistors, e.g. FAMOS
• CPC Class Codes: G11C 16/0441 comprising cells containing multiple floating gate devices, e.g. separate read-and-write FAMOS transistors with connected floating gates
• CPC Class Codes: G11C 16/10 Programming or data input circuits
• CPC Class Codes: G11C 16/34 Determination of programming status, e.g. threshold voltage, overprogramming or underprogramming, retention
• CPC Class Codes: G11C 29/50 Marginal testing, e.g. race, voltage or current testing
• CPC Class Codes: G11C 29/50004 of threshold voltage
• CPC Class Codes: G11C 8/08 Word line control circuits, e.g. drivers, boosters, pull-up circuits, pull-down circuits, precharging circuits, for word lines

Abstract

A semiconductor memory circuit includes memory cells each having two storage semiconductor elements. One of these semiconductor elements is made inoperative in response to a first or a second operation control signal. This makes it possible to check the margin of a threshold voltage of the other storage semiconductor element at the time when writing, erasing and reading operations with respect thereto are being performed.

Claims

1. A semiconductor memory circuit having memory cells for storing data therein, comprising:

the memory cells for storing data, each memory cell including two storage semiconductor elements, the storage semiconductor elements being permitted to have their operations stopped, respectively, in response to a first operation control signal and a second operation control signal;

a data control circuit for performing reading, writing and erasing of data with respect to the two storage semiconductor elements of the memory cell, the data control circuit being adapted to supply a first level of voltage to each of the storage semiconductor elements so as to write data into a first one of the storage semiconductor elements and at the same time to erase data written in a second one of said storage semiconductor elements, the data control circuit being additionally adapted to amplify the data read out from the storage semiconductor element to generate an output data signal; and

a data selector circuit for selecting the memory cell, with respect to which reading-out, writing-in and erasing of data are performed, in response to address data, the data selector circuit being adapted to supply said first level of voltage to a word line of the selected memory cell.

2. A semiconductor memory circuit as set forth in claim 1, wherein the two storage semiconductor elements of the memory cell each is constituted by a floating-gate type transistor permitting electrical writing, reading-out, and erasing of data to be performed with respect thereto, the first storage semiconductor element having a gate connected to a drain of the second storage semiconductor element, the second storage semiconductor element having a gate connected to a drain of the first storage semiconductor element, the first and second storage semiconductor elements having their sources grounded via a first and a second switch circuit, respectively.

3. A semiconductor memory circuit as set forth in claim 2, wherein the first and the second switch circuits respectively operate in response to the first and said second operation control signals.

4. A semiconductor memory circuit as set forth in claim 2, wherein the first and the second switch circuits are constituted by transistors, respectively.

5. A semiconductor memory circuit as set forth in claim 1, wherein the data control circuit is composed of a write-in circuit for writing data into the memory cell and a data input/output circuit for inputting and outputting data.

6. A semiconductor memory circuit as set forth in claim 5, wherein the write-in circuit includes two voltage boosting circuits for supplying to the two storage semiconductor elements of the memory cell said first level of voltage for activation thereof.

7. A semiconductor memory circuit as set forth in claim 6, wherein the two voltage boosting circuit activate only one of the two storage semiconductor elements in response to data inputted into the semiconductor memory circuit.

8. A semiconductor memory circuit as set forth in claim 6, wherein a first one of the two voltage boosting circuit supplies said first level of voltage to a drain of the first storage semiconductor element in the memory cell and to a gate of the second storage semiconductor element in the memory cell.

9. A semiconductor memory circuit as set forth in claim 6, wherein a second one of the two voltage boosting circuits supplies said first level of voltage to a drain of the second storage semiconductor element in the memory cell and a gate of the first storage semiconductor element in the memory cell.

10. A semiconductor memory circuit as set forth in claim 8, wherein the first level of voltage supplied by the first voltage boosting circuit is supplied via a third switch circuit as well as via a first one of complementary first and second bit lines.

11. A semiconductor memory circuit as set forth in claim 10, wherein the third switch circuit is constituted by a transistor and is operative in corresponding relation to a condition of the word line.

12. A semiconductor memory circuit as set forth in claim 10, wherein the first level of voltage supplied by the first voltage boosting circuit is supplied via a fourth switch circuit as well as via a second one of said complementary first and second bit lines.

13. A semiconductor memory circuit as set forth in claim 12, wherein the fourth switch circuit is constituted by a transistor and is operative in corresponding relation to a condition of the word line.

14. A semiconductor memory circuit as set forth in claim 5, wherein the data input/output circuit includes a differential amplifier circuit for effecting differential amplification of data read out from the two storage semiconductor elements in the memory cell.

15. A semiconductor memory circuit as set forth in claim 14, wherein the differential amplifier circuit includes fifth and sixth switch circuits each being constituted by a respective transistor, the fifth switch circuit being disposed between a first bit line and a line for supplying a second voltage level and having a gate connected to a second bit line, the sixth switch circuit being interposed between the second bit line and the line for supplying the second voltage level and having a gate connected to the first bit line.

16. A semiconductor memory circuit as set forth in claim 15, wherein the differential amplifier circuit includes seventh and eighth switch circuits, the seventh switch circuit being interposed between a gate of the fifth switch circuit and the second bit line, the eighth switch circuit being disposed between a gate of the sixth switch circuit and the first bit line, the seventh and eighth switch circuits being operative in response to a third operation control signal.

17. A semiconductor memory circuit as set forth in claim 16, wherein the differential amplifier circuit includes ninth and tenth switch circuits, the ninth and tenth switch circuits being operative in response to a third operation control signal to supply a third voltage level to gates of the fifth and sixth switch circuits, respectively.

18. A semiconductor memory circuit as set forth in claim 16, wherein the seventh and eighth switch circuits perform their operations which are counter to those of the ninth and tenth switch circuits.

19. A semiconductor memory circuit as set forth in claim 5, wherein the data input/output circuit includes a read-out circuit for comparing to each other two data read out from the two storage semiconductor elements in the memory cell to generate an output binary signal.

20. A semiconductor memory circuit as set forth in claim 19, wherein the two data read out from the two storage semiconductor elements are inputted into two AND circuits included in the read-out circuit, output signals from the two AND circuits are sent to set and reset terminals of a flip-flop circuit, respectively, and an output signal from the flip-flop circuit provides said output binary signal.

21. A semiconductor memory circuit as set forth in claim 19, wherein the read-out circuit includes an abnormality sensing circuit which, at the time when the two data read out from the two storage semiconductor elements are abnormal, provides information on this abnormality.

22. A semiconductor memory circuit as set forth in claim 21, wherein the abnormality sensing circuit is constituted by a NOR circuit.

23. A semiconductor memory circuit as set forth in claim 19, wherein the read-out circuit is a sense amplifier.

24. A semiconductor memory circuit as set forth in claim 1, wherein the first voltage level is a high level of voltage.

25. A semiconductor memory circuit as set forth in claim 15, wherein the second voltage level is a power source voltage.

26. A semiconductor memory circuit as set forth in claim 17, wherein the third voltage level is a ground voltage.