JPH01284782A - Rom code number readout circuit - Google Patents

Abstract

PURPOSE:To easily read out a ROM code number by switching output signals from plural transistor pairs where the ROM code number is written and a ROM with a test signal and exclusively outputting them to ROM output terminals. CONSTITUTION:At the time of reading out the ROM code number, the test signal TEST is set in '1' and the connection points of two N channel transistors which are connected in series are connected to invertors 109-112 to output the signals to the output terminals PAD1-PAD12. At the time of outputting '0' by setting the output signals OUT 1 and 2 of the ROMs 113 and 114, ions are poured in order to synchronize with the N channel transistors 101 and 103. At the time of outputting '1' by setting the output signals OUT 1 and 2 of the ROMs 113 and 114, ions are poured in order to synchronize with the N channel transistors 100 and 102.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a ROM code number reading circuit, particularly a ROM code assigned to identify the contents of a ROM in an integrated circuit including an ion implantation switching type ROM. It relates to a circuit that reads out numbers.

[Conventional technology]

Generally, when manufacturing integrated circuits that include ion implantation switching type ROMs, lots with different ROM contents are run through the production line at the same time, and in such cases, the ROM
There is a possibility that contamination with different lots with different contents may occur in products assembled using wafers or resin sealing, and it becomes necessary to read and confirm the contents of the ROM of wafers or resin-sealed products.

In integrated circuits containing ion implantation switching type ROMs, no trace of ion implantation is left on the wafer, so even if a code number that identifies the contents of the ROM is implanted on the ion implantation mask, the wafer remains unchanged. It is not possible to know the identification code number just by looking at the exterior with a microscope.

Conventionally, in order to know the code number for identifying the contents of a ROM from a wafer, as shown in FIG. The number of N-channel transistors 301 to 312 connected to PAD 12' is arranged in the number necessary to represent the ROM code number, and this is read out.

In this case, the 1's digit and the 10's digit of the 3 decimal digits.

Each 100 digit is represented by 4 bits, 000 to 99
A code number for identifying the contents of ROM 9 can be displayed. The 1s digit is an N-channel transistor 301
．． The tens place is an N-channel transistor 305.100
It is assumed that the N-channel transistor 309 represents the LSB.

If the ROM code number is "024", N-channel transistors 303 and 3 in FIG.
The ions are implanted at 06. In an ion-implanted N-channel transistor, even if the gate is connected to GND, a train current flows when a voltage is applied to the drain, so the test pad PAD 1' in Figure 3
~When a probe is connected to PAD 12' and current flows, °°1
If no current flows, it is determined to be 0°.

Since ions are not implanted in the 100's digit, no current flows through the N-channel transistors 309 to 312, and the result is ``o o o o'' in binary notation, which reads ``0'' in the lO base, and the 10's digit is the N-channel transistor 306. Since ions are implanted into the
Therefore, the decimal number "2" can be read, and the 1's digit is ion-implanted into the N-channel transistor 303, so it is 2.
Since the decimal number is "0010°" and the decimal number "4" can be read, the 3-digit decimal ROM code number "024" can be read.

[Problem to be solved by the invention]

The conventional ROM code number successive circuit described above has a test pad on the wafer that reads out the code number that identifies the contents of the ROM, in addition to the normal bonding pad of the semiconductor integrated circuit. When reading out the identifying code number, the test probe must be placed on the test pad, but this is not easy because the probe must be operated manually using a probe connection device.

Furthermore, since the code number can only be read in the wafer state, there is a fatal drawback in that the code number cannot be read in products that are assembled with resin sealing.

In contrast to the conventional ROM code number reading circuit described above, the present invention connects the sources of two N-channel transistors to the power supply and GND, the gates to GND, and the drains of each transistor, and connects the signal at the connection point to the internal The test signal is used to switch the ROM of the test signal and output it to the output terminal of the ROM. One of the two transistors has a ROM
By implanting ions to output "1'" corresponding to the bit contents that make up the code number, and switching and outputting these binary information to the output terminal of the ROM, the RO
It has an original content that allows you to know the M code number.

[Means to solve the problem]

The ROM code number serialization circuit of the present invention is a circuit for reading out a ROM code number in an integrated circuit including an ion implantation switching type ROM. a transfer gate that switches the common output of each transistor pair and the bit output of the ROM in response to a test signal and outputs it exclusively to the output terminal of the ROM; It is characterized by having the following.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention, which corresponds to a 12-bit output ROM.

Each pair, 100 and 101, 102 and 103, etc., has two N-channels connected to the source, power supply, and GND, each gate to GND, and one train to the drain of the other for ion implantation. Transistor, 10
5 and 1O11 are N-channel transistors 100 and 1
107 and 106 are the connection point between N-channel transistors 102 and 103, and the transfer gate that switches the output signal 0UTI of the ROM 113.
114 is a transfer gate for switching the output signal OU "f'2; 108 is an inverter for inverting the test signal;
109 to 112 are inverters and PADs for output buffers
1 to PAD 12 are output terminals of the ROM.

When the test signal TEST is set to 0 during normal operation, the output signals 0UTI and 0 from ROM113 and 114 are
UT2 is output to output terminals PAD1-I) AD12.

When reading the ROM code number, use the test signal TEST
is set to 1'°, and the connection points of two N-channel transistors connected in series are output to output terminals PAD 1 to PAD 12 through inverters 109 to 112.

Output signals of ROM113, 114 0UTI, OU'r
2, if it does not reach 0°, ion implantation is performed to synchronize the N-channel transistors 101 and 103, and the output signal 0U of the ROM 113 and 1111 is
When outputting °゛1'' as TI, 0UT2, perform ion implantation to synchronize with N channel transistors 100 and 102. ROM code number 0 in 3 decimal digits.
When representing 00 to 999, 12 output terminals may be used since the binary number represents a decimal number of 4 bits and 1 digit.

In this way, if ions are implanted into either the power supply side or GND side transistor according to the number that identifies the contents of the ROM, by setting the test signal TEST to °°1'°, , output terminals PAD1 to PA
A code number for identifying the ROM contents can be output to D12.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.
This corresponds to a bit output ROM.

200 to 211 are N-channel transistors whose gates are connected to GND and whose drains are connected to each other in order to perform synchronized ion implantation;
2 and 203, 204 and 205 are 1's digit, 10's digit, 10
LSB of 0 digit, 206 and 207, 208 and 209, 2
10 and 211 are the MSB of 1's digit, 10's digit, and 100's digit
used to represent each. 212-219 are 2
The signal at the connection point of N-channel transistors connected in series and the output signal ou'r from the ROM (not shown)
Transfer gate that switches i~0UT4, 224~
229 is four 7A gates and two inverters that constitute a decoder for the test signals TESTI and TEST2, 230 to 223 are inverters for output buffers, and PA
D1 to PAD4 are output terminals of the ROM.

During normal operation, if both test signals TESTl and TEST2 are set to "o", the output signals 0UTI to 0U
The signal of T4 is output to output terminals PAD1 to PAD4.

When reading the ROM code number, read the 4-bit binary number as 1.
The 1's digit, the 10's digit, and the 100's digit expressed in decimal numbers are each transmitted as a test signal TESTI.

Corresponding to the states of TEFT2"01", "10°°, °"11"', RO is applied to the output terminals PAD1 to PAD4.
Output M code number.

In this embodiment, by using two test signals, R
The number of ROM output signals from which OM code numbers are read out at one time can be significantly reduced from 12 in the first embodiment to 4, which has the advantage of being applicable to ROMs with a small number of output bits.

In the above embodiment, the ROM code number is 1.
Although we will explain the case of a 3-digit decimal number, it is clear that an appropriate number of bits may be selected depending on the number of digits of the number identifying the contents of the ROM.

[Effects of the Invention] As explained above, the present invention has a configuration in which a plurality of transistor pairs in which ROM code numbers are written and a ROM output signal are switched by a test signal and output exclusively to the ROM output terminal. , a number that easily identifies the contents of the ROM by simply connecting the probe card needle to the output of a normal ROM in the wafer state, without the complicated operation of connecting the probe to the test pad as in the past. can be read. In addition, even in products sealed and assembled with resin, I
This has an unprecedented effect in that the identification number of the ROM can be read directly from the C bin.

In particular, when checking the number that identifies the contents of the ROM due to mixing with another lot with different ROM contents, it is easy to
Since the number identifying the contents of the ROM can be read, it is very effective in checking the readout of the contents of the ROM.

In addition, during wafer P/W testing, the tester automatically reads the wafer's ROM number, selects a test pattern that corresponds to the ROM contents, and performs a test T-L to test lots with different ROM contents in small quantities and in a wide variety of products. It is also possible to perform P/W tests continuously.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the invention, FIG. 2 is a circuit diagram showing a second embodiment of the invention, and FIG. 3 is a conventional circuit diagram. 100~103, 200~211, 301~312...
・N-channel transistor, 104-107.212
~219...Transfer Gate, 108.109~
112,230-233,228°229...Inverter for inverting transfer gate switching signal, 113・R
OM, 224-227...Noah Gate, PAD 1
~PAD12...Output terminal, PAD'~PAD12
'...Test pad.

Claims (1)

[Claims] R in an integrated circuit including an ion implantation switching type ROM
A circuit for reading out an OM code number, consisting of two transistor pairs each having ions implanted into one side so as to represent the contents of the bits constituting the code number, the number of which is the same as the number of bits, and a common output of each transistor pair. and a transfer gate that switches the bit output of the ROM in response to a test signal and outputs it exclusively to the output terminal of the ROM.