JPH0711920B2 - Programmable ROM - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a programmable ROM, and more particularly to a programmable ROM using a semiconductor element group having zener characteristics.

[Conventional technology]

When a programmable ROM is composed of semiconductor elements, a semiconductor element using a Zener diode has been proposed. This Zener diode is IEEJ Journal of Solid State Circuits, ESC October 1975, pp. 420-424 (IEEE JOURNAL OF SOLID-STATE CIRCUITS, Vol, SC-10
As described in DEC. (1975), different voltages are generated depending on the presence or absence of a short circuit in the junction. That is, the Zener diode generates a Zener voltage by the Zener effect before the short circuit of the junction by applying a reverse voltage. On the other hand, a Zener diode on the wafer is used for the Zener diode to selectively
When a voltage pulse is applied, the junction of the zener diode is destroyed, and the current is then short-circuited. When the junction is short-circuited, the Zener diode has a low resistance and generates a low voltage lower than the Zener voltage. Therefore, a high level voltage (zener voltage) or a low level voltage can be generated from the zener diode depending on whether or not the junction is short-circuited. Therefore, digital information can be stored in the Zener diode depending on whether or not the junction is short-circuited.

[Problems to be Solved by the Invention]

However, in the above-mentioned prior art, although the offset voltage of the operational amplifier can be adjusted to 0 by short-circuiting the junction of the zener diode, the value of the operating resistance when the junction of the zener diode is short-circuited depends on the element. When detecting whether or not the Zener diode is in the short-circuit state from the level of the output voltage of the Zener diode, there is a possibility that the short-circuit state of the Zener diode may not be accurately detected depending on the value of the operating resistance. As described in JP-A-57-191900, it is possible to detect the presence or absence of a short circuit in the semiconductor element by adopting a method of comparing the output voltage of the semiconductor element with a set voltage. . However, even if the set voltage is set higher than the average output voltage of the semiconductor element in which the junction is short-circuited, when the operating resistance value of the semiconductor element varies due to the junction short-circuit, the output voltage of the semiconductor element is It may be higher than the set voltage,
It becomes impossible to obtain an accurate binary signal conforming to the logic.

An object of the present invention is to output an accurate binary signal according to the presence / absence of a short circuit in the junction even if the junction of any semiconductor element in the semiconductor element group having the Zener characteristic is short-circuited according to the logic. Programmable ROM
To provide.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention provides a plurality of semiconductor elements that output different voltages depending on the presence or absence of a short circuit of a junction showing zener characteristics, a constant current source that supplies a constant current to each semiconductor element, and A short circuit for individually applying a signal for junction short circuit to the semiconductor element, a semiconductor element of the semiconductor element in which the junction is not short-circuited, and an output voltage of the semiconductor element in which the junction is short-circuited by the signal from the short circuit And a comparator that outputs each comparison result as a binary signal, the set voltage being lower than the minimum value of the Zener voltage of each semiconductor element, and the semiconductor element having a junction short-circuited. Is a programmable ROM that is set to a voltage higher than the maximum value of the output voltage of.

[Action]

According to the above-mentioned means, when the short-circuiting signal is applied to the junction of the semiconductor element designated according to the logic in the semiconductor element group through the short circuit, the junction of the designated semiconductor element is short-circuited. After this, when a constant current is supplied to each semiconductor element from the constant current source, the output voltage of the semiconductor element whose junction is not short-circuited is maintained at the Zener voltage, and the output voltage of the semiconductor element whose junction is short-circuited is more than the Zener voltage. Becomes a low voltage. Then, the output voltage of each semiconductor element is respectively compared with the set voltage by the comparator, and the comparison result according to the presence or absence of the short circuit of the junction is output as a binary signal.
In this case, the set voltage is set to a voltage lower than the minimum value of the Zener voltage of each semiconductor element and higher than the maximum value of the output voltage of the semiconductor element whose junction is short-circuited. Therefore, even if the zener voltage of the semiconductor element varies toward the lower side, the zener voltage does not become lower than the set voltage, and even if the operating resistance value of the semiconductor element due to the short circuit of the junction varies toward the higher side. The output voltage of the semiconductor element never becomes higher than the set voltage.
Therefore, even if the Zener voltage varies or the value of the operating resistance of the semiconductor element varies due to the short circuit of the junction, an accurate binary signal suitable for the logic can be output.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of a preferred embodiment for storing 3-bit information. In Fig. 1, Zener diodes ZD0, ZD1, and ZD2 are the bases of the transistors, respectively.
It uses an emitter junction diode, and the cathode (base) side is grounded via a resistor R10 and is connected to the trim pad COM. On the other hand, the anode (emitter) side is connected to the MOS transistors CC0, CC1 and CC2 via diodes D10, D11 and D12, respectively, and is also connected to the diodes D20 and D2 via resistors R20, R21 and R22, respectively.
1, D22 and inverters I0, I1, I2 are connected. Further, the anode sides of the Zener diodes ZD0, ZD1, ZD2 are connected to the trim pads PAD0, PAD1, PAD2, respectively. Diodes D10, D11, D12 are trim pad P
The MOS transistors CC0, CC1, CC2 are inserted between AD0, PAD1, PAD2 and the pad for trim COM to prevent breakdown of the MOS transistors CC0, CC1, CC2 when a current / voltage pulse is applied by probing. The resistor R10 is provided to limit the sneak current at this time. Also, resistors R20 and R2
1, R22 and diodes D20, D21, D22 are inverters I0, I1, I2
Has been inserted to protect the input side of.

MOS transistors CC0, CC1 and CC2 form a current mirror circuit with MOS transistor CM, and zener diodes ZD0 and ZD
It functions as a constant current source that supplies a constant current to 1 and ZD2. The MOS transistor CM is grounded via the diode DM and the resistor RM, and the current value of the constant current source is adjusted by the value of the resistor RM. The diode DM is
It is inserted to adjust the Early voltage of the MOS transistors CM, CC0, CC1, CC2.

The inverters I0, I1, I2 as comparators compare the output voltage of the Zener diodes ZD0, ZD1, ZD2 with the set voltage, and output each comparison result to the decoder 200 as a binary signal. The set voltage of each inverter I0, I1, I2 is set lower than the minimum value of Zener voltage of Zener diode ZD0, ZD1, ZD2 and higher than the maximum value of output voltage of Zener diode whose junction is short-circuited. There is. That is, as shown in FIG. 2, the set current supplied from the constant current source to each Zener diode is Ic to Ic.
variation in the range of c ', Zener voltage V _H is dynamic resistance ron several 10Ω~ number 10K of variation or, or Jiyankushiyon is shorted zener diode in the range of 4.2~V2.2V
It is set to 1V in consideration of the case where the output voltage V _L of the zener diode with the variation of Ω and the junction short-circuited varies from 0.2mV to 0.2V. That is, even if the Zener voltage varies to the lower side, the Zener voltage becomes lower than the set voltage, or the output voltage of the Zener diode becomes higher than the set voltage even if the operating resistance of the Zener diode with the short-circuited junction varies to the higher side. The set voltage is set to 1V so that it will not be damaged.

The decoder 200 is configured to close the contacts of the switches SW0 to SW7 according to the output levels of the inverters I0, I1, I2. For example, if the output level of the inverters I0, I1, I2 is "0",
When the output level is "0", "0", the switch SW0 contact is closed. When the output level is "0", "0", "1", the switch SW1 contact is closed, and the output level is "1", "1", " Switch SW for 1 "
Close the 7 contacts. As a result, 0, 1 from the output terminal Vout
/ 8V _{REF to} 7 / 8V _REF voltage is output.

In the above configuration, usually Zener diodes ZD0, ZD
Since constant current I _C is supplied to MOS transistors CC0, CC1 and CC2 to 1 and ZD2 respectively, zener diode ZD
A zener voltage V _H is generated from the outputs of 0, ZD1 and ZD2. Therefore, the output levels of the inverters I0, I1, I2 are all "0".

Here, the pads for trim PAD1 and COM
When a current / voltage pulse is applied between them, the Zener diode ZD1 breaks down and the Zener diode ZD1
The junction of D1 is short-circuited. As a result, the Zener diode ZD1 becomes an element equivalent to a low resistance resistance element, and the output voltage of the Zener diode ZD1 becomes the low voltage V _L. This voltage V _L is 0 when the current I _C is set to 10 μA.
Since it is within the range of 2mV to 0.2V, the output level of the inverter I1 is inverted from "0" to "1". For this reason the decoder 200
In response to a command from the switch SW2, the contact of the switch SW2 is closed, and a voltage of 2/8 _REF is output from the output terminal Vout.

Thus, in this embodiment, the Zener diode ZD
Since a constant current is supplied to each of 0, ZD1, and ZD2 to detect the output voltage of each Zener diode, even if the Zener voltage varies or the operating resistance of the Zener diode varies, the presence or absence of a short circuit in the junction Accordingly, the output voltage of the Zener diode can be accurately detected.

In addition, when performing the zapping process to short the junction of the zener diode, zener diodes ZD0 to ZD2
Since the cathode side of each is connected to the trim pad COM, multiple zener diodes can be collectively zapped, which can speed up the zapping process and simplify the power supply equipment for the zapping. You can

Also, as shown in FIG. 3, MOS transistors CC0, CC
Even if the constant current circuit is configured by reversing the positions of 1, CC2, CM and the Zener diodes ZD0, ZD1, ZD2, the same effect as in the above embodiment can be obtained.

Further, as shown in FIG. 4, comparators CMP0, CMP1, CMP2 are used instead of the inverters I0, I1, I2, and resistors R100, R101, R1 are used instead of the MOS transistors CC0, CC1, CC2, CM.
Even if 02 and RN are used, it is possible to obtain the same effect as that of the above-mentioned embodiment. The resistors R100, R101, R102 are of high resistance so as to form a constant current source. That is, the resistance of the Zener diodes ZD0, ZD1, and ZD2 in the open state is roff, the resistance in the short-circuited state is ron, and the resistors R100, R101, R
If the resistance R _{L of} 102 is satisfied, and if this satisfies the relationship of roff <R _L <ron, the resistance R _L can be set to a large value.
Can be regarded as a constant current source.

Further, the set currents of the comparators CMP0 to CMP2 can be arbitrarily set by the ratio of the resistors RN and RM. Therefore, comparator CMP0 ~
If the set voltage of CMP2 is set to 1V, the same effect as that of the above embodiment can be obtained.

In each of the above embodiments, the Zener diode ZD0
Although ~ ZD2 described above uses the transistor base-emitter junction diode, the same effect can be obtained by connecting the transistor collector to the base. Even if it is not an NPN type transistor,
Type transistors can also be used. Furthermore, I0
For ~ I2, a single channel MOS transistor or a MOS transistor can be used.

Further, as the diodes DM, D10 to D12, D20 to D22, it is desirable to use a base-collector junction diode having a high breakdown voltage. In this case, the same effect can be obtained even if the emitter is joined to the base.

Furthermore, the present embodiment can be applied to an m: n matrix structure.

〔The invention's effect〕

As described above, according to the present invention, a constant current is supplied to each semiconductor element, the output voltage of each semiconductor element is compared with the set voltage, and the comparison result according to the presence or absence of a junction short-circuit is calculated. It is detected by the value signal and the set voltage is set to a voltage lower than the minimum value of the Zener voltage of each semiconductor element and higher than the maximum value of the output voltage of the semiconductor element whose junction is short-circuited. Even if the Zener voltage varies or the value of the operating resistance of the semiconductor element varies due to the short circuit of the junction, an accurate binary signal conforming to the logic can be output as digital information.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram of a Zener diode showing a relationship between voltage and current, and FIG. 3 is a configuration diagram showing an embodiment of the present invention, FIG. FIG. 6 is a configuration diagram showing still another embodiment of the present invention. ZD0, ZD1, ZD2 …… Zener diode, I0, I1, I2 …… Inverter, CC0, CC1, CC2, CM …… MOS transistor, COM, P
AD0, PAD1, PAD2 …… Pad for trim, CMP0, CMP1, CMP2…
… Comparator, 200… Decoder.

Claims (1)

[Claims] 1. A plurality of semiconductor elements that output different voltages depending on the presence or absence of a short circuit of a junction showing zener characteristics, a constant current source that supplies a constant current to each semiconductor element, and a junction short circuit for each semiconductor element. Short circuit for applying signals individually, output voltage of the semiconductor element of which the junction is not short-circuited among the semiconductor elements and the semiconductor element of which the junction is short-circuited by the signal from the short circuit are respectively compared with the set voltage. A comparator for outputting each comparison result as a binary signal, wherein the set voltage is lower than the minimum value of the Zener voltage of each of the semiconductor elements and is higher than the maximum value of the output voltage of the semiconductor element whose junction is short-circuited. Programmable RO that is also set to a high voltage
M.