JPS58186838A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To set the threshold voltage of an input circuit to a desired value easily, by setting the output of a D/A comparator circuit by a program, and regarding its output value as a reference voltage value for the operation of a comparator. CONSTITUTION:A comparison input voltage is led from an input terminal 10 to the comparator circuit 11. The output voltage of the D/A converter circuit 12 is led as the reference input. This output voltage is given through a data table 13 by a digital input set by a user's in-use program when an integrated circuit is used. When the input voltage is lower than the output voltage, the comparison output of the comparator 11 is at a power supply potential VDD. When the input voltage exceeds the output voltage, on the other hand, the comparison output is at the earth potential. This operation means that the threshold voltage of the input circuit is set to the desired value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor integrated circuit for, for example, a microcomputer, and particularly to an input circuit thereof.

[Technical background of the invention and its problems]

Conventionally, the threshold voltage of an input circuit of a semiconductor integrated circuit has a unique value for each integrated circuit. For this reason, input specifications determined by the type of external input device such as an integrated circuit for a microcomputer (for example, input low level voltage ■L is TT
If it is necessary to change the threshold value of the input circuit of an integrated circuit according to the L specification (0.8■ for the key manual specification and 1.3■ for the key manual specification), conventionally the mask pattern design has not been changed for each integrated circuit. However, production efficiency was poor and product costs tended to be high.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a semiconductor integrated circuit in which the dark voltage of the input circuit can be easily set to a desired value during use, and the input circuit has great versatility.

[Summary of the invention]

That is, in the semiconductor integrated circuit of the present invention, the output of a converter circuit whose digital input is set by a program is used as a reference voltage, and a comparator circuit compares and determines this reference voltage with an input voltage from an input terminal. The output is used as an input signal for the subsequent circuit. Therefore, the threshold voltage of the input circuit can be easily set to a desired value by a program, and the versatility of the input circuit is increased.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an input circuit portion of a semiconductor integrated circuit for a microcomputer, for example, and 10 is an input terminal, which is connected to an external input pin (not shown). No. 1 is a comparator circuit, to which the input voltage Vin from the input terminal 10 is led as a comparison input, and the output voltage from the A (digital/analog) converter circuit 12 is led as a reference input. The comparison output is given to the next stage circuit (not shown) as an input signal. the above"/
The A converter circuit 12 is provided with a digital input set by the user's program when using the integrated circuit. For example, data from a ROM (read only memory) containing the user's program is input through the data table 13. do.

Note that the comparator circuit 11 is connected to N
It consists of a differential amplification circuit using a channel E/D circuit, and has an enhancement (square MO8) transistor T.
8. The drain of 'r2 is connected to the VDD power supply via depletion 0 type MO8) transistors T8+T4 for load resistance, and the drain of the transistors Tl+'l2
The sources of M are connected in common and constant current source type M
O8 transistor T. is grounded through common.

The D//A converter circuit 12 uses, for example, a ladder-type resistor circuit as shown in the figure, and symbol (2) is an inverter.

In the above configuration, when the output voltage of the converter circuit 12 is set to ■1 by the program input, the input terminal Vin of the input terminal 1θ is set to ■, and below, in the comparator circuit 11, the reference voltage input side transistor T.

is turned on, so the transistor T2 on the comparison voltage input side, whose source end is common to that of this transistor T2,
is off, and approximately the VDD potential appears as a comparative output via the transistor T. On the other hand, when the input voltage Vin exceeds V, the transistor on the comparison input side]
Since "1" is turned on, the comparison outputs are transistors T and T. Approximately ground potential appears through. At this time, the transistor T2 on the reference input side is turned off. That is, the above operation means that the threshold voltage of the input circuit of the integrated circuit is set to 1. Similarly, the output voltage of the D/A converter circuit 12 is
+..., the threshold voltage of the -F input circuit is set to ■tz..., and this situation is shown in FIG.

That is, according to the above-described integrated circuit, the user can set the output value of the /A converter circuit 12 by a program according to the required input specifications, and operate the comparator circuit 11 using the output value as a reference voltage. According to
The input circuit threshold voltage can be easily set to a desired value.

It should be noted that the configurations of the comparator circuit 11 and the DA converter circuit 12 are not limited to the above example, and may be configured using, for example, a CM 08 circuit. Alternatively, the comparison output of the comparator circuit 11 may be extracted from the drain of the reference input terminal transistor T2 to obtain an in-phase component with the input voltage.

〔Effect of the invention〕

As described above, according to the semiconductor integrated circuit of the present invention, since the input circuit threshold voltage can be easily set to a desired value by a program during use, a margin can be provided in design and manufacturing. In addition, when applied to microcomputers, for example, it can be used by a wide range of users, and the specifications of the input circuit can be satisfied just by designing one microcomputer, so different microcomputers with different threshold voltages can be used. Compared to manufacturing, production efficiency is better and product costs are lower.

[Brief explanation of drawings]

FIG. 11 is a circuit diagram showing an embodiment of the semiconductor integrated circuit according to the present invention, and FIG. 2 is a characteristic diagram shown for explaining the operation of FIG. 1. 10... Input terminal 11... Comparator circuit 12... Converter circuit, patent attorney Patent attorney Suzue Takehiko

Claims (2)

[Claims] (1) A semiconductor integrated circuit comprising an input circuit whose voltage is determined by a reference voltage set by a program. (2) The input circuit is a comparator circuit that compares and determines the input voltage from the input terminal and the reference voltage, and the reference voltage is a D/A converter circuit that D/A converts digital input set by a program. 2. The semiconductor integrated circuit according to claim 1, wherein the output voltage is .