JPH0394516A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To extract an output signal without giving mutual effect onto an internal function block by installing two transistors(TRs) in series between the internal function block and an output terminal, and installing one TR between nodes of the TRs and ground. CONSTITUTION:An output circuit 22 has two output signal selection TRs and a TR fixing a node between th two TRs in an output node from each internal function block. When an output signal of an internal function block 11 is led to an output terminal 22, TRs 13, 14, 21 are turned on and Trs 16, 18, 19 are turned off. Since an output signal from the internal function block 11 is leaked through a drain-source capacitance of the Tr 19, since it flows to ground, the effect of the internal function 11 onto the internal function block 17 is interrupted. Moreover, when the output signal of the internal function block 17 is led to the output terminal 12, the TR 16 is similarly turned on and the effect of the internal function block 17 onto the internal function block 11 is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to semiconductor integrated circuits such as microcomputers integrated on one chip, and particularly to an output circuit that outputs output signals from internal functional blocks. It is.

Conventional technology Conventionally, when selecting from among the output signals of two or more internal functional blocks such as an AD converter built into a microcomputer integrated on one chip and outputting it to the outside, an output configured with a transistor is used. The output signal is switched using a signal selection circuit.

FIG. 2 shows an example of a conventional output circuit. In FIG. 2, transistors 4 and 5 are connected between the internal EIA block 1.2 and the output terminal 3, respectively, in order to select the output signal from the internal function block 1.2 as required and lead it to the output terminal 3. has been established.

Here, when the output signal of the internal function block 1 is to be led to the output terminal 3, the transistor 4 is turned on and the transistor 5 is turned off, and when the output signal of the internal function block 2 is to be led to the output terminal 3, the transistor 4 is turned on and the transistor 5 is turned off. Turn off transistor 4,
Transistor 5 was turned on.

Problem to be Solved by the Invention However, in the conventional structure described above, if a capacitance exists between the drain and source of the MOS transistor and the output signal of the internal functional block 1 is led to the output terminal 3, the transistor 5 is off, the output signal of internal function block 1 may be coupled to the output signal of internal #Ja block 2 due to the drain-source capacitance, which may cause malfunction of internal function block 2. The problem was that the

The present invention solves the above-mentioned conventional problems, and aims to provide a semiconductor integrated circuit having an output circuit that can take out output signals without mutually influencing internal functional blocks.

Means for Solving the Problems In order to solve the above problems, the semiconductor integrated circuit of the present invention includes:
It has an output circuit in which two transistors are each installed in series between at least two internal functional blocks and an output terminal, and one transistor is installed between a node between the two transistors and ground. .

Effect When selecting the output signal of each internal functional block and deriving it to the output terminal with the above structure, two The transistor is turned on so that the output is output to the output terminal, and a fixed node is connected between the node between the two transistors connected in series between the internal functional block other than the output terminal and the output terminal, and the ground. Even if the transistor is turned on and the output signal leaks through the drain-source capacitance of the transistor connected from the output terminal to an internal functional block other than the output side, the output signal is connected to the output side by grounding through the transistor for fixing the node. Prevents transmission to other internal functional blocks. Therefore, the influence of each internal functional block on each other is cut off, and each internal functional block operates normally.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is an output circuit diagram in a semiconductor integrated circuit showing one embodiment of the present invention. In FIG. 1, two transistors are connected in series between the internal function block 11 and the output terminal 12.13. 14, and these two transistors 13. A transistor 16 is installed between the signal transmission node 15 between the nodes 14 and the ground. Furthermore, two transistors 18.19 are installed in series between the internal function block 17 and the output terminal 12, and these two transistors 18. A transistor 21 is installed between a signal transmission node 20 between the transistors 19 and the ground.

In this way, the output circuit 22 has two transistors for output signal selection and one transistor for fixing the node between these two transistors at the output node from each internal functional block.

The operation of the above structure will be explained below.

When outputting the output signal of the internal function block 11 to the output terminal 12, the transistors 13, 14, and 21 are turned on.
Transistors 16, 18. 19 is turned off. In other words, when the transistor 21 is on, the signal transmission node 20 is grounded, and even if the output signal from the internal functional block 11 leaks through the drain-source capacitance of the transistor 19, it is grounded. The influence of the internal function 11 on the function block 17 is blocked.

In addition, the output signal of the internal function block 17 is sent to the output terminal 12.
Similarly, when deriving internal function block 1 to internal function block 11, transistor 16 is turned on.
The influence of 7 will be blocked.

Effects of the Invention As described above, according to the present invention, output signals can be extracted without mutually influencing each internal functional block.

[Brief explanation of drawings]

FIG. 1 is an output circuit diagram of a semiconductor integrated circuit showing an embodiment of the present invention, and FIG. 2 is an output circuit diagram of a conventional semiconductor integrated circuit. 11.17... Internal function block, 12... Output terminal, 13, 14, 16, 18, 19.21...
・Transistor, 15.20...Signal transmission node, 2
2...Output circuit.

Claims (1)

[Claims] 1. A semiconductor having an output circuit in which two transistors are each installed in series between at least two internal functional blocks and an output terminal, and one transistor is installed between the node between the two transistors and ground. integrated circuit.