JPH05315933A - Output circuit - Google Patents

Abstract

PURPOSE:To prevent the inflow current into a power supply or ground even when voltage is impressed to an output terminal at the OFF of a unit by connecting a diode between the back gate of a PMOS transistor(TR) and the power supply. CONSTITUTION:Although the back gate 9 of the open drain type PMOS TR 1 is connected to the power supply 4 in a normal state, the state is equivalent to the connection of a parasitic diode 3 in structure. When voltage is impressed to the output terminal 4 in the OFF state of the power supply 4, a current is allowed to flow into the power supply 4 through the diode 3. Since the diode 2 is connected between the back gate 9 and the power supply 4 so that its anode is turned to the power supply side however, a diode 2 becomes a reverse bias state and no current flows into the power supply 4. Thereby even if the power supply 4 is turned off, the generation of bad influence upon another apparatus can be prevented because no current flows from the output terminal 6 into the other appartus through the power supply 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an open drain type output circuit.

[0002]

2. Description of the Related Art FIG. 5 shows an open drain type output circuit using a conventional PMOS transistor. In the figure, 1 is a PMOS transistor, the source of which is connected to the power supply terminal 4. Reference numeral 3 denotes a parasitic diode of the PMOS transistor 1, which is parasitic in a direction in which a current flows from the drain of the PMOS transistor 1 to the back gate side. Further, 4 is a power supply terminal, 5 is a PMOS transistor 1
, 6 is an output terminal from which a signal of this output circuit is output, and 9 is a back gate of the PMOS transistor 1.

FIG. 6 shows an open drain type output circuit using a conventional NMOS transistor. In the figure, 7 is an NMOS transistor, the source of which is connected to the ground 8. 3 is a parasitic diode of the NMOS transistor 7,
Parasitic in the direction of current flow from the drain to the back gate side. Further, 8 is a ground, 5 is a gate of the NMOS transistor 7, 6 is an output terminal for outputting a signal of this output circuit, and 9 is a back gate of the NMOS transistor 7.

Next, regarding the operation, a LAN (Local Area)
(Network) A case of being used as an output circuit of a signal to a transmission line will be described as an example.

FIG. 3 schematically shows a general bus type LAN transmission line and devices connected thereto. The output circuit thereof is an open drain type circuit using PMOS transistors shown in FIG. Used. In the figure, 61 is a bus line for a plurality of devices to exchange data, 70 is a terminating resistor, 31 and 32 are peripheral devices such as data terminals and printers, and 11 and 12 are data of the peripheral devices 31 and 32. Drivers 21 and 22 for outputting to the bus line 61 are controllers for controlling the drivers 11 and 12. 51 and 52 are peripheral devices 3
1, 32, controllers 21, 22 and driver 1
Units 1 and 12, 41 and 42 are units 5
1, 52 power supplies.

Next, the operation will be described. In a LAN transmission line in which a plurality of units 51 and 52 are connected to a bus line, when an open drain output PMOS transistor is used for the output of the drivers 11 and 12, a current flows when the transistor turns on, and the termination resistor 70 causes the bus line. 61 becomes "H". When the transistor is turned off, the bus line becomes "L" because it is pulled down by the terminating resistor 70. Therefore, the controllers 21, 2
By turning on / off the drivers 11 and 12 by 2, the bus line can be driven and data can be mutually sent between the peripheral devices.

FIG. 4 schematically shows a general bus type LAN transmission line and devices connected to it.
The output circuit is an open drain type circuit using the NMOS transistor shown in FIG. In the figure, 61 is a bus line for a plurality of devices to exchange data, 170 is its pull-up resistor, 4
3 is a power supply for pulling up the bus line 61, 31, 32
Are peripheral devices such as data terminals and printers, 11 and 12 are drivers for outputting data of the peripheral devices 31 and 32 to the bus line 61, and 21 and 22 are controllers for controlling the drivers 11 and 12. Reference numerals 51 and 52 are units including peripheral devices 31 and 32, controllers 21 and 22 and drivers 11 and 12, and 141 and 142 are grounds of the units 51 and 52.

Next, the operation will be described. Unit 5
In a LAN transmission line in which a plurality of bus lines 1 and 52 are connected, when an NMOS transistor having an open drain output is used for the output of the drivers 11 and 12, a current flows when the transistor is turned on, and a pull-up resistor 170 pulls up. The bus line 61 which has been operated becomes "L". When the transistor is turned off, the bus line 61 remains pulled up by the pull-up resistor 170, so that the bus line becomes "H". Therefore, by turning the drivers 11 and 12 on and off by the controllers 21 and 22, the bus lines can be driven and data can be mutually sent between the peripheral devices.

[0009]

Since the conventional device is constructed as described above, when a voltage is applied to the output terminal when the power supply of the unit is off, the parasitic diode of the transistor is used to connect the power supply side of the driver and the ground. Current may flow to the side, which may adversely affect the controller and peripheral devices.

The present invention has been made in order to solve the above problems, and can prevent a current from flowing into the power supply or the ground even when a voltage is applied to the output terminal when the power supply of the unit is turned off. The purpose is to obtain an output circuit.

[0011]

According to an output circuit of the present invention, a source and a back gate are connected to a power supply and an open drain output PMOS transistor whose drain serves as an output is provided with an anode between the back gate and the power supply. The diode is connected to the power supply side.

Further, in the output circuit according to the present invention, the source and the back gate are connected to the ground, and the drain is an open drain output NMOS transistor, and the anode is on the ground side between the back gate and the ground. The diode is connected like this.

[0013]

With the semiconductor device according to the present invention configured as described above, even if a voltage is applied to the output terminal, the diode connected between the back gate and the power supply is in a reverse bias state, so that a current flows into the power supply. Prevent.

Further, since the semiconductor device according to the present invention is configured as described above, the diode connected between the back gate and the ground is in a reverse bias state even when a voltage is applied to the output terminal, so that a current flows to the ground. Prevent it from flowing.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an output circuit according to an embodiment of the present invention.
In the figure, 1 is an open drain type PMOS transistor, 2 is a diode inserted between the source and back gate of the PMOS transistor 1, the anode is connected to the source and the cathode is connected to the back gate, and 3 is P
A parasitic diode 4 that parasitizes a current from the drain of the MOS transistor 1 toward the back gate, 4 is a power source, 5 is a gate of the PMOS transistor 1, 6 is an output terminal, and 9 is a back gate of the PMOS transistor 1. The diode 2 may be formed in the same wafer as the transistor 1 or may be realized by an individual element.

Next, the operation will be described. As described in the conventional example, when an open drain output PMOS transistor is used for a driver that drives a bus line such as a LAN transmission line, a plurality of units are connected.
Each unit is operating independently and some are powered on, others are off.

The back gate of the PMOS transistor 1 is normally connected to the power supply 4, which is equivalent to the diode 3 which is structurally parasitic. Therefore, when a voltage is applied to the output terminal 6, a current flows toward the power supply through the parasitic diode 3 when the power supply is off.

However, in this embodiment, since the diode 2 is connected between the back gate 9 and the power source 4 so that the anode is on the power source side, the diode 2 is in a reverse bias state and current flows into the power source. There is no such thing.

Therefore, even if the power is turned off, the current does not flow from the output terminal to the other equipment through the power supply, so that the adverse effect on the other equipment can be prevented.

Although the open drain output circuit using the PMOS transistor is shown in the above embodiment, the same concept can be applied to the open drain output circuit using the NMOS transistor as shown in FIG. The same effect can be obtained.

In FIG. 2, reference numeral 7 is an open drain type NMOS transistor, and 2 is an NMOS transistor 7.
, A parasitic diode which is inserted between the back gate and the ground so that the anode is on the ground side, 3 is a parasitic diode which causes a current to flow from the output terminal to the back gate of the NMOS transistor 7, and 5 is the NMOS transistor 7. , 8 is ground, 6 is an output terminal for taking out an output signal of this output circuit, and 9 is a back gate of the NMOS transistor 7. The transistor 7
The diode 2 and the diode 2 may be formed in the same wafer, or may be realized by separate elements.

The back gate of the NMOS transistor 7 is normally connected to the ground 8, which is equivalent to the diode 3 which is structurally parasitic. Therefore, when a voltage is applied to the output terminal 6, a current flows toward the ground through the parasitic diode 3 when the power supply is off.

However, in this embodiment, the diode 2 is connected between the back gate 9 and the ground 8 so that the anode is on the ground side.
Is reverse biased, and no current flows into the ground.

Therefore, even if the power is turned off, the current does not flow from the output terminal to the other equipment through the ground, so that the adverse effect on the other equipment can be prevented.

[0025]

As described above, according to the output circuit of the present invention, the source and the back gate are connected to the power supply, and the drain is an open drain output PMOS transistor. Since the diode is connected so that the anode is on the power supply side, even if the power is turned off, current does not flow from the output terminal to other equipment through the power supply, so it is possible to prevent adverse effects on other equipment. There is.

According to the output circuit of the present invention,
Since the source and back gate are connected to the ground, and the drain is an output, an open drain output NMOS transistor is connected between the back gate and ground so that the anode is on the ground side. Even if it is turned off, the current does not flow from the output terminal to the other device through the ground, so that it is possible to prevent the other device from being adversely affected.

[Brief description of drawings]

FIG. 1 is a diagram showing an output circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing an output circuit according to a second embodiment of the present invention.

FIG. 3 is a diagram for explaining an application example of the output circuit of FIG.

FIG. 4 is a diagram for explaining an application example of the output circuit of FIG.

FIG. 5 is a diagram showing an example of a conventional output circuit.

FIG. 6 is a diagram showing another example of a conventional output circuit.

[Explanation of symbols]

 1 PMOS transistor 2 Diode 3 Parasitic diode 4 Power supply 5 Gate 6 Output terminal 7 NMOS transistor 8 Ground 9 Back gate 11, 12 Driver 21, 22 Controller 31, 32 Peripheral device 41, 42, 43 Power supply 51, 52 Unit 61 Bus line 70 Termination resistance 170 Pull-up resistance

Claims (2)

[Claims] 1. An open drain output PMOS transistor having a source and a back gate connected to a first power supply and having a drain as an output, and an anode between the back gate of the PMOS transistor and the first power supply is a first power supply. 1. An output circuit comprising: a diode connected so as to be on the power supply side of No. 1. 2. An open-drain output NMOS transistor having a source and a back gate connected to a second power supply and a drain serving as an output; and an anode between the back gate of the NMOS transistor and the second power supply. 2. An output circuit comprising a diode connected so as to be on the side of the power supply of 2.