JPH04107007A - Semiconductor device - Google Patents

Abstract

PURPOSE:To reduce the power consumption of an output drive circuit by setting the capability of output current to an optimum value in accordance with an external connected circuit. CONSTITUTION:An output drive circuit 5 consists of transistors TRs Tr1 to Tr4 and a control logic gate. When a signal S select is in the low level, TRs Tr3 and Tr4 are always turned off, and the output is driven only by TRs Tr1 and Tr2. When the signal S select is in the high level, the output is driven by Tr1+Tr3 and Tr2+Tr4 to increase the capability of the output current. If the output current required for an external circuit 9 is obtained by TRs Tr1 and Tr2, the signal S select is set to the low level to always turn off TRs Tr3 and Tr4, and the through current is reduced. If a large output current is required, the signal S select is set to the high level. Thus, the capability of the output current of the output drive circuit is optimized to reduce the power consumption.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to reducing power consumption of semiconductor devices.

[Conventional technology]

When making a general-purpose IC, there are a variety of externally connected circuits, and the output drive circuit is designed to have a fairly large output current capacity with a margin to accommodate many of them.

[Problem to be solved by the invention]

Generally, if the output current capacity of an output drive circuit is increased, the power consumption of the output drive circuit increases. However, in conventional ICs, the output current capacity of one output driver circuit is designed to be large, so when used for applications where the output current is small, the power consumption of the output drive circuit is higher than necessary. Therefore, the present invention is intended to solve such problems, and its purpose is to reduce the power consumption of a semiconductor device.

[Means to solve the problem]

A semiconductor device of the present invention is a semiconductor device having at least an output drive circuit, wherein the output drive circuit is configured to vary an output current capability, and includes a control means for setting the output current capability of the output drive circuit. It is characterized by

[Effect]

The output current capacity of the output drive circuit is set by the control means so that the output current value is the minimum value necessary for the connected external circuit. Power consumption can be reduced by optimizing the output current capability of the output drive circuit.

【Example】

FIG. 1 is a circuit diagram around an output drive of an embodiment of the semiconductor device of the present invention. FIG. 1 is an example of an output drive circuit composed of an inverter having a CMOS structure. A conventional example of an output drive circuit having a similar configuration is shown in FIG. First, the conventional example shown in FIG. 2 will be explained. In Figure 2, 1
is the output drive circuit, 2 is the output terminal, 3 is the internal circuit, 4
is an external circuit connected to the outside. In Figure 2, the output drive circuit is a MoS transistor T
It is composed of rl and Tr2. In an inverter with a 0MO3 structure, the input signal Sin changes from °H' to L'' or °L'
When changing from IHI to IHI, there is a state in which Trl and Tr2 are turned on, and a through current flows. In addition, the through current is
It is proportional to the current flowing ability of Trl and Tr2, and further proportional to the output current ability. That is, if the output current capacity is increased more than necessary, the through current will also increase more than necessary. The present invention adjusts the output current of the output drive circuit to the necessary minimum value according to the external circuit, so that the above-mentioned through current can be minimized and power consumption can be reduced. In FIG. 1, 5 is an output drive circuit configured to be able to vary the output current capacity, 6 is an output terminal, 7 is a selection terminal that determines the output current capacity of the output drive circuit 5;
8 is an internal circuit, and 9 is an external circuit connected to the outside. This semiconductor device refers to numbers 5 to 8. The output drive circuit 4 includes transistors Tri, Tr2, Tr3, and Tr.
4 and a logic gate for control. The selection terminal 6 is. The output current capability of the output drive circuit is determined by setting it to H or L. The signal from the internal circuit to the output drive circuit is Sin, the output signal from the output terminal is 5out,
The signal from the selection terminal is 5select, and the on/off state of each transistor is shown in FIG. From Figure 3,
When 5select is IL+, Tr3 and Tr4 are always off, and only Tri and Tr2 drive the output. 5
When select is +h', Trl+Tr3, Tr2+
The output is driven by Tr4, increasing the output current capacity. The output current required for the external circuit 9 is Tri and T.
When r2 is obtained, by setting 5select to Ill, it is possible to always turn off Tr3 and Tr4 and reduce the through current. Also, if a large output current is required, 5select may be set to H". Figure 4 shows another embodiment of the present invention. In Figure 4, 10 indicates a relatively small output current. Clocked inverter, 11 is a clocked inverter with relatively large output current,
12 is an internal circuit, 13 is an output terminal, 14 is an external circuit, 1
5 is a selection terminal. When the output current required by the external circuit 14 is small, the selection terminal 15 is set to "L" to operate the clocked inverter 10, which has a relatively small output current, to drive the output.When the output current required for the external circuit 14 is large, , select terminal 15 to H
Clocked inverter 11 with a relatively large output current
operate and drive the output. A specific example of the application of the present invention is an application to a portable computer equipped with a liquid crystal display as standard equipment and also capable of connecting a CRT. FIG. 5 is a block diagram when the present invention is applied to a portable computer. In FIG. 5, 20 is a CPU;
21 is a memory, 22 is an input/output circuit, 23 is a CRT display circuit, 24 is a signal conversion circuit, 25 is a liquid crystal display device, and 26 is a CRT display circuit.
An RT connection connector, 27 is a CRT, and 28 is a CRT connection detection means. The CPU 20, memory 21, and input/output circuit 22 are basic components of a general computer. A feature of this computer is the display section, which is equipped with a liquid crystal display as standard and can also be connected to a CRT. First, a CRT display signal is created by the CRT display signal creation device 23. The signal conversion circuit 24 converts the CRT display signal into a liquid crystal display signal, and the liquid crystal display device 25 displays the signal. Also, CRT
The CRT display signal, which is the output of the display signal generation device 23, is output to the outside via the CRT connection connector 26.
By connecting the CRT 27 to this connector 26, the CR
T display becomes possible. Now, if we pay attention to the output of the CR1 display signal generation device 23, the output load will be different depending on whether the CRT 27 is connected or not, and the required output current capacity will also be different. Therefore, the circuit of FIG. 1 according to the present invention is applied to the output drive circuit of the CR1 display signal generating device 23, and a selection terminal is added. The CRT connection detection means 28 is configured to output a 'H' signal when the CRT 27 is connected, and to output a +L+ signal in other cases, and connects the output signal to the selection terminal of the CR1 display signal generation device 23. The CRT connection detector 823 may be a simple switch or may be switched by the user. CRT
27 is not connected, the CRT connection detection means is “L”.
. Output a signal. Then, the CR1 display signal generation device 23
The selection terminal becomes L°, lowering the output current capability of the output drive circuit and reducing power consumption. When the CRT 27 is connected, the CRT connection detection means outputs a °H' signal. Then, the selection terminal of the CR1 display signal generating device 23 becomes .degree.H', and by increasing the output current capacity of the output driver 1 circuit, it is possible to cope with an increase in the output load when the CRT is connected. Although the present invention has been described above using a CMO6 structure semiconductor device as an example, it is of course applicable to semiconductor devices having other structures. Further, the configuration of the output drive circuit can also be applied to one using a buffer or an operational amplifier. In the embodiment, an example was shown in which the output current capacity can be varied in two stages, but it can also be applied to variable in multiple stages. In a specific example,
As a system, it can be applied to the output drive circuit of signals output from expansion connectors of computers, etc., or as a general-purpose IC.
It can also be used to optimize the general output drive circuit according to external circuits.

【Effect of the invention】

Since the semiconductor device of the present invention can set the output current capacity to an optimal value depending on the circuit connected to the outside, it is possible to reduce the amount of power consumed by the output drive circuit. Further, it can be realized by only slightly modifying or changing the conventional circuit, and can be applied to all output drive circuits.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram around an output drive of an embodiment of the semiconductor device of the present invention. FIG. 2 is a circuit diagram around the output drive of a conventional semiconductor device. FIG. 3 is a state diagram showing the operation of FIG. 1. FIG. 4 is a circuit diagram around the output drive of another embodiment of the semiconductor device of the present invention. FIG. 5 is a block diagram when the present invention is applied to a portable computer. , an output drive circuit 60 configured to be able to vary output terminals, internal circuits, external circuits, and output current capabilities. Output terminal selection terminal Internal circuit External circuit Clocked inverter 111 with relatively low output current. Clocked inverter with relatively large output current Internal circuit output terminal External circuit selection terminal PU Memory, input/output circuit CRT display circuit, signal conversion circuit, liquid crystal display CRT connection connector RT CRT connection detection means 12° 13° 14° 15° 20゜21゜22゜23゜24゜25゜26゜27゜28゜Figure 3Figure 4T

Claims (1)

[Scope of Claims] A semiconductor device having at least an output drive circuit: (1) The output drive circuit is configured to vary the output current capacity, and a control means for setting the output current capacity of the output drive circuit. A semiconductor device characterized by having: