JP2002009597A - Key input circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a key input circuit that can reduce its current consumption and allows a circuit network to read the switching. SOLUTION: This invention provides a technological concept such that an external disturbance by a switch operation is given to the circuit network in a state of holding a digital signal through positive feedback so as to allow the circuit network to capture a switch level. The output of the circuit is fixed to an L or H level while the positive feedback is active. When the switch state does not match the state level of the circuit network, a current momentarily flows to the switch, but positive feedback becomes soon active to converge the voltage level to the same level. Thus, the switch level can be read without the need for supplying a steady-state current to the switch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for inputting a key switch while reducing current consumption.

[0002]

2. Description of the Related Art Conventionally, in order to input the open / closed state of a switch, a current such as a pull-up resistor is always detected by a method of flowing the current. For example, if one side of the switch is connected to the power supply via a pull-up resistor and the other side of the switch is grounded,
The voltage on one side swings in the voltage range between the power supply and ground.

[0003]

However, in such a method, current always flows through the pull-up resistor when the switch is closed. Therefore, the present invention
An object of the present invention is to solve the problem of reducing current consumption by eliminating a steady current flowing through a switch.

[0004]

In order to solve this problem, a disturbance is caused by a switch operation on a network capable of holding a digital signal by applying positive feedback, and the level of the switch is taken into the network. It is a technical idea.

When the state of the switch and the state level of the circuit network do not match, a current flows through the switch for a moment, but positive feedback is immediately applied and the voltage converges to the same voltage level. As a result, the level of the switch can be read without a steady current flowing through the switch.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a basic configuration diagram of the present invention.

In FIG. 1, a switch 1 is a make switch having one contact and two contacts, one of which is connected to a power supply and the other is connected to ground. The inverter 2 as an input buffer simply inverts the signal. Transistors 4, 5
And the current limiting resistors 3 and 6 constitute an output driver with current limitation. The point of this output driver is that the current is limited, and the output driver is not a normal driver but also applies a positive feedback to the input side of the inverter 2. As a result, the input level of the inverter 2 is determined to be H / L even when the switch 1 is in the open state. Since positive feedback is applied, no current flows even if the switch is connected to either side. The current flows only momentarily only during the transitional period of switching.

As a target of the current limitation, it is preferable that the leakage current of the substrate on which this circuit is mounted is negligible and is as small as possible. As an embodiment,
It is limited to about 50 microamps.

A simple inverter receiving the output of the input buffer is a circuit for reading out the state of the switch, and is a circuit for cutting off the influence of the output load.

FIG. 2 shows a case where the reset signal sets the initial value of L. NA instead of inverter
Using the ND gate 8, the initial value is set to L when the reset signal is at L level.

FIG. 3 shows a case where the initial value of H is set by a reset signal. NO instead of inverter
The initial value is set to H when the reset signal is at L level using the R gate 9.

As described above, according to the embodiment of the present invention, the level of the switch 1 can be detected without passing a steady current through the resistor.

[0014]

As described above, the input circuit of the switch according to the present invention comprises: an input buffer for inputting a signal; an output driver having current limiting means for amplifying the output of the input buffer and limiting the current; Since the output side of the output driver is provided with a means for applying a positive feedback to the input side of the input buffer, the level of the switch can be detected without constantly flowing a current.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is a diagram when an initial value is set to L;

FIG. 3 is a diagram when an initial value is set to H;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switch 2 Input buffer 3 Current limiting resistor 4 Transistor 5 Transistor 6 Current limiting resistor 7 Output buffer 8 NAND gate 9 NOR gate

Claims (2)

[Claims] An input buffer for inputting a signal and current limiting means for amplifying the output of the input buffer and limiting the current so as to allow a current to flow by orders of magnitude less than the current driving capability of the input signal source. A key input circuit, comprising: an output driver provided with the output driver; and a means for applying a positive feedback from an output side of the output driver to an input side of the input buffer. 2. The input buffer according to claim 1, wherein the input buffer is NAN.
A key input circuit comprising a D gate or a NOR gate and having means for receiving a reset signal for setting an initial value.