JPH08107341A - Input buffer - Google Patents

Abstract

PURPOSE: To allow a buffer to cope with over a wide range of power supply voltage by operating selectively plural input buffer sections whose power supply operating voltage differs from each other. CONSTITUTION: The input buffer 110 is made up of an input buffer circuit 10 and a power supply voltage detection circuit 20. A 3V exclusive input buffer section 1 and a 5V exclusive use input buffer section 2 are provided to an input signal line 3 of the input buffer circuit 10. Either of the input buffer sections 1, 2 is operated selectively depending on a power supply voltage detected by the power supply voltage detection circuit 20. For example, when an input buffer section selection signal 31 is at an H level, the 3V exclusive use input buffer section 1 is inactive and the 5V exclusive use input buffer section 3 is selected and actuated. The input buffer is realized over a wider range of operating power supply voltage and the general-purpose input buffer requiring no replacement is obtained even when the power supply voltage is revised.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input buffer, and more particularly to an input buffer which operates with a wide range of power supply voltages.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing how an input buffer is generally used. Input buffer 100
Is connected to an input stage of an internal circuit 200 including, for example, a microcomputer, a memory, a decoder, etc., receives an input signal line 3 from the outside, and an output signal line 4 thereof is connected to the internal circuit 200, The internal circuit 200 is protected from an abnormal signal such as an impact voltage or an impact current from the outside.

The input buffer 100 comprises an input buffer section provided for each input signal line, and one input buffer section is a P-channel transistor (hereinafter referred to as a Pch transistor, for example) connected between a power source and a ground. )) And an N-channel transistor (hereinafter referred to as Nch transistor).

[0004]

The conventional input buffer is constructed as described above. By the way, in order to prolong the life of a battery of a battery-driven electronic device such as a portable electronic device, recently, an operating power supply voltage has been frequently lowered. Further, such an electronic device is required to operate with an existing power supply voltage, and it is inevitably required to operate with a wide range of power supply voltage. At this time, the level of the input buffer changes depending on the operating power supply voltage.

However, for example, the power supply voltage Vcc = 5V
There is a case in which it is desired to receive the same TTL level even when Vcc = 3V (meaning that a signal is supplied to the internal circuit) when Vcc = 3V. However, since the threshold value of this input level is usually determined by the ratio of the resistance value when the transistor is ON, it is not possible to set it to the TTL level with Vcc of both 5V and 3V (VIH = 2.0V, VIL = 0.
8V) It was difficult with one input buffer.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an input buffer that can handle a wide range of power supply voltages.

[0007]

In view of the above object, the first aspect of the present invention is to provide two or more input buffer sections having different operating power supply voltage ranges with respect to one input signal line. Input buffer means, power supply voltage detection means for detecting a power supply voltage, and input buffer section selecting means for selectively operating any of the input buffer sections according to the power supply voltage. In the buffer.

According to a second aspect of the present invention, an input is provided for one input signal line and a corresponding operating power supply voltage changing unit for changing a corresponding operating power supply voltage of the input buffer unit. The input buffer includes buffer means, power supply voltage detection means for detecting a power supply voltage, and corresponding operating power supply voltage changing portion control means for controlling the corresponding operating power supply voltage changing portion according to the power supply voltage.

[0009]

According to the first aspect of the present invention, two or more input buffer sections having different operating power supply voltage ranges are provided for one input signal line, and the input buffer section of the input buffer section is provided in accordance with the detected power supply voltage. Made the corresponding ones selectively operable.

In the second aspect of the present invention, one input buffer section is provided for one input signal line, and a corresponding operating power supply voltage changing section for changing the corresponding operating power supply voltage of the input buffer section is provided and detected. The corresponding operating power supply voltage changing unit is controlled according to the supplied power supply voltage.

[0011]

Embodiments of the present invention will be described below. Example 1. FIG. 1 is a diagram showing the structure of an input buffer according to an embodiment of the present invention. In FIG. 1, the input buffer 110 includes an input buffer circuit 10 and a power supply voltage detection circuit 2.
Consists of zero.

In the input buffer circuit 10, 1 is 3V
Dedicated input buffer section, 2 is a 5V dedicated input buffer section, 4
Is an input signal line, and 5 is an output signal line. Note that FIG. 1 shows the configuration for one input signal line 3, and when there are a plurality of input signal lines 3, a 3V dedicated input buffer unit 1 and a 5V dedicated input buffer unit are provided for each input signal line, respectively. Two are provided.

In the power supply voltage detection circuit 20, 2
Reference numerals 1a and 21b are dividing resistors, 22 is a reference voltage source, and 23 is a comparator. Further, 30 is a power supply (Vcc), and 31 is an input buffer section selection signal line. Even if there are a plurality of input signal lines 3, one of these may be provided in common.

Input buffer units 1 and 5 dedicated to 3V are used.
The V-only input buffer section 2 constitutes an input buffer means,
The dividing resistor 21 constitutes a power supply voltage detecting means, and the reference voltage source 22, the comparator 23 and the input buffer section selecting signal line 31 constitute an input buffer section selecting means.

Next, the operation will be described. The input buffer unit 1 dedicated to 3V has Vcc = 3V, VIH = 2.0V, VIL =
In the input buffer unit that determines H level and L level at 0.8 V, the 5 V dedicated input buffer unit 2 has a power supply voltage Vcc =
It is 5V. The reference voltage source 22 is, for example, 1.25V,
Among the dividing resistors, the upper dividing resistor 21a is 110 kΩ and the lower dividing resistor 21b is 50 kΩ.

At this time, when the operating power supply voltage Vcc = 5.0V, the output from the connection point of the dividing resistors 21a and 21b is about 1.56V, which is larger than 1.25V of the reference voltage source 22, and the output of the comparator 23. Becomes H level.

When the input buffer section selection signal 31 is at the H level, the 3V-dedicated input buffer section 1 is in the non-operating state, and the output is in the high impedance state "Hz". Then, the 5V-dedicated input buffer unit 2 is selected and put into an operating state, and the TTL level input of the operating power supply voltage 5V (input from the output signal line 4 to the internal circuit) can be realized.

Next, when the operating power supply voltage Vcc = 3.0V, the output of the dividing resistors 21a and 21b is about 0.94V, which is smaller than 1.25V of the reference voltage source 22, and the output of the comparator 23 becomes L level. Become.

When the input buffer section selection signal 31 is at the L level, the 5V-dedicated input buffer section 2 is in the non-operating state, and the output is in the high impedance state "Hz". Then, the 3V-dedicated input buffer unit 1 is selected and put into an operating state, and TTL level input of the operating power supply voltage 3V (input from the output signal line 4 to the internal circuit) can be realized.

In the above embodiment, the case where the operating power supply voltage Vcc is 5 V and 3 V has been described, but the present invention is not limited to this, and other operating power supply voltages may be used. Also, the operating power supply voltage is not limited to two types, and three or more types can be implemented by adding an input buffer unit and the like.

As described above, according to this embodiment, by providing a plurality of input buffer sections having different operating power supply voltages for one input signal line, an input buffer capable of handling a wide range of operating power supply voltages is provided. Can be realized.

Example 2. FIG. 2 is a diagram showing the structure of an input buffer according to another embodiment of the present invention. In FIG. 2, the input buffer 120 includes an input buffer circuit 10a and a power supply voltage detection circuit 20.

In the input buffer circuit 10a, 3 is an input signal line, 4 is an output signal line, 11 and 12 are analog switches, 13 is a pull-up resistor, 14 is a pull-down resistor,
Reference numeral 15 is a Pch transistor, and 16 is an Nch transistor. Reference numeral 17 denotes a conventional inverter portion, which includes a Pch transistor 17a and an Nch transistor 17b.

Reference numeral 18 denotes a pre-stage input inverter provided in the present invention together with the analog switches 11 and 12, the pull-up resistor 13, the pull-down resistor 14 and the transistors 15 and 16, and comprises a Pch transistor 18a and an Nch transistor 18b.

Regarding the power supply voltage detection circuit 20,
Since it is basically the same as that of the first embodiment shown in FIG. 1,
Description is omitted. However, the output signal line from the comparator 23 is the corresponding operating power supply voltage control signal line 32.

The input buffer circuit 10a constitutes the input buffer means, of which the latter-stage input inverter 17 is included.
Constitutes an input buffer section, and analog switches 11 and 1
2, the pull-up resistor 13, the pull-down resistor 14, the transistors 15 and 16, and the front stage inverter 18 constitute a corresponding operating power supply voltage changing unit. In addition, the division resistor 21
a and 21b constitute a power supply voltage detecting means, and a reference voltage source 2
2, the comparator 23 and the corresponding operating power supply voltage control signal line 32 constitute the corresponding operating power supply voltage changing unit control means.

Next, the operation will be described. Since the operation of the power supply voltage detection circuit 20 is the same as that of the first embodiment, the description will be omitted. When the power supply voltage Vcc = 5.0V, the corresponding operation power supply voltage control signal 32 is set to the H level. Then, the analog switch 12 is turned on and the analog switch 11 is turned off. The Pch transistor 15 is always turned off by the pull-up resistor 13, and the Nch transistor is turned on / off according to the input signal 3. Therefore, if the size of the Nch transistor is determined so that the threshold value at this time is about 1.5 V, the TTL level input of the operating power supply voltage Vcc = 5.0 V (from the output signal line 4 to the internal circuit) Input) can be realized.

Next, when the power supply voltage Vcc = 3.0V, the corresponding operation power supply voltage control signal 32 is set to the L level. Then, the analog switch 11 turns on and the analog switch 12
Turns off. The Pch transistor 16 is always turned off by the pull-down resistor 14, and the Pch transistor is turned on / off according to the input signal 3. Therefore, set Pch so that the threshold value at this time is about 1.5V.
If the size of the transistor is determined, the operating power supply voltage Vcc
= 3.0V TTL level input (input from the output signal line 4 to the internal circuit) can be realized.

Needless to say, the voltage value and the number of types of the operating power supply voltage Vcc are not limited to those in the above embodiment.

As described above, according to this embodiment, an input buffer that can handle a wide range of operating power supply voltages can be easily realized by simply adding a simple circuit including a transistor to one input buffer section.

[0031]

As described above, according to the first aspect of the present invention, two or more input buffer sections having different operating power supply voltage ranges are provided for one input signal line, and detection is performed. Since the corresponding ones of the above input buffer units are made selectively operable according to the power supply voltage,
It is possible to realize an input buffer with a wide range of operating power supply voltage, and to provide a versatile input buffer that does not require replacement of the input buffer even when the power supply voltage is changed.

According to the second aspect of the present invention, 1
One input buffer unit and a corresponding operating power supply voltage changing unit for changing the corresponding operating power supply voltage of the input buffer unit are provided for each input signal line, and the corresponding operating power supply voltage changing unit of the corresponding operating power supply voltage changing unit is provided according to the detected power supply voltage. Since the control is performed, an input buffer with a wide operating power supply voltage can be easily realized by simply adding a simple circuit including a transistor to one input buffer unit, and the input buffer can be used even if the power supply voltage is changed. This has the effect of providing a versatile and inexpensive input buffer that does not need to be replaced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an input buffer according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an input buffer according to another embodiment of the present invention.

FIG. 3 is a diagram showing a general usage state of an input buffer.

[Explanation of symbols]

1 3V dedicated input buffer section, 25V dedicated input buffer section, 3 input signal line, 4 output signal line, 10 input buffer circuit, 20 power supply voltage detection circuit, 21a, 21b
Dividing resistor, 22 reference voltage source, 23 comparator,
30 power supply, 31 input buffer selection signal line, 32
Corresponding operation power supply voltage control signal line, 110, 120 input buffer.

Claims (2)

[Claims] 1. An input buffer means comprising two or more input buffer sections each having a different operating power supply voltage range for one input signal line, a power supply voltage detecting means for detecting a power supply voltage, and the power supply. An input buffer section selecting means for selectively setting one of the input buffer sections in an operable state according to a voltage; 2. An input buffer unit for one input signal line, and an input buffer unit each provided with a corresponding operation power supply voltage changing unit for changing a corresponding operation power supply voltage of the input buffer unit, and a power supply voltage. An input buffer comprising: a power supply voltage detection unit for detecting; and a corresponding operation power supply voltage change unit control unit for controlling the corresponding operation power supply voltage change unit according to the power supply voltage.