JPH02162821A - Chattering elimination circuit - Google Patents

Abstract

PURPOSE:To reduce the number of components by charging and discharging a capacitor from a constant current source according to an input signal and comparing a voltage across the capacitor with a reference voltage so as to obtain an output. CONSTITUTION:An output of a comparator 5 changes from a low to a high level at a chattering when an input signal changes from a high level to a low level, a transistor(TR) 14 is turned from ON to OFF and a TR 15 is turned from OFF to ON and the capacitor 9 is discharged by a constant current source 9 and the voltage across the capacitor 9 is decreased. Since the input signal is inverted at the chattering part in a short time, the capacitor 9 is charged by a constant current source 7 and the capacitor voltage is increased again. Thus, the voltage across the capacitor 9 is always higher than a voltage at a point B being a reference voltage and the output 4 of the comparator 6 is kept to a high level. Thus, since a counter detecting the chattering width is not in use, the circuit is integrated with a few components.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to integrated circuits, and more particularly to chattering removal circuits.

[Prior Art] Conventional chattering removal circuits are either configured with an integrating circuit using a capacitor and a resistor outside the integrated circuit, or configured to use a clock counter inside the integrated circuit to determine whether the input signal has a pulse width of a certain time or more. It became.

[Problem to be solved by the invention, M] In the conventional chattering removal circuit described above, when an integrating circuit is configured using a capacitor and a resistor outside the integrated circuit, the capacitance value of the capacitor increases and the configuration remains the same. However, the disadvantage is that it cannot be built into an integrated circuit.

In addition, when making decisions based on pulse width using a clock counter inside an integrated circuit, a CR oscillation circuit or crystal oscillation circuit and a counter are required for the clock, and especially in bipolar type integrated circuits that do not use a clock, the device The disadvantage is that the number increases significantly.

[Means for Solving the Problems] The chattering removal circuit of the present invention includes: a capacitor; a first comparator that shapes the waveform of an input signal; and an output of the first comparator when the input signal is at a first logic level. A capacitor charging constant current circuit that operates to charge the capacitor, a capacitor discharge constant current circuit that operates based on the output of the first comparator when the input signal is at the second logic level and discharges the capacitor, and a capacitor maximum voltage. and a reference voltage source that generates a voltage at an intermediate level between the minimum voltage and the minimum voltage as a reference voltage, and a second comparator that compares the voltage of the capacitor with the reference voltage.

[Operation] When the input signal is at the first logic level, the capacitor is charged by the constant current circuit for charging the capacitor, and since the voltage thereof is higher than the reference voltage, the output of the second comparator becomes high level or low level.

In the chattering part when the input signal switches from the first logic level to the second logic level, the capacitor is discharged by the constant current circuit for discharging the capacitor, and the voltage of the capacitor decreases. Since the voltage is inverted to a high level, the voltage of the capacitor is charged again without falling below the reference voltage, and the voltage of the capacitor rises.

Therefore, in the chattering section, the voltage of the capacitor is always higher than the reference voltage, so the output of the second comparator is kept at high level or low level.

When the chattering part ends and the input signal becomes low level, the capacitor continues to be discharged by the capacitor discharge constant current circuit, and when the voltage of the capacitor drops below the reference voltage, the output of the second comparator changes from high level (low level). Inverted to low level (high level).

The same is true when the input signal is inverted from the second logic level to the first logic level.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the chattering removal circuit of the present invention, and FIG. 2 is a waveform diagram of each part of FIG. 1.

This embodiment includes a capacitor 9, a constant current source 7.8 for charging and discharging the capacitor, a transistor 14.15 for switching constant current charging and discharging, and resistors 10 to 13 for a reference voltage source.
It is composed of comparators 5 and 6.

Next, the operation of this embodiment is as follows: the input signal shown in FIG.
The case where the voltage is applied will be explained below.

The comparator 5 is a comparator for waveform shaping, and the output of the comparator 5 is a signal obtained by inverting the input signal. When the input signal is at a high level, the output of the comparator 5 is at a low level. At this time, the transistor 14 is on and the transistor 15 is off, so the capacitor 9 is being charged by the constant current source 7. Therefore, the capacitor voltage (potential at point A) is higher than the reference voltage (potential at point B) generated by the resistor 12.13, and the output of the comparator 6 goes to a high level.

Next, in the chattering portion when the input signal switches from high level to low level, the input signal changes from high level to low level, and the output of the comparator 5 changes from low level to high level. Therefore, the transistor 14 changes from on to off, and the transistor 15 changes from off to on.
The capacitor 9 is discharged by the constant current source 8, and the voltage of the capacitor 9 decreases as shown in the waveform at point A in FIG. However, in the chattering section, the input signal is reversed between high and low levels in a short time, so the capacitor voltage is
Before the voltage drops to the reference voltage at point B according to 2.13,
The input signal is inverted from low level to high level, the output of comparator 5 goes from high level to low level, transistor 14 goes from off to on, transistor 15 goes from on to off, capacitor 9 is charged by constant current source 7, and the capacitor voltage increases. will rise again. Therefore, in the chattering section, the voltage of the capacitor 9 is always higher than the voltage at point B, which is the reference voltage provided by the resistor 12.13, as shown in FIG. 2, so the output 4 of the comparator 6 remains at a high level.

Next, when the chattering part ends and the input signal becomes low level, the output of comparator 5 becomes high level,
The transistor 14 is turned off, the transistor 15 is turned on, and the capacitor 9 continues to be discharged by the constant current source 8. When the voltage of the capacitor 9 decreases to the reference voltage at point B, the output of the comparator 6 is inverted from high level to low level. Chattering can be removed as shown in Figure 2.

The same applies when the input signal is inverted from low level to high level. Capacitor 9 that can be built into an integrated circuit
The capacitance value is several 109 F, and the capacitor capacitance value is determined by the pulse width of the chattering part, the current value of constant current #7.8, and the potential at point B of the reference voltage. Constant current source 7.8
When the current value is 2 and the potential at point B of the reference voltage is 8, the capacitance gk of the capacitor 9 is determined by the pulse width T of the chattering portion. Since the pulse width of the chattering part is usually several ms, T=IOms, A=lOnA, Va=
If it is 2.5V, C=409F, which is a value that can be easily created in an integrated circuit.

FIG. 3 is a circuit diagram of a second embodiment of the chattering removal circuit of the present invention.

In this embodiment, switching between charging and discharging the capacitor 9 is performed only by the transistor 15.

When the transistor 15 is off, the capacitor 9 is charged by the constant current source 7, and when the transistor 15 is on, the capacitor 9 is discharged by the constant current source 8. By setting the current value of constant current source 8 to twice that of constant current source 7, the first
Chattering can be removed in the same way as in the embodiment.

This embodiment has the advantage that the number of elements can be further reduced compared to the first embodiment.

Note that the capacitor 9 may be charged when the input signal is at a low level and discharged when the input signal is at a high level.
Alternatively, the reference voltage at point B may be input to the non-inverting input terminal of the comparator 6, and the voltage of the capacitor 9 may be input to the inverting input terminal.

[Effects of the Invention] As explained above, the present invention charges and discharges a capacitor according to an input signal using a constant current source, compares the voltage of the capacitor with a reference voltage, and outputs the result. Since the present invention does not require the addition of a capacitor, nor does it use an oscillation circuit for the clock, a counter for detecting the chattering width, etc., the chattering removal circuit can be integrated with a small number of elements.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a first embodiment of the chattering elimination circuit of the present invention, FIG. 2 is a waveform diagram of each part of FIG. 1, and FIG. 3 is a circuit diagram of a second embodiment of the chattering elimination circuit of the present invention. It is a diagram. 1...Power supply, 2...-GND, 3...
Input, 4... Output, 5.6 - Comparator, 7.8... Constant current source, 9... Capacitor, 10
~13...Resistor, 14.15...Transistor.

Claims (1)

[Claims] 1. A capacitor, a first comparator that shapes the waveform of the input signal, and a capacitor charging device that operates based on the output of the first comparator when the input signal is at the first logic level to charge the capacitor. A constant current circuit, a constant current circuit for discharging a capacitor that is operated by the output of the first comparator when the input signal is at the second logic level, and discharging the capacitor; A chattering removal circuit that includes a reference voltage source that generates a reference voltage, and a second comparator that compares the voltage of a capacitor with the reference voltage.