Chattering eliminating apparatus including oscillation circuit using charging and discharging operations

1. A chattering eliminating apparatus comprising:

a coincidence circuit for receiving an input signal of said apparatus and an output signal of said apparatus to determine whether or not a level of the input signal of said apparatus is the same as a level of the output signal of said apparatus;

an oscillation circuit, connected to said coincidence circuit, for carrying out an oscillation operation only when the level of the input signal of said apparatus is not the same as the level of the output signal of said apparatus;

a counter, connected to said oscillation circuit, for counting an output signal of said oscillation circuit, said counter being reset when the level of the input signal of said apparatus is the same as the level of the output signal of said apparatus;

an output signal generating circuit, connected to said counter, for inverting the level of the output signal of said apparatus when a counter value of said counter reaches a predetermined value; and

wherein said oscillation circuit has a capacitor used to carry out said oscillation operation and said oscillation operation is not subject to a duty ratio of a chattering phenomenon.

2. The apparatus as set forth in claim 1 , wherein said coincidence circuit comprises:

an exclusive OR circuit for receiving the input signal of said apparatus and the output signal of said apparatus; and

an inverter, connected to said exclusive OR circuit, for inverting the output signal of said exclusive OR circuit.

3. The apparatus as set forth in claim 1 , wherein said oscillation circuit comprises:

a capacitor;

a charging and discharging circuit, connected between said coincidence circuit and said capacitor, for charging and discharging said capacitor when the level of the input signal of said apparatus is not the same as the level of the output signal of said apparatus;

a comparator, connected to said capacitor, for comparing a voltage level of said capacitor with a variable reference voltage; and

a reference voltage generating circuit, connected to said comparator, for generating said variable reference voltage in accordance with an output signal of said comparator,

said charging and discharging circuit charging and discharging said capacitor in accordance with the output signal of said comparator.

4. The apparatus as set forth in claim 3 , wherein, when the output signal of said comparator is a first level, said charging and discharging circuit charges said capacitor and said variable reference voltage is a first reference voltage; and

wherein, when the output signal of said comparator is a second level, said charging and discharging circuit discharges said capacitor and said variable reference voltage is a second reference voltage.

5. The apparatus as set forth in claim 3 , wherein said charging and discharging circuit comprises:

a charging circuit, connected to said coincidence circuit, said capacitor and said comparator, for charging said capacitor, when the level of the input signal of said apparatus is not the same as the level of the output signal of said apparatus and the output signal of said comparator is a first level;

a discharging circuit, connected to said capacitor and said comparator, for discharging said capacitor, when the level of the input signal of said apparatus is not the same as the level of the output signal of said apparatus and the output signal of said comparator is a second level; and

a rapid discharging circuit, connected to said coincidence circuit and said capacitor, for rapidly discharging said capacitor, when the level of the input signal of said apparatus is the same as the level of the output signal of said apparatus.

6. The apparatus as set forth in claim 5 , wherein said charging circuit comprises a first resistor and first and second transistors connected in series between a first power supply terminal and said capacitor, said first transistor being turned ON when the level of the input signal of said apparatus is not the same as the level of the output signal of said apparatus, said second transistor being turned ON when the output signal of said comparator is said first level,

said discharging circuit comprising a second resistor and a third transistor connected in series between said capacitor and a second power supply terminal, said third transistor being turned ON when the output signal of said comparator is said second level,

said rapid discharging circuit comprising a fourth transistor connected between said capacitor and said second power supply terminal, said fourth transistor being turned ON when the output signal of said coincidence circuit is at a level.

7. The apparatus as set forth in claim 6 , wherein each of said first and second transistors comprises a P-channel MOS transistor,

each of said third and fourth transistors comprising an N-channel MOS transistor.

8. The apparatus as set forth in claim 6 , wherein said reference voltage generating circuit comprises:

third, fourth and fifth resistors connected in series between first and second power supply terminals; and

fifth and sixth transistors, connected in series between terminals of said fourth resistor, for generating said variable reference voltage at a connection node of said fifth and sixth transistors,

said fifth transistor being turned ON when the output signal of said comparator is a first level,

said sixth transistor being turned ON when the output signal of said comparator is a second level.

9. The apparatus set forth in claim 8 , wherein said fifth transistor comprises a P-channel MOS transistor and said sixth transistor comprises an N-channel MOS transistor.

10. The apparatus as set forth in claim 1 , wherein said output signal generating circuit comprises a D-type flip-flop which fetches an inverted output signal of said D-type flip-flop in synchronization with an output signal of said counter.

11. A chattering eliminating apparatus comprising:

a coincidence circuit for receiving an input signal of said apparatus and an output signal of said apparatus to determine whether or not a level of the input signal of said apparatus is the same as a level of the output signal of said apparatus;

a capacitor;

a first resistor and first and second transistors connected in series between a first power terminal and said capacitor;

a second resistor and a third transistor connected in series between said capacitor and a second power supply terminal;

a fourth transistor connected between said capacitor and said second power supply terminal;

a comparator having a hysteresis characteristic, connected to said capacitor, for comparing a voltage level of said capacitor with a variable reference voltage;

a counter, connected to said comparator, for counting an output signal of said comparator; and

a flip-flop, connected to said counter, for inverting the output signal of said apparatus when a counter value of said counter reaches a predetermined value,

said first transistor being turned ON when the level of the input signal of said apparatus is not the same as the level of the output signal of said apparatus, said second transistor being turned ON when the output signal of said comparator is a first level,

said third transistor being turned ON when the output signal of said comparator is a second level,

said fourth transistor being turned ON when the level of the input signal of said apparatus is the same as the level of the output signal of said apparatus.