Digital noise filter
A digital noise filter circuit includes a gating clock generating circuit and a noise filter circuit. The gating clock generating circuit compares logic levels of an input signal and an output signal of the noise filter circuit. The gating clock generating circuit supplies a gating clock as an operating clock to the noise filter circuit when the logic levels of both signals do not coincide, and halts supply of the gating clock when the logic levels of both signals do coincide. The noise filter circuit removes noise from the input signal and outputting the resultant signal as the output signal.
1. A digital noise filter circuit comprising:
a gating clock generating circuit that compares logic levels of an input signal and an output signal, supplies a gating clock when the logic levels of both signals do not coincide and halts supply of the gating clock when the logic levels of both signals do coincide; and
a noise filter circuit, which is supplied with the gating clock as an operating clock, that removes noise from the input signal and outputs the resultant signal as the output signal.
2. The circuit according to claim 1 , further comprising a synchronizing circuit that receives the input signal in synch with a clock;
wherein said gating clock generating circuit compares the logic level of the input signal synchronized by said synchronizing circuit and the logic level of the output signal, and the gating clock is a clock synchronized to the clock of the synchronizing circuit.
3. The circuit according to claim 2 , wherein said noise filter circuit includes:
a shift register that shifts the synchronized input signal in synch with the gating clock;
a coincidence detecting circuit that detects coincidence among all stages of said shift register; and
a flip-flop that outputs any signal from among the stages of said shift register as the output signal in synch with the gating clock when said coincidence detecting circuit detects coincidence.
4. The circuit according to claim 3 , wherein the clock of said synchronizing circuit is supplied as the shift clock to a first stage of said all stages of the shift register.
5. The circuit according to claim 3 , wherein said all stages which said coincidence detecting circuit subjects to detection include the input signal to a first stage of said shift register and an output signal of a final stage of said shift resister, and said coincidence detecting circuit detects coincidence when the signals of each of the stages of the shift register all coincide.
6. The circuit according to claim 2 , wherein said noise filter circuit includes:
a counter circuit that counts the gating clock;
an edge detecting circuit that detects an edge of the synchronized input signal and resetting said counter circuit; and
a flip-flop that outputs the synchronized input signal as the output signal when said counter circuit reaches a prescribed counter value.
7. The circuit according to claim 6 , wherein said noise filter circuit further includes a comparator that compares a counter value from said counter circuit and a prescribed counter value that has been set in advance; and
said flip-flop outputs the synchronized input signal as the output signal in synch with the gating clock when said comparator detects that the prescribed counter value has been reached.
8. The circuit according to claim 6 , wherein said edge detecting circuit includes:
an edge-detecting flip-flop that receives the synchronized input signal in synch with the clock of said synchronizing circuit; and
an exclusive-OR gate to which the synchronized input signal and an output signal of said edge-detecting flip-flop are input;
an output signal from said exclusive-OR gate being connected to a reset terminal of said counter circuit.