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US 7,733,995 B2Granted
Noise filter and filtering method
AssigneeFujitsu Semiconductor Limited
InventorMinoru Usui
Life of this patent
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Abstract
A noise filter, used for a digital signal, configuring an [N−1]-stage filter by connecting the N-number of flip flops in series comprises a selection unit for outputting a filter output signal by selecting one of signals filtered by one to (N−1) stages based on a selection signals; and a wave form check unit for making the selection unit change a selection thereby by changing a value of the selection signal based on a pulse width on the filter output signal which is output from the selection unit.
Claims5
An {N−1}-stage noise filter, used for a digital signal, comprising:
- an N number of flip flops connected in series;
- at least an {N−1} number of AND circuits configured such that outputs from a first and a second of the flip flops are input to a first of the AND circuits, and for each n of 2≦n≦N−1, an output from an {n+1}-th of the flip flops and an output from an {n−1}-th of the AND circuits are input to an n-th of the AND circuits in order for each n-th AND circuit for 1≦n≦N−1 to be configured to output, as an output of an n-th stage filter in the noise filter, an AND of outputs of the first to {n+1}-th flip flops;
- a selection unit to output a filter output signal by selecting one of the outputs from the first to {N−1}-th AND circuits based on a selection signal;
- a wave form check unit to make the selection unit change a selection thereby by changing a value of the selection signal based on a pulse width on the filter output signal which is output from the selection unit;
- and
- a minimum pulse width designation register to set a minimum width of a pulse of said filter output signal, wherein
- said wave form check unit comprises,
- an output pulse width counter to count synchronously with an internal clock for a period of time when the filter output signal is high and to output a counted value;
- a comparison unit to compare an added value that is the counted value added by a filter value, which is determined by said selection signal, with a set value of said minimum pulse width designation register;
- and
- a filter output changeover counter to change the selection signal once the added value is less than the set value of the minimum pulse width designation register as a result of the comparison by the aforementioned comparison unit.
8 more elements
An {N−1}-stage noise filter, used for a digital signal, comprising:
- an N number of flip flops connected in series;
- at least an {N−1}number of AND means configured such that outputs from a first and a second of the flip flops are input to a first of the AND means, and for each n of 2≦n≦N−1 an output from an {n+1}-th of the flip flops and an output from an {n−1}-th of the AND means are input to an n-th of the AND means in order for each n-th AND means for 1≦n≦N−1 to be configured to output, as an output of an n-th stage filter means in the noise filter, an AND of outputs of the first to {n+1}-th flip flops;
- selection means for outputting a filter output signal by selecting one of the outputs from the first to {N−1}-th AND means based on a selection signal;
- wave form check means for making the selection means change a selection thereby by changing a value of the selection signal based on a pulse width on the filter output signal which is output from the selection means;
- and
- a minimum pulse width designation register for setting a minimum width of a pulse of said filter output signal, wherein
- said wave form check means comprises,
- an output pulse width counter for counting synchronously with an internal clock for a period of time when the filter output signal is high and outputting a counted value;
- a comparison means for comparing an added value that the counted value, added by a filter value, which is determined by said selection signal, with a set value of said minimum pulse width designation register;
- and
- a filter output changeover counter for changing the selection signal once the added value is less than the set value of the minimum pulse width designation register as a result of the comparison by the aforementioned comparison means.
8 more elements
A noise filtering method by an {N−1}-stage noise filter, used for a digital signal, comprising:
- inputting, to a first of at least an {N−1} number of AND circuits, outputs from a first and a second of an N number of flip flops connected in series;
- for each n of 2≦n≦N−1, inputting an output from an {n+1}-th of the flip flops and an output from an {n−1}-th of the AND circuits to an n-th of the AND circuits;
- outputting a filter output signal by selecting, based on a selection signal, one of the outputs from the first to {N−1}-th AND circuits where each output from each n-th AND circuit for 1≦n≦N−1 represents an AND of outputs of the first to {n+1}-th flip flops;
- and
- changing a value of the selection signal based on a pulse width on the filter output signal, wherein the changing includes,
- counting synchronously with an internal clock for a period of time when the filter output signal is high and outputting a counted value;
- comparing an added value that the counted value, added by a filter value, which is determined by said selection signal, with a set value of a minimum width of the pulse of said filter output signal;
- and
- changing the selection signal once the added value is less than the set value as a result of the comparison.
6 more elements
Dependencies are inferred from the claim text.