Apparatus and method for adjusting filter frequency in relation to sampling frequency

Abstract

A self-tuning filter is disclosed. The self-tuning filter includes a digital clocking signal and an input coupled to the digital clocking signal, whereby the input reads a value incident on the input when the digital clocking signal changes to a predetermined state. A clock-tunable filter is, furthermore, coupled to the digital clocking signal so that the frequency of the clock-tunable filter is adjusted in relation to a sampling frequency at which the digital clocking signal operates. The self-tuning filter may be applied to an input of a data acquisition unit and applied to an input having a variable sampling frequency. A method of controlling the frequency of a clock-tunable filter is also disclosed.

What is claimed is:  
     
         1 . In a data acquisition unit, a self-tuning filter, comprising: 
 a digital clocking signal;    an input coupled to said digital clocking signal, whereby the input reads a value incident on the input when the digital clocking signal changes to a predetermined state; and    a clock-tunable filter coupled to said digital clocking signal, whereby the frequency of the clock-tunable filter is adjusted in relation to a sampling frequency at which the digital clocking signal operates.    
     
     
         2 . The self-tuning filter of  claim 1 , wherein the clock-tunable filter is a low-pass filter.  
     
     
         3 . The self-tuning filter of  claim 1 , further comprising a frequency multiplier coupled to said digital clocking signal and said clock tunable filter, whereby the frequency of the clock tunable filter is a multiple of the sampling frequency.  
     
     
         4 . The self-tuning filter of  claim 3 , wherein the frequency multiplier is a phase-lock loop.  
     
     
         5 . The self-tuning filter of  claim 1 , wherein the input is an input of the data acquisition device.  
     
     
         6 . The self-tuning filter of  claim 1 , wherein the sampling frequency at which the digital clocking signal operates is equal to the frequency at which the digital clocking signal changes to the predetermined state.  
     
     
         7 . The self-tuning filter of  claim 1 , wherein the value incident on the input is a signal originating at a sensor.  
     
     
         8 . The self-tuning filter of  claim 7 , wherein the sensor is a pressure sensor.  
     
     
         9 . The self-tuning filter of  claim 1 , wherein the sampling frequency varies.  
     
     
         10 . The self-tuning filter of  claim 9 , wherein the sampling frequency varies as a function of a degree of rotation of a shaft.  
     
     
         11 . In a data acquisition unit, a self-tuning filter, comprising: 
 a digital clocking signal;    an input coupled to said digital clocking signal, whereby the input reads a value incident on the input when the digital clocking signal changes to a predetermined state and the digital clocking signal changes to the predetermined state at a varying rate;    a phase-lock loop coupled to said digital clocking signal; and    a clock-tunable filter coupled to said phase-lock loop, whereby the frequency of the clock tunable filter is a multiple of the sampling frequency at which the digital clocking signal changes to the predetermined state.    
     
     
         12 . A method of controlling the frequency of a clock-tunable filter, comprising: 
 sensing a frequency at which a digital clocking signal changes state, whereby said digital clocking signal causes an input to read a value incident on the input when the digital clocking signal changes to a predetermined state;    adjusting a frequency of a clock-tunable filter in relationship to the frequency at which the digital clocking signal changes state.    
     
     
         13 . The method of  claim 12 , further comprising: 
 multiplying the frequency of the digital clocking signal to acquire a desired filter frequency; and    wherein said adjusting includes adjusting the frequency of the clock-tunable filter to equal the desired filter frequency.    
     
     
         14 . The method of  claim 12 , wherein the digital clocking signal changes state at a varying rate.