Biosensor apparatus and method with sample type and volume detection

Abstract

A biosensor apparatus and method with sample type and cell volume detection. The apparatus includes a sine wave generator to apply an AC signal to a biosensor cell containing a sample, a current-to-voltage converter, a phase shifter, a square wave generator, a synchronous demodulator, and a low pass filter which yields a signal proportional to the effective capacitance across the biosensor cell, which is proportional to the volume of the sample. In addition, the current-to-voltage converter yields a signal indicative of the type of sample contained within the biosensor cell. The method includes applying a sine wave to the biosensor cell, shifting the phase of the resultant signal, generating a square wave synchronous with the sine wave, demodulating the resultant signal with the square wave, and filtering the demodulated signal to produce a signal proportional to the effective capacitance across the biosensor cell. The biosensor apparatus and method are capable of determining sample type and measuring glucose levels over a wide range of sample volumes.

1 . An apparatus for measuring the effective capacitance across a biosensor cell having a first conductor connection and a second conductor connection, the biosensor cell configured to receive a sample having a volume, said apparatus comprising: 
 a sine wave generator having an output for coupling to the first conductor connection of the biosensor cell, said sine wave generator producing an AC signal;    a current-to-voltage (I/V) converter having an input for coupling to the second conductor connection of the biosensor cell and further having an output;    a phase shifter having an input coupled to the output of said I/V converter and further having an output;    a square wave generator producing a square wave synchronous with said AC signal;    a synchronous demodulator having an output, a first input coupled to said phase shifter, and a second input coupled to said square wave generator; and    a low pass filter (LPF) having an input coupled to the output of said synchronous demodulator, said LPF producing a signal at an output proportional to an effective capacitance across the biosensor cell.    
   
   
       2 . The apparatus of  claim 1 , further comprising: 
 a DC voltage source coupled to the first conductor connection of the biosensor cell, said DC voltage source adding a DC component to said first conductor.    
   
   
       3 . The apparatus of  claim 2 , wherein said phase shifter shifts the phase of a signal out of said I/V converter and removes said DC component from said signal out of said I/V converter.  
   
   
       4 . The apparatus of  claim 1 , further comprising: 
 an analog-to-digital (A/D) converter having an analog input coupled to the output of said LPF and further having a digital output, said A/D converter converting said signal proportional to the effective capacitance across the biosensor cell from analog to digital.    
   
   
       5 . The apparatus of  claim 4 , further comprising: 
 a processor coupled to the digital output of said A/D converter to process said digital signal proportional to the effective capacitance across the biosensor cell to derive the effective capacitance across the biosensor cell.    
   
   
       6 . The apparatus of  claim 5 , said processor further deriving the volume of the sample based on the effective capacitance across the biosensor cell.  
   
   
       7 . The apparatus of  claim 1 , wherein said sine wave generator generates a synthesized sine wave.  
   
   
       8 . The apparatus of  claim 7 , wherein said synthesized sine wave is a stair type sine wave.  
   
   
       9 . A biosensor for measuring components within a sample, said biosensor comprising: 
 a biosensor cell having a first conductor connection and a second conductor connection, said biosensor cell configured to receive the sample;    a sine wave generator coupled to the first conductor connection of said biosensor cell, said sine wave generator producing an AC signal having a determined frequency;    a current-to-voltage (I/V) converter having an input coupled to the second conductor connection of said biosensor cell and further having an output;    a phase shifter having an input coupled to the output of said I/V converter and further having an output;    a square wave generator producing a square wave synchronous with said AC signal;    a synchronous demodulator having an output, a first input coupled to the output of said phase shifter, and a second input coupled to said square wave generator; and    a low pass filter (LPF) having an input coupled to the output of said synchronous demodulator, said LPF producing a signal at an output proportional to an effective capacitance across said biosensor cell.    
   
   
       10 . The biosensor of  claim 9 , further comprising: 
 an analog-to-digital (A/D) converter having an analog input coupled to the output of said LPF and further having a digital output, said A/D converter converting said signal proportional to the effective capacitance across the biosensor cell from analog to digital.    
   
   
       11 . The biosensor of  claim 10 , further comprising: 
 a processor coupled to the digital output of said A/D converter to process said digital signal proportional to the effective capacitance across the biosensor cell to derive the volume of the sample.    
   
   
       12 . The biosensor of  claim 9 , further comprising: 
 a DC voltage source coupled to the first conductor of said biosensor cell, said DC voltage source adding a DC component to the apparatus.    
   
   
       13 . The biosensor of  claim 12 , wherein said phase shifter shifts the phase of a signal out of said I/V converter and removes said DC component.  
   
   
       14 . The biosensor of  claim 12 , further comprising: 
 an analog-to-digital (A/D) converter having a digital output and an analog input, said analog input coupled to the output of the I/V converter through a first switch and coupled to the output of said LPF through a second switch, only one of said switches being closed at a time.    
   
   
       15 . The biosensor of  claim 14 , further comprising: 
 a filter coupled between the I/V converter and the A/D converter in a path containing said first switch to remove an AC component from said path.    
   
   
       16 . The biosensor of  claim 14 , further comprising: 
 a processor coupled to the digital output of said A/D converter to process said digital signal proportional to the effective capacitance across the biosensor cell when said second switch is closed and to process the output of said I/V converter to determine if the sample is of a specific type when said first switch is closed.    
   
   
       17 . The biosensor of  claim 14 , wherein the sample is blood and the component is glucose, and wherein said processor further calculates the glucose level for the sample of blood using the derived volume.  
   
   
       18 . The biosensor of  claim 17 , wherein said DC voltage source is configured to apply a first voltage of a first polarity to said biosensor cell during a first period and to apply a second DC voltage of a second polarity to said biosensor cell during a second period.  
   
   
       19 . The biosensor of  claim 18 , further comprising: 
 a processor coupled to the digital output of said A/D converter to process said digital signal proportional to the effective capacitance across the biosensor cell when said second switch is closed, to process the output of said I/V converter when said first switch is closed to determine a first current through said biosensor cell during said first period and a second current through said biosensor cell during said second period, and determine a glucose level for said sample of blood based on said effective capacitance, said first current, and said second current.    
   
   
       20 . A method for measuring the effective capacitance across a biosensor cell having a first conductor connection and a second conductor connection, the biosensor cell configured for use in a biosensor to receive a sample having a volume, said method comprising the steps of: 
 applying a sine wave having a determined frequency to the first conductor connection of the biosensor cell to produce an AC signal;    shifting the phase of said AC signal;    generating a square wave synchronous with said sine wave;    demodulating said AC signal with said square wave to produce a demodulated signal; and    filtering said demodulated signal to produce a signal proportional to the effective capacitance across the biosensor cell.    
   
   
       21 - 28 . (canceled)