Medical Electronics ICs

Home Glucose Monitoring Systems Using Amperometry

There are several methods of glucose measurement sensing: infrared spectroscopy, reflectance photometry, and amperometry. Home glucose monitoring systems use either reflectance photometry or amperometry. Both technologies use an enzyme (glucose oxidase or hexokinase) that catalyzes the glucose reaction within the electrochemical test strip.

Amperometry determines the concentration of a material in a sample by measuring electric current passing through a cell that contains the solution. It is a proven technique that is widely used but improving performance and reliability levels (signal-to-noise ratio and repeatability) can be challenging, particularly as home glucose monitoring systems typically run on a 3 V battery supply.

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In an amperometric solution, a sensor measures the current generated in a chemical reaction from electrochemical strips with glucose oxidase enzymes. In general, three electrodes are used: a reference electrode, a control electrode, and a working electrode. Signal currents are usually less than 3000 nA full scale, so the I-to-V converter requires low input bias current. A low-pass filter with a cutoff of 80 Hz to 100 Hz is desirable to remove extraneous noise. It can be a simple two- or four-pole Butterworth filter design. Low power operational amplifiers with bandwidths of 50 kHz to 500 kHz should be adequate.

The AD8603/AD8607 and the award-winning AD8613 family of operational amplifiers offer low offset, low noise, very low input bias current and low power consumption. Operating on 2.7 V with bandwidths of 400 kHz @ –3 dB, they are ideal for portable applications. The AD8541/AD8542 CMOS rail-to-rail amplifiers offers 1 MHz bandwidth at a low power consumption of 45 µA per amplifier—ideal for monitoring applications with high source impedance.

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