Design of an integrated photo detector circuit for laser doppler blood flow monitoring

A method to measure the blood perfusion of tissue is to apply photons to tissue and measure the frequency shift of the Doppler shifted photons.. To avoid the use of fibers, a chip was designed which contains photodetectors and electronic circuitry to amplify the signal. This IC serves as an interface between the tissue and the signal processor, which transforms the electrical data to medical information about the perfusion of tissue. To be able to measure at various tissue depths, the die contains photodiodes at various distances from the laser To make the photo current less susceptible to noise and disturbances, the current is amplified. The circuit features very low noise electronic circuitry. The electrical input noise current of the circuit is comparable to the noise current of a resistor of 400 kΩ. The die area is 4.5 by 5 millimeter. The total area for photodiodes is about 0.93µm². The electronics, which is largely analog, require almost the rest of the available area.