The goal of ELEN 6350 course is for students to acquire the fundamental skills of IC design. Under supervision, students go through the entire process of IC development process: defining the application and specifications of the IC, system and transistor level simulations, layout, parasitic extraction and post-layout simulations, tape-out to the foundry, and lastly functional verifications on the fabricated IC. The chip fabrication was generously donated by MOSIS under their educational program.
In this project, we design a pulse oximetry based heart rate monitor, a system that detects the user’s heart rate through changes in light signals collected from the user’s fingertip. The system monitors heart rates based on the photophlethysmogram (PPG) technique, a non-invasive method to detect blood volumetric change with a light source on one side of the fingertip and a photodetector on the other side. Because the blood volume in the fingertip pulses synchronously heart rate, we can induce the user’s heart rate simply from acquiring information in the fingertip. Figure 1 shows the principle of using PPG for our application.
The IC that we design consists of two operational transconductance amplifiers (OTAs) used to amplify the light signals, and a comparator to produce digital outputs from square waves generated from the amplifier signals. This IC operates with 1.2V supply voltage and 20uA bias current for each of its modules. Other components such as filters and microcontroller are included off-chip, and together with the IC they are hosted on a PCB to complete the system.
Figure 1. Principle of PPG