Testing

DC Testing

The IC was received on a Dual In-line 28 pin package (DIP28). It was assembled on a fabricated PCB and tested. To determine agreement between simulation and measurements in silicon, as a first step, the process corner of the fabricated chip was determined by running I-V sweeps on diode connected PMOS and NMOS test structures on the chip. The results are displayed in FIG 1. The NMOS is in the slow corner and the PMOS is in the fast corner.

nmos IV pmos IV
FIG 1. NMOS and PMOS I-V curves.

AC testing

The AC response of the Heart rate filter chain was characterized by introducing a sine wave at the input of the filter chain and looking at the response at the output of each of the stages.This was plotted against simulation to test agreement. There appears to be a mismatch, (possibly on account of component variations), in the first stage which propogates through all four stages. The results are in FIG 2.

Output of Stage1 Output of Stage2 Output of Stage3 Output of Stage4
FIG 2. AC response at the output of the different stages. (Blue, simulated and red crosses, measured).

Tests with the PPG sensor

The chip was then tested with the signal from the PPG sensor. The output of the sensor, the output of the heart rate filter chain and the output of the comparator are plotted in FIG 3. The corresponding signals for the respiratory rate filter chain are plotted in FIG 4.

HR scope waveforms
FIG 3. Scope waveforms of PPG sensor output (Green), Heart rate filter chain Output (Blue), Output from comparator (Yellow).
RR scope waveforms
FIG 4. Scope waveforms of PPG sensor output (Green), respiratory rate filter chain Output (Blue), Output from comparator (Yellow).


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