A safe circuit for the measurement of stimuli pulse amplitude in biomedical devices

In this paper an integrating amplifier aimed at estimating pulse amplitude in implantable stimuli delivery devices is presented. The proposed circuit can integrate during each stimulus the effective voltage being applied to tissue, to later use this measure in a self-calibration procedure or in a closed loop stimulator scheme. The circuit was designed and simulated using a 0.6 μm HV CMOS technology, it consumes only 8 μA current from the battery when it is turned on, and shows an error below 3% for pulses ranging from 100 μs to 5 ms, and from 350 mV to 15 V if the time-voltage product does not saturate the integrating capacitor. The circuit is safe in the sense it is not harmful for the patient in the case of a single (independent) circuit failure. The focus of this work is in a pacemaker application, but the developed circuit block can be incorporated in a wide set of biomedical devices.