A Digitally Assisted Tunable High Pass Filter Based on Flexible a-IGZO TFTs for Biomedical Applications

This paper presents a digitally assisted tunable high pass filter for biomedical applications, implemented using unipolar a-IGZO TFTs manufactured on a flexible substrate. The proposed system is based on a master-slave approach. It takes advantage of the signal attenuation experienced in a high pass filter when a reference sinusoidal signal with a frequency lower than the cut off frequency is applied. The signal attenuation is monitored and a feedback loop automatically controls the small-signal resistance in the master and slave filters to obtain a specific signal attenuation, which in turn sets the passband frequency of the high pass filter. The presented approach is not only useful for setting a sub Hz cut off frequency but it is shown to be effective in counteracting parameter and supply voltage variations. The method presented in the paper can be also applied to Silicon biomedical circuits.