A digitally assisted tunable high pass filter for biomedical applications, implemented with unipolar a-IGZO TFTs is discussed in this paper. The presented system leverages the signal attenuation by the high pass filter when a reference sinusoidal signal with a frequency lower than the cut off frequency is applied, to tune a master-slave filter structure. The results presented in this paper show that sub Hz cut off frequencies can be obtained with less than 5 % relative error in presence of large parameter and supply variations. The proposed tuning scheme can be applied to improve the precision of high pass filters for biomedical applications implemented in a-IGZO and also in Si, while keeping a hardware minimalistic and compact approach.