In this thesis some pH bio-transducers and their readout circuits were studied. The main target was to achieve a smart transduction. A PVTA (Process, Voltage, Temperature and Aging) variations compensation was included. The pH bio-transducers studied were the MIM-ISFET (Metal Insulator Metal - Ion Sensitive Field Effect Transistor), the integrated/discrete ISFGMOSFET (Ion Sensitive Floating Gage Metal Oxide Semiconductor Field Effect Transistor) and the ISFET (Ion Sensitive Field Effect Transistor) from the IMB-CNM (Instituto de Microelectrónica de Barcelona - Centro Nacional de Microelectrónica) as an ion sensitive transistor/capacitor. The transfer functions (Vth vs. pH, gm vs. pH, ID vs. pH, VG vs. pH y COX vs. pH) for every transducer were obtained and each transducer's sensitivity was determined.