Among the sensors that imitating the human five senses, the visual sensors are commercialized as CIS (CMOS Image Sensor) and CCD (Charge Coupled Device), and tactile sensor are partly commercialized as a touch sensor. Also, auditory sensor is commercialized as a microphone. However, the smell and taste sensors are still under development.

If the taste is sensed electrically, it is possible to obtain standard taste information. For portable applications a small size taste sensor system is required and a suitable technology for manufacturing such a highly sensitive small-sized sensor is semiconductor technology. Conventional taste sensors require a large amount of test material because they are large in volume. Also require expensive equipment and not suitable for portable device.

Various types of biosensors have been developed to overcome these drawbacks. The FET-type biosensor has advantages of miniaturization and standardization by integrating the sensor and the circuit by utilizing the integrated circuit manufacturing process. Among the devices capable of integrated circuits, thin film transistors with oxide semiconductor materials are one of the candidates having a simpler process than the LTPS TFT and a higher field effect mobility than the a-Si TFT.

Depending on the taste substances, the emitter current in the FET sensor changes. Each taste solution and lipid sensing membrane have different sensing principles. For example, a sourness, saltiness, or sweetness solution are electrochemical reactions in which specific ions are assembled near the lipid sensing membrane by electrical attraction, the bitterness solution is hydrophobic and certain molecules are absorbed by the lipid sensing membrane Hydrophobic binding. Those reactions induce potential changes of the floating gate and changes the current of the device.

As the concentration of the taste substances increases, the current of the transistor increases. And each solution has different values depending on the lipid sensing membrane. In this paper, an oxide transistor-based amplifier is designed for a taste sensor. We designed an amplifier that works well even when the size of the transistor changes and the threshold voltage changes.

Usually amplifier circuit require the optimum operation bias, which make the circuit complicated. However, in this paper we proposed a cascaded Class A amplifier which uses self-bias unit instead of voltage divider by resistors as shown in figure. In this circuit, T3 is a taste sensing transistor. Sensing signal is amplified by supply the alternation voltage through capacitor. The alternative way is to use T4 as a taste sensor. The amplification gains for different location of the sensor were compared.