Abstract:

Metal-oxide thin-film transistor (MO-TFT) can be utilized to create a flexible wearable system for detec-ting heart rate signals. However, the lack of high-performance complementary devices in MO-TFTs results in low gain for the implemented preamplifiers. Additionally, the relatively poor performance of MO-TFT devices poses challenges for the design of subsequent modules. In order to improve the gain of the preamplifier and reduce the performance requirements of the subsequent digital circuit, this paper proposed a common source common gate capacitor bootstrap structure preamplifier. The preamplifier was mainly composed of an external coupling bias module and a core amplifier module. The core amplifier module uses a capacitor bootstrapping technique known for its excellent stability, large output voltage swing, and low power consumption. This technique is combined with a cascode structure to enhance the overall gain of the circuit. The external coupling bias module utilizes an AC-coupled external bias structure that features low power consumption, high input impedance, and straightforward operating point setting, thereby meeting the bandpass requirements of the preamplifier for heart rate signal detection. The proposed preamplifier was designed and fabricated using a 10 μm IZO-TFT process. The test results indicate that with a 20 V power supply voltage, the circuit has a gain of 35 dB, a bandwidth of 2 Hz~2 kHz, a noise of 118.2 μV, and a power consumption of 0.1 mW. The presented preamplifier meets the requirements for detecting heart rate signals. In comparison to the current MO-TFT heart rate signal detection preamplifier, the gain has been increased by about 10 dB, which reduces the performance requirements of the subsequent digital module on the device, and is beneficial to achieve the digitalization of analog signals and maintain the signal integrity.

Key words: metal oxide thin film transistor, heart rate signal detection, preamplifier, capacitor bootstrapping