| dc.description.abstract | With the advances in modern medicine, portable bio-medical measurement device is the current trend. We hope that the patient can carry light device for a long time monitoring. In recent years, the bio-signal measurement devices for various bio-medical applications trend to be minimized and with wireless transmission capabilities.
This work presents a low noise analog-front-end circuit for bio-signal measurement system that can be used to record different bio-signal such as Electronencephalogram (EEG) and Electrocardiography (ECG) signals. When circuit operates at low frequencies, we need a tunable pseudo-resistor with a huge resistance to form a very low frequency pole to minimize the non-ideal effect such as DC-offset, flicker noise, and on chip design. Then, the pseudo-resistor can resolve process variation and DC-offset from electrode. In addition, in order to reduce the power consumption and thermal noise effect, the input stage MOS of the operation amplifier are designed to operate at the weak-inversion region and to get better performance than MOS operate in saturation. The AFE circuit is aiming at low power consumption, low-noise, and high resolution.
The whole AFE circuit includes a bias circuit, pseudo-resistor, ac coupling band-pass filter, and common-mode feedback circuit. When the input signal is 1 kHz sine wave with 150 μV amplitude, the AFE achieves mid-band gain of 72 dB, and when the input signal is 200 Hz sine wave with 2 mV amplitude, the AFE achieves mid-band gain of 58 dB. The programmable low-cutoff frequency ranges from 4 to 300 Hz; the input referred noise is 3.61 μVrms; and the THD is 60.2 dB. The circuit is fabricated in the TSMC 0.18-μm one-poly six metals CMOS process, and the chip area is 0.68 mm2. The simulated power consumption is about 55 μW for 1.8 V power supply. | en_US |