| dc.description.abstract | As modern medicine advances, the portable bio-medical measurement device has become the favorable trend currently. It is expected that the patient can carry light devices for long-term monitoring the physical conditions. In recent years, the bio-signal measurement devices for various bio-medical applications tend to get minimized in collaboration with wireless transmission capabilities.
The purpose of this thesis is to propose a low noise analog-front-end circuit for bio-signal measurement system comprised by a programable gain amplifier and a SC-SO delta-sigma modulator in order to record different bio-signals like Electronencephalogram (EEG) and Electrocardiography (ECG) signals. While the circuit operates at low frequencies, a tunable pseudo-resistor with a huge resistance is seriously required for an extremely low frequency pole to minimize the non-ideal effects, including DC-offset, flicker noise, on chip design, and the like. The issues of process variation and DC-offset from electrode the pseudo-resistor can therefore be resolved. On the other hand, the input stage MOS of the operation amplifier are designed to operate at the weak-inversion region in order to reduce the power consumption and thermal noise effect and obtain better performance than MOS in saturation. Overall, the AFE circuit aims at low power consumption, low-noise, and high resolution.
In this research, a bio-amplifier that employs a voltage-controlled-pseudo-resistor is designed based on weak-inversion technique to achieve tunable bandwidth and extensive operation voltage range for biomedical applications. Through ultra-high resistance for ac coupling, the versatile pseudo-resistor eliminates the dc offset from electrode-tissue interface. Since the voltage-controlled-pseudo-resistor consists of serial-connected PMOS transistors working at the subthreshold region and an auto-tuning circuit, it promises the constant (time-invariant) control-voltage of the pseudo-resistor. Such bandwidth-tunable bioamplifier is designed in a 0.18-um standard CMOS process, achieving gain at 40.2 dB with 10.35-uW power consumption. In addition, the proposed chip can also be used to develop the proof-of-concept prototype, with operation bandwidth at 9.5 kHz, input-referred noise at 5.2 uVrms from 6.3 Hz to 9.5 kHz, 5.54 uVrms from 250 Hz to 9.5 kHz, and tunable cutoff-frequency from 6.3 Hz to 600 Hz.
A bias circuit, a pseudo-resistor, an ac coupling band-pass filter, and common-mode feedback circuit are included in the VGA circuit. With the input signal at 1 kHz sine wave with 150 uW amplitude, the AFE achieves mid-band gain of 72 dB. In the meantime, when the input signal is 200 Hz sine wave with 2 mV amplitude, the AFE achieves mid-band gain of 58 dB. For the programmable low-cutoff frequency, it ranges from 4 to 300 Hz. Moreover, the input referred noise is 3.61 uVrms, and the THD is 60.2 dB. The circuit is fabricated in the TSMC 0.18-um one-poly six metals CMOS process, and the chip area is 0.68 mm^2. Finally, the simulated power consumption is around 55 uW for 1.8 V power supply.
In this thesis, a delta-sigma A/D converter consists of SDM and decimation filter. The proposed SDM is characterized with the advantages of Switched-Capacitor SDM (SC-SDM) and Switched-OPAMP SDM (SO-SDM). Aiming at low power consumption and high resolution, the SDM is accomplished for all applications of bio-signal measurement. It is found that, with an oversampling ratio (OSR) of 128, and 0.2 Vpp amplitude, the modulator achieves 86.47 dB signal-to-noise and distortion ratio (SNDR), 13.97 effective number of bits (ENOB) , and power consumption 318 uW at 10-kHz signal bandwidth. The measurement results show that signal to noise distortion ratio at 77.57 dB, 12.59 ENOB, and the measured power consumption around 392 uW for 1.8V power supply.
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