近幾年來不同生醫應用層面的植入式生理訊號量測系統發展趨向於微小化並搭配無線方式傳輸訊號。以整體系統來看，從電極端接收的生理訊號極為微弱，為了完整地記錄生理訊號，其電路設計上朝向低雜訊、高解析度、低功率消耗等特點邁進。 本篇主旨為提出一應用於生醫訊號量測系統之全差動對稱式類比前端電路，可針對極微弱的神經電圖(Electromyography, ENG)訊號作一記錄。為了將其中低頻的非理想成份諸如閃爍雜訊、直流偏移電壓等消除，提高其訊號雜訊比，以增加記錄的神經訊號的可辨度，本電路中放大級採用截波穩定型的技術。再者，為了降低整體電路的功率消耗，將輸入級的場效電晶體操作於弱反轉區。而截波穩定型放大器當中的帶通濾波器使用不同於一般濾波器的實現方式完成。本文提出架構由差動差分放大器與米勒積分器所構成，此架構可將從電極與電解溶液介面而產生的直流偏移電壓消除。 本文所提整體類比前端電路包含偏壓電路、時脈產生器、截波穩定型放大器、後置放大器、和二階連續時間低通濾波器。在電路實現上，在有效頻寬約9.3 KHz下，其直流電壓增益達到62.9 dB、總等效輸入相關雜訊電壓約為7.05 μVrms、其有效位元數達到10位元的解析度。使用台積電0.18 μm 標準CMOS 1P6M製程完成，其晶片面積為0.88 x 0.43 mm2。在1.8 V電源供應下，總功率消耗約為230 μW。 In recent years, the implanted bio-signal measurement devices for various bio-medical applications tend to be minimized and with wireless transmission capabilities. Since physiological signals from electrodes are very tiny and are difficult to be recorded, design of the bio-signal analog-front-end circuits are always with the features of low-noise, high resolution, and low power consumption. This work presents a fully differential and analog-front-end circuit for bio-signal measurement system that can be used to record the very tiny electroneurography (ENG) signals. Chopper stabilization technique (CHS) is employed in the amplification stage to eliminate the non-ideal low-frequency effects, such as the flicker noise and the DC-offset voltage. It improves the signal-to-noise ratio (SNR) and offers a higher resolution for the recorded neuron signals. In order to decrease the power dissipation of the system, input stages of field-effect transistors are designed to be operating at the weak-inversion region. In addition, the band-pass filter of the chopper-stabilized amplifier consists of a differential difference amplifier and a Miller integrator, which are different to the traditional design with passive resistors and capacitors. The purpose of this BPF is aimed to cancel out the DC-offset voltage from the electrode-electrolyte interface. The whole AFE circuit includes a bias circuit, a clock generator, a chopper stabilization amplifier, a post-amplifier, and a second-order continues-time low-pass filter. Such AFE circuit is implemented in the TSMC 0.18-μm one-poly six-metals CMOS process and provides a mid-band gain of 62.9 dB, a signal bandwidth approximates up to 9.3 KHz, a total equivalent input-referred noise of about 7.05 μVrms, and a 10-bit resolution. Supplied at 1.8 V, the proposed AFE circuit consumes around 230 μW. The chip area is 0.88 × 0.43 mm2.
