| Summary: | 碩士 === 國立清華大學 === 電子工程研究所 === 97 === In this thesis a switched-capacitor band-pass filter was designed for the application of electrocardiogram (ECG). The ECG signal had been acquired from the body. First of all, the signal was gained by using instrument amplifier. Then, noise and unwanted signal was filtered out by using band-pass filter, which was consisted of high-pass filter series with low-pass filters. High-pass filter, which cutoff frequency was at 0.05Hz and filtered out the dc bias and dc offset to avoid circuit working in saturation region. Then, two stages of low-pass filters filtered out noise at high frequency effectively, which cutoff frequency were at 100Hz and had a gain of nine for observing easily.
Due to the ultra low frequency specific, large resistances and capacitances were needed. Therefore the technique of switched-capacitor equivalent to resistance was designed. This design of switched-capacitor made the system only need a few pF of the capacitance could achieve the specification in place of large resistances, not only saved the areas, but also transferred the function to a ratio of capacitances, and it also made less error of production.
Due to the large capacitances were designed, the technique of capacitance multiplier was adopted too, capacitance multiplier was consisted of series many stages of current multiplier cells (CMC). CMC was composed of operational amplifiers which input pairs were virtual ground and inverters which used the same size for the same impendence, the current would be multiplied and the capacitance would also be multiplied. In the thesis ten thousands of capacitances was designed.
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