外文原文一、a question for study or discussion1．Research background and purpose1.1 conceptualizeElliptic filter (Elliptic filter), also known as the Call filter (Cauer filter), is in the passband and stopband ripple of a filter. Elliptic filter when compared to other types of filters, in order under the same conditions with minimal fluctuations in the passband and stopband. Same as its wave in passband and stopband, which distinguish it from the Butterworth filter with flat passband and stopband and flat passband and the stopband ripple or resistance with flat, cut than the snow filter passband ripple.A low-pass filter with a frequency response range of the ellipse：Four-order low-pass elliptic filter frequency response。
1.2 scientific researchIn the low-frequency (600Hz=500KHz) commonly used in band-pass filter, large LC filters, poor stability, stability of Crystal filters, but can only be made of narrow-band filter, bad shock and vibration resistance. Active filters are small, but stability and decay characteristics are often poor, and debugging easy. Ceramic filter is poor and low-frequency seismic performance of low temperature coefficient. And than snow filter Butterworth filter transfer function is a polynomial divided by a constant, for the whole network, all zeros in infinite, only infinite stopband attenuation is infinite, and the elliptic filter in both with zeros and poles on the limited frequency. Zero ripple in the passband, that it has a minimum across the passband and stopband ripple, This is distinguished from Butterworth filter with flat passband and stopband。
