| 摘要 |
PURPOSE:To obtain steep and great attenuation, by adding crystal resonators so that the phase difference beween the input and output of LC constitution filter is an odd number times 90 deg. at the frequency desired for block of signal passage. CONSTITUTION:The equivalent circuit of the LC constitution filter consisting of coils L11,L12,L13,1m and capacitors C11,C12,C13,C14,C15,C1n added with crystal resonators X11 and X12 in parallel with the input and output terminals, is a mere series resonant circuit LO,CO as shown in Fig. a. The LC filter is no loss to the passing band and only the phase theta is shifted. Accordingly, when the phase difference the filter is an odd numbur times 90 deg., gyrator conversion is possible, Fig. a can equivalently converted to Fig.b, and it acts like the fourth order filter. Thus, by adding crystal resonators to a LC filter, steep and great attenuation can be obtained. |
