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滤波器设计人员面临的最困难问题之一是得到严格容差、低损耗、匹配的电容。用一个通用的有源滤波器芯片(Burr-Brown公司的UAF42,它包含运放、增益调节电阻和片上精度0.5％的1000pF电容),就可以解决此困难问题。此外,该滤波器也没有与转换电容滤波器有关的异常现象和转换噪声。 片上的另一个高性能运放可以用于缓冲增益、实极电路或把高通和低通输出合起来产生一带阻滤波器(陷波滤波器)。本电路设计示出一个使用两片UAF42 IC和12个外接电阻的50Hz和100Hz陷波滤波器(见图)。这种电路是在人们需要采用精密滤波器来消除交流电源的低频交流声时应运而生的。
One of the most difficult problems that filter designers face is the ability to get tight tolerances, low losses, and matched capacitances. A common active filter chip (Burr-Brown’s UAF42, which contains op amps, gain adjustment resistors and a 0.5pF on-chip 1000pF capacitor) can solve this difficult problem. In addition, the filter also has no anomalies associated with switched capacitor filters and switching noise. Another on-chip high-performance op amp can be used to buffer gain, real-world circuitry or combine high-pass and low-pass outputs to create a band-stop filter (notch filter). This circuit design shows a 50Hz and 100Hz notch filter using two UAF42 ICs and 12 external resistors (see picture). This kind of circuit came into being when people need to use precision filter to eliminate AC hum of AC power.