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Notch Filter is DC Accurate- 03/02/95 EDN Design Ideas: Most active filters exhibit noise, distortion, gain error, and dc offset. However, a filter topology that separates the dc and ac paths can eliminate the last two of these unwanted behaviors (Fig 1a). The dc path in this circuit has no op amps and, therefore, no dc offset. The dc path does not have a dc gain error other than -6 dB of attenuation that the R1/R2 divider causes. (This attenuation is absent if you omit the R2 termination. ) The ac path consists of C1 and a synthetic inductor comprising two wideband transconductance amplifiers and associated components. The result is an active circuit that emulates the passive filter of Fig 1b Design by Gary Sellani, Maxim Integrated Products, Sunnyvale, CA |
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