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Hi
I've read application note how to create solid state voice recorder using flash msp430 http://www.ti.com/lit/an/slaa123/slaa123.pdf It says that simple RC filter at the output does the bandwidth limiting with a cutoff frequency approximately 2.7 KHz. On the contrary my calculation show that cutoff frequency is 1.578 KHz. Is there any mistake in schematic design?
Ilmars said:Did you take in account that resistors of Butterworth filter differ?
It is not a Butterworth filter, it is a simple series-R shunt-C low pass filter. The -3dB rolloff point is simply 1/RC.
Brian Boorman said:It is not a Butterworth filter, it is a simple series-R shunt-C low pass filter. The -3dB rolloff point is simply 1/RC.
Correct me if I am wrong, but I know following filter as Butterworth filter of Sallen-Key topology:
Ilmars
The answer was about microphone preamplifier and filter but you're talking about serial DAC and filter.
Vladimir Redzhepov said:The answer was about microphone preamplifier and filter but you're talking about serial DAC and filter.
You did not mention "microphone" nor "preamplifier" in your initial post. How would I know that you mean input filter by saying following words (pay special attention to word "output"):
Vladimir Redzhepov said:It says that simple RC filter at the output does the bandwidth limiting with a cutoff frequency approximately 2.7 KHz
Yes, then it seems like mistake. Good for you that you checked it :) Also it would be good idea to test frequency response of whole device during prototyping.
Ilmars said:You did not mention "microphone" nor "preamplifier" in your initial post.
Llmars - You are correct, and it confused me at first as well, until I asked Acrobat to search the PDF for the word "2.7 KHz" and the only hit was in the preamp/filter narrative.
There it is just an amplifier with an RC tacked on the output.
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