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Switched Capacitor Channel Select Filter (Read 1788 times)
aaron_do
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Posts: 1398
Switched Capacitor Channel Select Filter
Mar 30
th
, 2009, 1:27am
Hi all,
just wondering, is there any major reason why we wouldn't use a switched capacitor filter for a channel-select filter for a direct-conversion receiver? Suppose the filter needs to work with a signal as low as -80 dBm.
thanks,
Aaron
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there is no energy in matter other than that received from the environment - Nikola Tesla
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rf-design
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Reiner Franke
Posts: 165
Germany
Re: Switched Capacitor Channel Select Filter
Reply #1 -
Mar 30
th
, 2009, 1:56am
The reason is that there are alternatives with better efficiency.
For inband noise/power dominated designs the cap size is equal in continuous-time and switch cap filters.
But the sampling frequency should be a factor higher than the maximum rejection frequency. Otherwise rejection is limited by alias. Second to have an accurate frequency response the caps should charged within a fraction of the sampling period. The need much more current again. If you compare the required bias current of continuous versus discrete filter opamps there is a big factor.
That rules out switch cap!
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aaron_do
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Re: Switched Capacitor Channel Select Filter
Reply #2 -
Mar 30
th
, 2009, 7:45am
Thank you very much.
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there is no energy in matter other than that received from the environment - Nikola Tesla
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