kelly
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Hi VP1953,
It's basically noise. There is a noise requirement for the stage (it's a VGA) after the filter. The VGA input is biased to a voltage through pull up resistors, and they are in the Kohms range for minimum noise. So as far as the filter is concern, the Rl is pretty high. Not to mention the corner of the LC filter needs to be around 500MHz, so the inductor is huge. Since I am not too familiar with the LC filter, I am not sure whether you can build the LC for a infinite RL condition.
I guess you are saying the LC filter needs to be designed with a specific RL then? If that's the case, I can look at what's the maximum R VGA can use (trade that off with the noise) and design the filter based on that R then.
Thanks.
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