I have a question about ADRF6510 NF specification from a customer.
ADRF6510 NF characteristics is indicated in figure-28 and figure-29 in the datasheet.The lowest NF is 21dB at 50dB of gain and worst NF is 55dB at 2dB of gain. (BW:30MHz)The NF does not fall linearly while in the range of the gain over 35dB.
On the other views, the output noise density(figure-30,31) is not flat despite ADRF6510 used X-AMP architecture. I have heard that the X-AMP has flat output noise density characteristics. But the output noise density is rise with in the gain range of 25dB or more in figure-30, 31. (@BW=30MHz)
I guess the output noise density of programable filter is large, and I think that this cause the large NF.
Q1. The NF of ADRF6510 is larger compared with another VGA at same gain (ex. AD8366). Could you teach me why the minimum NF of ADRF6510 is larger than other VGA ?
Q2. The NF is more large when selected narrow band width of programable filter.
Could you teach me why the NF of narrow band width is larger than wide bandwidth is selected.
Q3. The output noise density, when narrower band is selected, is larger than wide bandwidth selected.(over the gain range of 25dB ~ 50dB)
Could you teach me why the output noise density change by band width ?
I modified my question at 15:11 07/09. ysuzuki