Hi all,

Please advice to me.

In the datasheet 33 page ~ "DIGITAL DOWNCONVERTERS (DDC)" @ AD9625,

I can not understand the calculation of the transition band.

"HIGH BANDWIDTH DECIMATOR

"The filter yields an effective bandwidth of 120 MHz, with a transition band of 156.5 MHz − 120 MHz = 36.5 MHz.

Therefore, the two-sided complex bandwidth of the filter is 240 MHz. "

1.What is the "156.5 MHz" ?

"LOW BANDWIDTH DECIMATOR

"The filter yields an effective bandwidth of 60 MHz, with a transition band of 81.25 MHz − 60 MHz = 21.25 MHz.

Thus, the two sided, complex bandwidth of the filter is 120 MHz. "

2.What is the "81.25MHz" ?

Best Regards,

sss

Hi Satoshi-

I can add a picture to Judy's description to visually describe the answer to your question:

1: 156.5MHz is equal to a half band of 2500MSPS/8. The filter is not perfectly flat across that band, so the effective portion is smaller than 156.5Mhz, or 120MHz in this case.

2. 81.25Mhz in this example is equal to a half band of 2500MSPS/16. The filter is not perfectly flat across that band, so the effective portion is smaller than 81.25Mhz, or 60MHz in this case.

Thanks,

Ian Beavers