DS280DF810: DS280DF810 and DS110DF410

Hi David,

CTLE equalizes high frequency content.  This is typically sufficient to compensate for insertion loss since insertion loss typically primarily attenuates high frequency content. The VGA can help with recovering signals that have a low amplitude across the frequency spectrum.

Thanks,

Drew

Hi David,

The VGA provides a fixed boost regardless of frequency.  This is particularly helpful in cases where the TX link partner launch amplitude is low.  Since VGA is also a linear stage, it will not suppress any crosstalk or noise on the device's receiver.

Regarding the equalization provided by the VGA, I don't have an exact figure, but I think you can use the recommendations from the table below to get a rough perspective of how much equalization it can provide.

The VGA is a functional block that was not added to our retimers until the 25/28G generation (with the exception of the DS125DF1610).

Thanks,

Drew

Hi David,

I believe your understanding is incorrect.  My understanding is that the function of de-emphasis or pre-emphasis is to increase the amplitude of the high frequency content of a signal relative to the low frequency content.  This is so that after the signal passes through a typical transmission medium, the high frequency content amplitude is not as small relative to the low frequency content amplitude.

CTLE would be responsible for boosting high frequency content and thus might be more interchangeable with pre/de emphasis.

Also, VGA may be useful if significant de-emphasis is used.  This is because de-emphasis lowers the transmit amplitude of the low frequency content of the signal.  If the signal reaching the retimer receiver has low amplitude across the frequency spectrum, it might be useful to use the VGA to increase the amplitude.

Thanks,

Drew