Tool/software:
Could I disable the equalization of a TI PCIe redriver by setting the EQ index to 0?
Using the structure of the TI Gen 5 redrivers as an example, the CTLE/EQ circuits for each channel are organized as three amplifiers:
The signal path will always include the EQ Boost 1 and EQ Boost 2 amplifiers and they cannot be bypassed. Their individual settings will affect the overall filter shape and therefore the amount of boost applied to the signal, but even the minimum settings for EQ Boost 1 and EQ Boost 2 will not have a flat filter shape; they are still applying equalization (frequency-selective gain) to the signal.
The EQ index system organizes combinations of settings for the three amplifiers in a way that is much simpler to work with, numbered from 0 to 19 along with a unique "Default" setting. The lowest EQ index of EQ 0 has Boost 1 set to the minimum setting, Boost 2 set to the minimum setting, and Boost 1 (2nd order) bypassed:
EQ 0 is therefore the lowest possible EQ setting for the redriver, and in the example of the DS320PR810 it still provides about 4 dB of EQ boost at Gen 5 speeds. Therefore, it is not possible to disable the equalization of a TI PCIe redriver, it can only be reduced to a small value. This is important to consider during system evaluation and design. For example, a redriver EVM with the device EQ set to 0 does not function the same as a passive insertion loss card. As another example, an active mux or redriver mux such as the SN75LVPE5412 cannot operate equivalently to a passive mux by setting the EQ to 0, and therefore should not be cascaded with other redrivers.
A final clarification - the GUI shows a "Mute EQ" feature as seen in the above screenshot, however it turns off the output driver and leads to no signal being sent by the redriver, and does not cancel out the equalization while leaving the original signal intact.
Best,
Evan Su
