GTP RXLPM_INCM_CFG and RXLPM_IPCM_CFG use for different VCM

[dick0329]

I use GTP RX and set RX_CM_SEL[1:0] = 2'b10 (float mode) in my design,

I don't know how to set GTP RXLPM_INCM_CFG and RXLPM_IPCM_CFG for different VCM,

My design need receive differential signal with VCM possible range from 0.3V to 0.9V (not dynamic change),

I have read below AR but not suitable for my application,

https://www.xilinx.com/support/answers/51448.html

What is the VCM ranges for RXLPM_INCM_CFG and RXLPM_IPCM_CFG?

Does only one of RXLPM_INCM_CFG and RXLPM_IPCM_CFG must set to 1'b1 (can not both set to 1'b1 or 1'b0)?

Thank You~

[venkata]

Which protocol are you trying to implement? Are you trying to do DC coupling with GTP?

Whether the termination mode "programmable" is suitable for you?

[dick0329]

This protocols are used for Panel Manufacturer to drive Source Driver IC (Such CHPI, CMPI, iSP, ...),

All of this protocols use DC Couple, but have different VCM (0.3V ~ 0.9V) and line rate (1.3Gbps ~ 3Gbps),

Those protocols need 100ohm termination resistor in RX side and have already described in standard spec,

I think "programmable mode" cannot be used, so I set RX_CM_SEL[1:0] = 2'b10 to use "float mode",

Unfortunately, RX_CM_TRIM[3:0] can not use in "float mode",

How GT know the current receiving VCM voltage, and choose suitable internal bias voltage in push-push mode configuration?

[venkata]

XAPP1096 provides an analysis for DC coupling use case with 7-series GTX. Check if it helps for your requirement.
https://www.xilinx.com/support/documentation/application_notes/xapp1096-dc-coupling-gtx-transceivers.pdf

[gguasti · Accepted solution]

hello,
The AC-coupling is recommended. If you must use the DC-coupling, please be careful with common mode currents. The receiver bias should match the signal common mode and the two ports
RXLPM_INCM_CFG
RXLPM_IPCM_CFG
are needed to enable the high/low common mode operation.

I do not find a characterization for common mode from 0.3V to <0.8V

At 0.3V I would try with
RXLPM_INCM_CFG = 0
RXLPM_IPCM_CFG = 1
RX_CM_TRIM [3:0] = 4’b0011 – 300 mV

RX_CM_SEL [1:0] = 2'b11

Because it is very close to Use mode 1 (table 4-3). Unfortunately I have no additional data. Please check with a PRBS checker the link quality. (https://www.xilinx.com/support/documentation/application_notes/xapp884_PRBS_GeneratorChecker.pdf)

From 0.8 to 0.9V (please see the UG) you can use the following configuration:
RXLPM_INCM_CFG = 1
RXLPM_IPCM_CFG = 0

RX_CM_TRIM [3:0] = 4’b1010 – 800 mV
RX_CM_TRIM [3:0] = 4’b1011 – 850 mV
RX_CM_TRIM [3:0] = 4’b1100 – 900 mV

RX_CM_SEL [1:0] = 2'b11

hope this helps

[dick0329]

@gguasti

It work well, Thanks~