T1022 SerDes Recommended Input Voltage

[jack_mcculloch]

Hi,

We are looking to drive a SFP directly from a SerDes output on the T1022. But there is some confusion on what the recommended signals levels for this interface is.

The T1022 has a max V_RX-DIFFp-p of 1.6V in 1000Base-KX mode (table 44) my understanding is that will equate to an allowable 0.8V single ended voltage swing on a SerDes input?

The SFP MSA states that a SFP can output a signal that is 2V differential (1v singled ended). This exceeds the max of the T1022, but note 1 on table 44 refers to table 3 for recommended operating conditions. Table 3 states SerDes inputs have a recommend range of GND to S1V_DD this suggests that the SFP would be ok?

Would this also apply when operating in SGMII mode (table 39)?

Thanks,

Bob

[Bulat · Accepted solution]

Table 3 states that Serdes inputs are tolerant to GND to S1VDD signals level, so 1V is ok.
Table 44 directly states/repeats IEEE 802.3 specifications for 1000Base-KX receiver (clause 70.7.2).
Table 43 provides IEEE 802.3 specifications for 1000Base-KX transmitter (clause 70.7.1), here you can also see 1600mV maximum. If a SFP outputs V_TX-DIFFp-p 2V (2000mV instead of 1600mV), it does not comply with the standard. However there is no electrical problem from the T1022 side due to table 3 specs.
Same applies to SGMII mode.

Regards,

Bulat