The output skew is defined as the time difference between the delay on output channels while driving equal loads. It is important in the RGMII interface for the high-speed clock to synchronize the data on RX and TX lines with maximum allowed skew of 500 ps and maximum rise and fall transition times of 750 ps. Table 3-5 shows how TXV passes and how competitor can fail, for the lower skew and faster transition requirement.

• Figure 3-1 measures the rise-to-rise output channel-to-channel skew for A-to-B direction rising-edge input under standard RGMII loading condition of 5 pF for TXV (measuring 21 ps, tighter skew) vs competitor (measuring approximately 6x looser skew).
• Figure 3-2 measures fall or rise times for TXV (measuring 484 / 417 ps) vs competitor (measuring approximately 2x slower rise or fall times >750 ps), violating RGMII requirement.

Figure 3-1 TXV Outputs (5 pF 1.8 V to 3.3 V Up Translation at 125 MHz, 25°C)

Figure 3-2 Competitor Outputs (5 pF 1.8 V to 3.3 V Up Translation at 125 MHz, 25°C)

• As temperature increases to 125°C, Figure 3-3 compares TXV0108 (measuring 555 / 507 ps rise or fall times, 43 ps tighter rise-to-rise skew) with competitor (measuring approximately 4x looser skew and approximately 2x slower rise or fall times >750 ps), violating RGMII’s timing budget shown in Figure 3-4.

Figure 3-3 TXV Waveform (5 pF 1.8 V to 3.3 V Up Translation at 125 MHz, 125°C)

Figure 3-4 Competitor Waveform (5 pF 1.8 V to 3.3 V Up Translation at 125 MHz, 125°C)