Rev AN-2153 REV B
©2016 Finisar Corporation AN-2153 REV B
Page 5 of 6
20-May-2016
Appendix
The IEEE802.3bm D3p3 Annex 83E defines the chip to module CAUI-4 electrical interface.
The CAUI-4 chip to module channel insertion loss is specified to be up to 10 dB at the fundamental
frequency of 12.89 GHz.
This allocates 7.3 dB loss for the host, 1.5 dB insertion loss for the module, and up to 1.2 dB electrical
connector insertion loss.
The CTLE function defined in section 83E.3.1.6.1 corrects for the unwanted channel loss, present in the
host system. This distortion increases with frequency and length of the high speed interface.
The equalizer gain function is given by the following function :
𝐻(𝑓) =
𝐺𝑃1𝑃2
𝑍1
×
𝑗2𝜋𝑓+𝑍1
(𝑗2𝜋𝑓+𝑃1)(𝑗2𝜋𝑓+𝑃2)
Where
𝐻(𝑓)
is the CTLE transfer function
G
is the CTLE gain
𝑃1, 𝑃2
are the CTLE poles in Grad/s
𝑍1
is the CTLE zero in Grad/s
𝑗
is the square root of -1
𝑓
is the frequency in GHz
The graph below represents this function. CTLE gain refers to the relative amount of gain peaking at
12.89 GHz compared to low frequency required to compensate the channel loss over frequency. For
example a system that has a short trace length will require a smaller gain setting to correct for the channel
imperfections eg 1 dB, whereas a host board that implements a longer trace length between host ASIC to
module might require up to 9 dB of amplitude.
Finisar QSFP28 transceivers are characterized for CTLE, from IEEE802.3bm D3p3 Figure 83E-9.
