Jitter and Eye Measurements: Ideal Recovery Clock

All Transition Minimized Differential Signaling (TMDS) Clock and Data
signal jitter specifications are specified relative to an Ideal Recovery
Clock defined below. The Data jitter is not specified numerically, but
instead, an High-Definition Multimedia Interface (HDMI) device or cable
shall adhere to the appropriate eye diagram(s) when the Transition
Minimized Differential Signaling (TMDS) data signals are measured using an
Ideal Recovery Clock as a trigger source.

The Transition Minimized Differential Signaling (TMDS) Clock signal may
contain low-frequency jitter components, which can be tracked by a Sink's
clock recovery circuitry, and high-frequency components, which are not
typically tracked. The purpose of the Ideal Recovery Clock is to give an
accurate representation of link performance when used as a trigger for eye
diagram and clock jitter specifications. The eye mask specifies the
relationship of clock jitter to data jitter only indirectly.

For the purposes of jitter and eye diagram specification, the Ideal
Recovery Clock is defined relative to the Transition Minimized Differential
Signaling (TMDS) clock signal. The Ideal Recovery Clock shall be equivalent
to the signal that would be derived by a perfect PLL (Ideal Clock Recovery
Unit) with a jitter transfer function shown in 'Jitter Transfer Function'
Equation, when the Transition Minimized Differential Signaling (TMDS) clock
signal were input into that PLL. This jitter transfer function has the
behavior of a low pass filter with 20dB/decade roll-off and with a –3dB
point of 4MHz.
(See attached file: Jitter Transfer Function of ideal CRU.jpg)
For the purposes of compliance testing, a Clock Recovery Unit is used to
generate a Recovered Clock, which is meant to approximate the Ideal
Recovery Clock. This Recovered Clock is used for measurement of the jitter
and eye diagram.