High-Speed Serial Interfaces (HSSI)
Using this waveform, the definitions are as follows. To simplify illustration, the following definitions
assume that the SerDes transmitter and receiver operate in a fully symmetrical differential signaling
environment.
•
•
•
Single-Ended Swing
The transmitter output signals and the receiver input signals SDn_TX, SDn_TX, SDn_RX and
SDn_RX each have a peak-to-peak swing of A – B volts. This is also referred as each signal wire’s
single-ended swing.
Differential Output Voltage, V (or Differential Output Swing):
OD
The differential output voltage (or swing) of the transmitter, V , is defined as the difference of
the two complimentary output voltages: V
or negative.
OD
– V . The V value can be either positive
SDn_TX
SDn_TX OD
Differential Input Voltage, V (or Differential Input Swing):
ID
The differential input voltage (or swing) of the receiver, V , is defined as the difference of the two
ID
complimentary input voltages: V
negative.
– V The V value can be either positive or
SDn_RX
SDn_RX. ID
•
•
Differential Peak Voltage, V
DIFFp
The peak value of the differential transmitter output signal or the differential receiver input signal
is defined as differential peak voltage, V = |A – B| volts.
DIFFp
Differential Peak-to-Peak, V
DIFFp-p
Since the differential output signal of the transmitter and the differential input signal of the receiver
each range from A – B to –(A – B) volts, the peak-to-peak value of the differential transmitter
output signal or the differential receiver input signal is defined as differential peak-to-peak voltage,
V
= 2 × V
= 2 × |(A – B)| volts, which is twice of differential swing in amplitude, or
DIFFp-p
DIFFp
twice of the differential peak. For example, the output differential peak-peak voltage can also be
calculated as V = 2 × |V |.
TX-DIFFp-p
OD
•
•
Differential Waveform
The differential waveform is constructed by subtracting the inverting signal (SDn_TX, for
example) from the non-inverting signal (SDn_TX, for example) within a differential pair. There is
only one signal trace curve in a differential waveform. The voltage represented in the differential
waveform is not referenced to ground. Refer to Figure 60 as an example for differential waveform.
Common Mode Voltage, V
cm
The common mode voltage is equal to one half of the sum of the voltages between each conductor
of a balanced interchange circuit and ground. In this example, for SerDes output,
V
= (V
+ V
) ÷ 2 = (A + B) ÷ 2, which is the arithmetic mean of the two
cm_out
SDn_TX
SDn_TX
complimentary output voltages within a differential pair. In a system, the common mode voltage
may often differ from one component’s output to the other’s input. Sometimes it may be even
different between the receiver input and driver output circuits within the same component. It is also
referred as the DC offset in some occasion.
™
MPC8377E PowerQUICC II Pro Processor Hardware Specifications, Rev. 2
Freescale Semiconductor
77
FREESCALE [ Freescale ]
