High-Speed Serial Interfaces (HSSI)
Using this waveform, the definitions are as follows. To simplify the illustration, the following definitions
assume that the SerDes transmitter and receiver operate in a fully symmetrical differential signaling
environment.
1. Single-ended swing
The transmitter output signals and the receiver input signals SD_TX, SD_TX, SD_RX and SD_RX
each have a peak-to-peak swing of A – B volts. This is also referred as each signal wire’s
single-ended swing.
2. 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
OD
the two complimentary output voltages: V
or negative.
– V
. The V value can be either positive
SD_TX
SD_TX OD
3. 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
SD_RX
SD_RX ID
4. 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
5. 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-to-peak voltage can also be
calculated as V
= 2 × |V |.
TX-DIFFp-p
OD
6. 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
cm_out
SD_TX
+ V
= (A + B)/2, which is the arithmetic mean of the two complimentary output voltages
SD_TX
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 to as the DC offset.
MPC8548E PowerQUICC™ III Integrated Processor Hardware Specifications, Rev. 6
Freescale Semiconductor
61
FREESCALE [ Freescale ]
