PPC8567ECVTANJGA datasheet(62/139 Pages) FREESCALE

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MPC8568E/MPC8567E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 1

Freescale Semiconductor

High-Speed Serial Interfaces (HSSI)

The Differential Input Voltage (or Swing) of the receiver, VID, is defined as the difference of the

two complimentary input voltages: VSD_RX – VSD_RX. The VID value can be either positive or

negative.

4. Differential Peak Voltage, VDIFFp

The peak value of the differential transmitter output signal or the differential receiver input signal

is defined as Differential Peak Voltage, VDIFFp = |A – B| Volts.

5. Differential Peak-to-Peak, VDIFFp-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, VDIFFp-p = 2*VDIFFp = 2 * |(A – B)| Volts, which is twice of differential swing in

amplitude, or twice of the differential peak. For example, the output differential peak-peak voltage

can also be calculated as VTX-DIFFp-p = 2*|VOD|.

6. Common Mode Voltage, Vcm

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, Vcm_out = VSD_TX

+ VSD_TX = (A + B) / 2, which is the arithmetic mean of the two 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.

Figure 39. Differential Voltage Definitions for Transmitter or Receiver

To illustrate these definitions using real values, consider the case of a CML (Current Mode Logic)

transmitter that has a common mode voltage of 2.25 V and each of its outputs, TD and TD, has a swing

that goes between 2.5 V and 2.0 V. Using these values, the peak-to-peak voltage swing of each signal (TD

or TD) is 500 mV p-p, which is referred as the single-ended swing for each signal. In this example, since

the differential signaling environment is fully symmetrical, the transmitter output’s differential swing

(VOD) has the same amplitude as each signal’s single-ended swing. The differential output signal ranges

Differential Swing, VID or VOD = A – B

A Volts

B Volts

SD_TX or

SD_RX

SD_TX or

SD_RX

Differential Peak Voltage, VDIFFp = |A – B|

Differential Peak-Peak Voltage, VDIFFpp = 2*VDIFFp (not shown)

Vcm = (A + B) / 2

PPC8567ECVTANJGA Datasheet(PDF) 62 Page - Freescale Semiconductor, Inc