MPC8378E datasheet(80/128 Pages) FREESCALE

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MPC8378E PowerQUICC II Pro Processor Hardware Specifications, Rev. 8

Freescale Semiconductor

•

Differential Input Voltage, VID (or Differential Input Swing):

The differential input voltage (or swing) of the receiver, VID, is defined as the difference of the two

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

negative.

•

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.

•

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|.

•

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 63 as an example for differential waveform.

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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 =(VSDn_TX +VSDn_TX) ÷ 2=(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 54. Differential Voltage Definitions for Transmitter or Receiver

Differential Swing, VID or VOD = A – B

A Volts

B Volts

n_TX or

n_RX

n_TX or

n_RX

Differential Peak Voltage, VDIFFp = |A – B|

Differential Peak-Peak Voltage, VDIFFpp = 2

× VDIFFp (not shown)

Vcm = (A + B)/2

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