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March 31, 2008

IDT80KSW0004

Datasheet

Signal Definitions

LP-Serial links uses differential signaling. This section defines terms used in the description and specification of differential signals. Differential Peak-

Peak Voltage of Transmitter or Receiver shows how the signals are defined. The figure shows waveforms for either a transmitter output (TD and TD)

or a receiver input (RD and RD). Each signal swings between A Volts and B Volts where A > B. Using these waveforms, the definitions are as follows:

1.

The transmitter output signals and the receiver input signals TD, TD, RD and RD each have a peak-to-peak swing of A - B Volts

2.

The differential output signal of the transmitter, VOD, is defined as VTD-VTD.

3.

The differential input signal of the receiver, VID, is defined as VRD-VRD.

4.

The differential output signal of the transmitter and the differential input signal of the receiver each range from A - B to -(A - B) Volts.

5.

The peak value of the differential transmitter output signal and the differential receiver input signal is A - B Volts

6.

The peak-to-peak value of the differential transmitter output signal and the differential receiver input signal is 2 * (A - B) Volts

Figure 14 Differential Peak-Peak Voltage of 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 2.5V and 2.0V. Using these values, the peak-to-peak voltage swing of the

signals TD and TD is 500 mV p-p. The differential output signal ranges between 500 mV and -500 mV. The peak differential voltage is 500 mV. The

peak-to-peak differential voltage is 1000 mV p-p.

Equalization

With the use of high speed serial links, the interconnect media will cause degradation of the signal at the receiver. Effects such as Inter-Symbol

Interference (ISI) or data dependent jitter are produced. This loss can be large enough to degrade the eye opening at the receiver beyond what is

allowed in the specification. To negate a portion of these effects, equalization can be used. The equalization technique implemented in the CPS-12 is

Pre-emphasis on the transmitter (under register control).

Explanatory Note on Transmitter and Receiver Specifications

AC electrical specifications are given for transmitter and receiver. Long run and short run interfaces at three baud rates (a total of six cases) are

described.

The parameters for the AC electrical specifications are guided by the XAUI electrical interface specified in Clause 47 of IEEE 802.3ae-2002.

XAUI has similar application goals to serial RapidIO. The goal of this standard is that electrical designs for serial RapidIO can reuse electrical designs

for XAUI, suitably modified for applications at the baud intervals and reaches described herein.

Transmitter Specifications

LP-Serial transmitter electrical and timing specifications are stated in the text and tables of this section.

A Volts

B Volts

TD or RD

TD or RD

Differential Peak-Peak = 2 * (A – B)