Datasheet

DS89C387

SNLS101E –MAY 1995–REVISED APRIL 2013

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APPLICATION INFORMATION

SKEW

Skew may be thought of in a lot of different ways, the next few paragraphs should clarify what is represented by

“Skew” in the datasheet and how it is determined. Skew, as used in this databook, is the absolute value of a

mathematical difference between two propagation delays. This is commonly accepted throughout the

semiconductor industry. However, there is no standardized method of measuring propagation delay, from which

skew is calculated, of differential line drivers. Elucidating, the voltage level, at which propagation delays are

measured, on both input and output waveforms are not always consistant. Therefore, skew calculated in this

datasheet, may not be calculated the same as skew defined in another. This is important to remember whenever

making a skew comparison.

Skew may be calculated for the DS89C387, from many different propagation delay measurements. They may be

classified into three categories, single-ended, differential, and complementry. Single-ended skew is calculated

from t

PHL

and t

PLH

measurements (see Figure 9 and Figure 11). Differential skew is calculated from t

PHLD

and

PLHD

measurements (see Figure 12 and Figure 13). Complementry skew is calculated from t

PHL

and t

PLH

measurements (see Figure 14 and Figure 15).

Figure 8. (Circuit 1) – Circuits for Measuring Single-Ended Propagation Delays

(See Figure 11)

Figure 9. (Circuit 2) – Circuits for Measuring Single-Ended Propagation Delays

(See Figure 11)

Figure 10. Waveforms for Circuit 1 – Propagation Delay Waveforms for Circuit 1 and Circuit 2

(See Figure 9)

Figure 11. Waveforms for Circuit 2 – Propagation Delay Waveforms for Circuit 1 and Circuit 2

(See Figure 9)

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