DS89C386 Datasheet, PDF (6/10 Pages) National Semiconductor (TI) – Twelve Channel CMOS Differential Line Receiver

Application Information (Continued)
(Circuit 1)
(Circuit 2)
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FIGURE 5. Circuits for Measuring Single-Ended Propagation Delays (See Figure 6)
Waveforms for Circuit 1
Waveforms for Circuit 2
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FIGURE 6. Propagation Delay Waveforms for Circuit 1 and Circuit 2 (See Figure 5)
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In Figure 6, VX, where X is a number, is the waveform volt-
age level at which the propagation delay measurement ei-
ther starts or stops. Furthermore, V1 and V2 are normally
identical. The same is true for V3 and V4. However, as men-
tioned before, these levels are not standardized and may
vary, even with similar devices from other companies. Also
note, V_REF in Figure 1 should equal V1 and V2 in Figure 6.
The single-ended skew provides information about the pulse
width distortion of the output waveform. The lower the skew,
the less the output waveform will be distorted. For best case,
skew would be zero, and the output duty cycle would be
50%, assuming the input has a 50% duty cycle.
(Circuit 3)
Waveforms for Circuit 3
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FIGURE 7. Circuit for Measuring Differential
Propagation Delays (See Figure 8)
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FIGURE 8. Propagation Delay Waveforms
for Circuit 3 (see Figure 7)
For differential propagation delays, V1 may not equal V2.
Furthermore, the crossing point of RI and RI* corresponds to
zero volts on the differential waveform. (See middle wave-
form in Figure 8.) This is true whether V1 equals V2 or not.
However, if V1 and V2 are specified voltages, then V1 and
V2 are less likely to be equal to the crossing point voltage.
Thus, the differential propagation delays will not be mea-
sured from zero volts on the differential waveform.
The differential skew also provides information about the
pulse width distortion of the output waveform relative to the
differential input waveform. The higher the skew, the greater
the distortion of the output waveform. Assuming the differen-
tial input has a 50% duty cycle, the output will have a 50%
duty cycle if skew equals zero and less than a 50% duty
cycle if skew is greater than zero.
Only t_SK is specified in this datasheet for the DS89C386. t_SK
is measured singIe-endedly but corresponds to differential
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