LMH7324_14 Datasheet, PDF (18/30 Pages) Texas Instruments – Quad 700 ps High Speed Comparator with RSPECL Outputs

LMH7324
SNOSAZ2F – SEPTEMBER 2007 – REVISED JULY 2010
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Slew Rate Dispersion
The slew rate is another parameter that affects propagation delay. The higher the input slew rate, the faster the
input stage switches. (See Figure 24.)
+
0
time
-
Slew Rate Dispersion
+
Dispersion
0
time
-
Figure 24. Slew Rate Dispersion
A combination of overdrive and slew rate dispersion occurs when applying signals with different amplitudes at
constant frequency. A small amplitude will produce a small voltage change per time unit (dV/dt) but also a small
maximum switching current (overdrive) in the input transistors. High amplitudes produce a high dV/dt and a
bigger overdrive.
Common Mode Dispersion
Dispersion will also occur when changing the common mode level of the input signal. (See Figure 25.) When
V_REF is swept through the CMVR (Common Mode Voltage Range), it results in a variation of the propagation
delay time. This variation is called Common Mode Dispersion.
Vin cm
+
0 ^{Vin cm}
time
-
Common Mode Dispersion
+
Dispersion
0
time
-
Figure 25. Common Mode Dispersion
All of the dispersion effects described previously influence the propagation delay. In practice the dispersion is
often caused by a combination of more than one varied parameter.
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