LMH7322 Datasheet, PDF (20/33 Pages) Texas Instruments – Dual 700 ps High Speed Comparator with RSPECL Outputs

LMH7322
SNOSAU8I – MARCH 2007 – REVISED MARCH 2013
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Overdrive 100 mV
+
Overdrive 10 mV
0
time
-100 mV
-
Overdrive Dispersion
+
Dispersion
0
time
-
Figure 28. Overdrive Dispersion
The overdrive dispersion is caused by the switching currents in the input stage which is dependent on the level of
the differential input signal.
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 29).
+
0
time
-
Slew Rate Dispersion
+
Dispersion
0
time
-
Figure 29. 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
larger overdrive.
Common Mode Dispersion
Dispersion will also occur when changing the common mode level of the input signal (Figure 30). 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.
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