LMH7324_14 Datasheet, PDF (17/30 Pages) Texas Instruments – Quad 700 ps High Speed Comparator with RSPECL Outputs

LMH7324
www.ti.com
SNOSAZ2F – SEPTEMBER 2007 – REVISED JULY 2010
Both output circuits should be symmetrical. At the moment one output is switching ‘on’ the other is switching ‘off’
with ideally no skew between both outputs. The design of the LMH7324 is optimized so that this timing difference
is minimized. The propagation delay, t_PD, is defined as the average delay of both outputs at both slopes: (t_PDLH +
t_PDHL)/2. Both overdrive and starting point should be equally divided around the V_REF (absolute values).
DISPERSION
There are several circumstances that will produce a variation of the propagation delay time. This effect is called
dispersion.
Amplitude Overdrive Dispersion
One of the parameters that causes dispersion is the amplitude variation of the input signal. Figure 23 shows the
dispersion due to a variation of the input overdrive voltage. The overdrive is defined as the ‘go to’ differential
voltage applied to the inputs. Figure 23 shows the impact it has on the propagation delay time if the overdrive is
varied from 10 mV to 100 mV. This parameter is measured with a constant slew rate of the input signal.
+
Overdrive 100 mV
Overdrive 10 mV
0
time
-100 mV
-
Overdrive Dispersion
+
Dispersion
0
time
-
Figure 23. Overdrive Dispersion
The overdrive dispersion is caused by the switching currents in the input stage which are dependent on the level
of the differential input signal.
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