LMH7322_14 Datasheet, PDF (18/33 Pages) Texas Instruments – Dual 700 ps High Speed Comparator with RSPECL Outputs

LMH7322
SNOSAU8H – MARCH 2007 – REVISED MAY 2011
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5V
+
2k5
Vin
IN+
10k
10k
VREF
+
IN- _1/2
LMH 7322
RHYS
Q
Levels:
VOH = 3.9V
Q ^{VOL = 3.5V}
10k
1k
5k
5k
Figure 25. Standard Setup
Delay and Dispersion
Comparators are widely used to connect the analog world to the digital one. The accuracy of a comparator is
dictated by its DC properties, such as offset voltage and hysteresis, and by its timing aspects, such as rise and
fall times and delay. For low frequency applications most comparators are much faster than the analog input
signals they handle. The timing aspects are less important here than the accuracy of the input switching levels.
The higher the frequencies, the more important the timing properties of the comparator become, because the
response of the comparator can make a noticeable change in critical parameters such as time frame or duty
cycle. A designer has to know these effects and has to deal with them. In order to predict what the output signal
will do, several parameters are defined which describe the behavior of the comparator. For a good understanding
of the timing parameters discussed in the following section, a brief explanation is given and several timing
diagrams are shown for clarification.
Propagation Delay
The propagation delay parameter is described in the Table 1 section. Due to this definition there are two
parameters, t_PDH and t_PDL (Figure 26). Both parameters do not necessarily have the same value. It is possible
that differences will occur due to a different response of the internal circuitry. As a derivative of this effect another
parameter is defined: Δt_PD. This parameter is defined as the absolute value of the difference between t_PDH and
t_PDL.
PW
80%
V_IN 50%
20%
t_PDH
80%
50%
20%
t_PDL
Output Q
80%
50%
20%
t_r
80%
50%
20%
t_f
Figure 26. Propagation Delay
18
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