Texas Instruments LMH7324 Quad 700ps High Speed Comparator with RSPECL Outputs Evaluation Board LMH7324EVAL/NOPB LMH7324EVAL/NOPB Datenbogen
Produktcode
LMH7324EVAL/NOPB
C3
above window
input signal
below window
in window
C1
C2
C4
freq C1: 20 MHz
freq C4: 10 MHz
freq C4: 10 MHz
C1
±
500 mV/DIV
C2
±
500 mV/DIV
C3
±
500 mV/DIV
C4
±
200 mV/DIV
Timebase: 50 ns/DIV
Trigger: C4
Trigger: C4
C3
above window
input signal
below window
in window
C1
C2
C4
freq C1: 9.485 MHz
freq C4: 4.923 MHz
freq C4: 4.923 MHz
C1
±
500 mV/DIV
C2
±
500 mV/DIV
C3
±
500 mV/DIV
C4
±
200 mV/DIV
Timebase: 50 ns/DIV
Trigger: C4
Trigger: C4
Measurement Hints and Results
Figure 3. 5 MHz Crossing Whole Window
Higher frequencies will make the pulses much shorter, especially when a sine wave is used and the signal
rises far above the window levels. This situation would make the time that the signal crosses the window
levels very short, because a sine wave has the highest dV/dt at the transition points.
rises far above the window levels. This situation would make the time that the signal crosses the window
levels very short, because a sine wave has the highest dV/dt at the transition points.
and
show the measurements taken when a sine wave is used. In
a sine wave of 10 MHz
is used and it just crosses both levels of the window. This creates a reasonable pulse width for both the
detection signals “above window” and “below window” and for the detection signal “in window.” The added
hysteresis works since no oscillations can be seen although the input signal crosses the levels very slowly
and with low overdrive. When using a signal with the same frequency but with a much greater amplitude,
the time it takes for the signal to cross the window becomes much shorter as can be seen in
detection signals “above window” and “below window” and for the detection signal “in window.” The added
hysteresis works since no oscillations can be seen although the input signal crosses the levels very slowly
and with low overdrive. When using a signal with the same frequency but with a much greater amplitude,
the time it takes for the signal to cross the window becomes much shorter as can be seen in
Note that the frequency of the detection signal “in window” doubles compared to the input frequency. Also
the crossing time through the window levels is very short and, for this example, it is equal to one period of
a frequency of 227 MHz (see marker indication in plot). This means that the detection signal “in window” is
the most critical of the three detection signals and will be the first to incur problems due to frequency
limits. The setup of
the crossing time through the window levels is very short and, for this example, it is equal to one period of
a frequency of 227 MHz (see marker indication in plot). This means that the detection signal “in window” is
the most critical of the three detection signals and will be the first to incur problems due to frequency
limits. The setup of
uses an input frequency of 100 MHz with a big overdrive at the window
levels. This results in a very small pulse for the detection signal “in window” which is equal to one period
of a 1.05 GHz signal (see markers indication in plot). All signals are measured using a cable with a length
of 1 meter connected to a four channel oscilloscope. All channels are AC coupled and terminated with
50
of a 1.05 GHz signal (see markers indication in plot). All signals are measured using a cable with a length
of 1 meter connected to a four channel oscilloscope. All channels are AC coupled and terminated with
50
Ω
.
Figure 4. 10 MHz Just Above Thresholds
4
AN-1683 LMH7324 High Speed Comparator Evaluation Board
SNOA494A – September 2007 – Revised May 2013
Copyright © 2007–2013, Texas Instruments Incorporated