ADCMP572BCP AD [Analog Devices], ADCMP572BCP Datasheet - Page 10

• Manufacturer Part Number: ADCMP572BCP
• Description: Ultrafast 3.3 V Single-Supply Comparators
• Manufacturer: AD [Analog Devices]

ADCMP572/ADCMP573
external 500 Ω resistor, and leaving the LE pin disconnected. In
this case, the resistor value does not depend on the chosen V
supply voltage, assuming the V
V
OPTIMIZING HIGH SPEED PERFORMANCE
As with any high speed comparator, proper design and layout
techniques are essential to obtaining the specified performance.
Stray capacitance, inductance, inductive power and ground
impedances, or other layout issues can severely limit performance
and can often cause oscillation. Discontinuities along input and
output transmission lines can also severely limit the specified
pulse-width dispersion performance.
For applications working in a 50 Ω environment, input and
output matching has a significant impact on data dependant (or
deterministic) jitter (DJ) and pulse-width dispersion perform-
ance. The ADCMP572/ADCMP573 comparators provide
internal 50 Ω termination resistors for both V
and the ADCMP572 provides 50 Ω back terminated outputs.
The return side for each input termination is pinned out
separately with the V
termination is desired at one or both of the V
the V
(from) the desired termination potential as required. The
termination potential should be carefully bypassed using high
quality bypass capacitors as discussed above to prevent undesired
aberrations on the input signal due to parasitic inductance in
the circuit board layout. If a 50 Ω input termination is not
desired, either one or both of the V
be left disconnected. In this case, the pins should be left floating
with no external pull-downs or bypassing capacitors.
It should be understood that when leaving an input termination
disconnected, the internal resistor acts as a small stub on the
input transmission path and can cause problems for very high
speed inputs. Reflections should then be expected from the
comparator inputs because they no longer provide a matched
impedance to the input path leading to the device. It then
becomes important to back-match the drive source impedance
to the input transmission path to minimize multiple reflections.
For applications in which the comparator is very close to the
driving signal source, the source impedance should be mini-
mized. High source impedance in combination with parasitic
input capacitance of the comparator could cause an undesirable
degradation in bandwidth at the input, thus degrading the overall
response. Although the ADCMP572/ ADCMP573 comparators
have been designed to minimize input capacitance, some parasitic
capacitance is inevitable. It is therefore recommended that the
drive source impedance be no more than 50 Ω for best high
speed performance.
CCO
– 2 V.
TP
and V
TN
pins can be connected (or disconnected) to
TP
and V
TN
TT
pins, respectively. If a 50 Ω
pin is properly connected to
TP
/V
TN
termination pins can
P
P
/V
and V
N
inputs, then
N
inputs,
Rev. PrB | Page 10 of 16
CCO
COMPARATOR PROPAGATION
DELAY DISPERSION
The ADCMP572/ADCMP573 comparators are designed to
reduce propagation delay dispersion over a wide input overdrive
range of 5 mV to 500 mV. Propagation delay dispersion is a
variation in propagation delay that results from a change in the
degree of overdrive or slew rate (how far or how fast the input
signal exceeds the switching threshold).
Propagation delay dispersion is a specification that becomes
important in high speed time critical applications such as data
communication, automatic test and measurement, instrumenta-
tion, and event-driven applications such as pulse spectroscopy,
nuclear instrumentation, and medical imaging. Dispersion is
defined as the variation in propagation delay as the input over-
drive conditions are changed (Figure 14 and Figure 15). For the
ADCMP572/ADCMP573, dispersion is typically <15 ps because
the overdrive is varied from 10 mV to 500 mV, and the input
slew rate is varied from 2 V/ns to 10 V/ns. This specification
applies for both positive and negative signals since the
ADCMP572/ADCMP573 has substantially equal delays for
either positive-going or negative-going inputs.
INPUT VOLTAGE
Q/Q OUTPUT
INPUT VOLTAGE
Q/Q OUTPUT
Figure 14. Propagation Delay—Overdrive Dispersion
Figure 15. Propagation Delay—Slew Rate Dispersion
Preliminary Technical Data
10V/ns
1V/ns
500mV OVERDRIVE
10mV OVERDRIVE
DISPERSION
DISPERSION
V
V
N
N
± V
± V
OS
OS