LT1720 Linear Technology, LT1720 Datasheet - Page 21

• Manufacturer Part Number: LT1720
• Description: 4ns/ 150MHz Dual Comparator with Independent Input/Output Supplies
• Manufacturer: Linear Technology

APPLICATIONS
and 100 V/ C baseline uncertainty. Switching delay is
less than 15ns and the minimum sampling window width
for full power response is 30ns.
The input waveform is presented to the diode bridge
switch, the output of which feeds the LT1227 wideband
amplifier. The LT1720 comparators, triggered by the sample
command, generate phase-opposed outputs. These sig-
nals are level shifted by the transistors, providing comple-
mentary bipolar drive to switch the bridge. A skew
compensation trim ensures bridge-drive signal simulta-
neity within 1ns. The AC balance corrects for parasitic
capacitive bridge imbalances. A DC balance adjustment
trims bridge offset.
The trim sequence involves grounding the input via 50
and applying a 100kHz sample command. The DC balance
CLOCK
INPUT
** SUMIDA CD43-100
* 1% FILM RESISTOR
†
U
POLYSTYRENE, 5%
= 1N4148
= 74HC04
INFORMATION
U
“FIXED”
TRIM
10ns
W
0V TO 2V
Figure 18. Voltage-Controlled Clock Skew
2k*
2k
INPUT
SKEW
12pF
10ns
“SKEWED”
VARACTOR
†
MV-209
U
DIODE
14k
+
–
LT1077
0.005 F
A1
2.5k*
36pF
†
is adjusted for minimal bridge ON vs OFF variation at the
output. The skew compensation and AC balance adjust-
ments are then optimized for minimum AC disturbance in
the output. Finally, unground the input and the circuit is
ready for use.
Voltage-Controlled Clock Skew Generator
It is sometimes necessary to generate pairs of identical
clock signals that are phase skewed in time. Further, it is
desirable to be able to set the amount of time skew via a
tuning voltage. Figure 18’s circuit does this by utilizing
the LT1720 to digitize phase information from a varactor-
tuned time domain bridge. A 0V to 2V control signal
provides
from a 2.7V to 6V supply.
1M
6.2M*
1.82M*
1M
2.2 F
V
CC
0.1 F
+
–
+
–
1/2 LT1720
+
1/2 LT1720
10ns of output skew. This circuit operates
2.7V TO 6V
C2
C1
V
CC
V
V
IN
C
V
200pF
LT1317
CC
L1**
2.5k
2.5k
GND
SW
FB
LT1720/LT1721
Q
Q
FIXED
OUTPUT
SKEWED
OUTPUT
47 F
1720/21 F18
1.1M
100k
21