LT1719 Linear Technology, LT1719 Datasheet - Page 16

• Manufacturer Part Number: LT1719
• Description: 4ns/ 150MHz Dual Comparator with Independent Input/Output Supplies
• Manufacturer: Linear Technology

LT1719
High Performance Sine Wave
to Square Wave Converter
Propagation delay of comparators is typically specified for
a 100mV step with some fraction of that for overdrive. But
in many signal processing applications, such as in com-
munications, the goal is to convert a sine wave, such as a
carrier, to a square wave for use as a timing clock. The
desired behavior is for the output timing to be dependent
on the input timing only. No phase shift should occur as a
function of the input amplitude, which would result in AM
to FM conversion.
The circuit of Figure 8a is a simple LT1719-based sine
wave to square wave converter. The 5V supplies on the
input allow very large swing inputs, while the 3V logic
supply keeps the output swing small to minimize cross
talk. Figure 8b shows the time delay vs input amplitude
with a 10MHz sine wave. The LT1719 delay changes just
0.65ns over the 26dB amplitude range; 2.33 at 10MHz.
The delay is particularly flat yielding excellent AM rejection
16
TYPICAL
RELATED PARTS
PART NUMBER
LT1016
LT1116
LT1394
LT1671
LT1720/LT1721
Figure 8a. LT1719-Based Sine Wave to Square Wave Converter
SINE WAVE
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] FAX: [phone] www.linear-tech.com
INPUT
APPLICATION
50
DESCRIPTION
UltraFast Precision Comparator
12ns Single Supply Ground-Sensing Comparator
7ns, UltraFast, Single Supply Comparator
60ns, Low Power, Single Supply Comparator
Dual/Quad 4.5ns, Single Supply 3V/5V Comparator
+
–
–5V
5V
LT1719
3V
U
SQUARE WAVE
OUTPUT
1719 F08a
from 0dBm to 15dBm. If a 2:1 transformer is used to drive
the input differentially, this exceptionally flat zone spans
– 5dBm to 10dBm, a common range for RF signal levels.
Similar delay performance is achieved with input frequen-
cies as high as 50MHz. There is, however, some additional
encroachment into the central flat zone by both the small
amplitude and large amplitude variations.
With small input signals, the hysteresis and dispersion
make the LT1719 act like a comparator with a 12mV
hysteresis span. In other words, a 12mV
10MHz will barely toggle the LT1719, with 90 of phase lag
or 25ns additional delay.
Above 5V
crease due to internal capacitive feed-forward in the input
stage. Unlike some comparators, the LT1719 will not
falsely anticipate a change in input polarity, but the feed-
forward is enough to make a transition propagate through
the LT1719 faster once the input polarity does change.
Figure 8b. Time Delay vs Sine Wave Input Amplitude
P-P
5
4
3
2
1
0
Industry Standard 10ns Comparator
Dual/Quad Comparator Similar to the LT1719
COMMENTS
Single Supply Version of LT1016
6mA Single Supply Comparator
450 A Single Supply Comparator
–5
at 10MHz, the LT1719 delay starts to de-
25 C
V
V
+V
10MHz
632mV
CC
EE
S
= – 5V
= 5V
= 3V
0
P-P
INPUT AMPLITUDE (dBm)
5
2V
10
P-P
LINEAR TECHNOLOGY CORPORATION 2000
1719f LT/TP 0300 4K • PRINTED IN USA
15
6.32V
20
P-P
1719 F08b
P-P
25
sine wave at