Datasheet

LTC1407/LTC1407A
12
1407fb
APPLICATIONS INFORMATION
LT1818/LT1819: 400MHz, 2500V/µs, 9mA, Single/Dual
Voltage Mode Operational Amplifi er.
LT6200: 165MHz GBWP, –85dBc distortion at 1MHz,
unity-gain stable, rail-to-rail in and out, 15mA/amplifi er,
0.95nV/√Hz.
LT6203: 100MHz GBWP, –80dBc distortion at 1MHz,
unity-gain stable, rail-to-rail in and out, 3mA/amplifi er,
1.9nV/√Hz.
LT6600: Amplifi er/Filter Differential In/Out with 10MHz
Cutoff.
INPUT FILTERING AND SOURCE IMPEDANCE
The noise and the distortion of the input amplifi er and
other circuitry must be considered since they will add to
the LTC1407/LTC1407A noise and distortion. The small-
signal bandwidth of the sample-and-hold circuit is 50MHz.
Any noise or distortion products that are present at the
analog inputs will be summed over this entire bandwidth.
Noisy input circuitry should be fi ltered prior to the analog
Figure 1. RC Input Filter
inputs to minimize noise. A simple 1-pole RC fi lter is
suffi cient for many applications. For example, Figure 1
shows a 47pF capacitor from CHO
+
to ground and a 51
source resistor to limit the net input bandwidth to 30MHz.
The 47pF capacitor also acts as a charge reservoir for the
input sample-and-hold and isolates the ADC input from
sampling-glitch sensitive circuitry. High quality capacitors
and resistors should be used since these components
can add distortion. NPO and silvermica type dielectric
capacitors have excellent linearity. Carbon surface mount
resistors can generate distortion from self heating and
from damage that may occur during soldering. Metal
fi lm surface mount resistors are much less susceptible
to both problems. When high amplitude unwanted signals
are close in frequency to the desired signal frequency a
multiple pole fi lter is required.
High external source resistance, combined with 13pF
of input capacitance, will reduce the rated 50MHz input
bandwidth and increase acquisition time beyond 39ns.
LTC1407/
LTC1407A
CH0
+
CH0
–
V
REF
GND
1407 F01
1
2
11
3
10µF
47pF*
51*
CH1
+
CH1
–
4
5
47pF*
*TIGHT TOLERANCE REQUIRED TO AVOID
APERTURE SKEW DEGRADATION
51*
ANALOG
INPUT
ANALOG
INPUT