LTC1407 LINER [Linear Technology], LTC1407 Datasheet - Page 11

• Manufacturer Part Number: LTC1407
• Description: Serial 12-Bit/14-Bit, 3Msps Simultaneous Sampling Simultaneous Sampling
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
DRIVING THE ANALOG INPUT
The differential analog inputs of the LTC1407/LTC1407A
are easy to drive. The inputs may be driven differentially or
as a single-ended input (i.e., the CH0
All four analog inputs of both differential analog input
pairs, CH0
at the same instant. Any unwanted signal that is common
to both inputs of each input pair will be reduced by the
common mode rejection of the sample-and-hold circuit.
The inputs draw only one small current spike while charg-
ing the sample-and-hold capacitors at the end of conver-
sion. During conversion, the analog inputs draw only a
small leakage current. If the source impedance of the
driving circuit is low, then the LTC1407/LTC1407A inputs
can be driven directly. As source impedance increases, so
will acquisition time. For minimum acquisition time with
high source impedance, a buffer amplifier must be used.
The main requirement is that the amplifier driving the
analog input(s) must settle after the small current spike
before the next conversion starts (settling time must be
39ns for full throughput rate). Also keep in mind, while
choosing an input amplifier, the amount of noise and
harmonic distortion added by the amplifier.
CHOOSING AN INPUT AMPLIFIER
Choosing an input amplifier is easy if a few requirements
are taken into consideration. First, to limit the magnitude
of the voltage spike seen by the amplifier from charging
the sampling capacitor, choose an amplifier that has a low
output impedance (< 100 ) at the closed-loop bandwidth
frequency. For example, if an amplifier is used in a gain of
1 and has a unity-gain bandwidth of 50MHz, then the
output impedance at 50MHz must be less than 100 . The
second requirement is that the closed-loop bandwidth
must be greater than 40MHz to ensure adequate small-
signal settling for full throughput rate. If slower op amps
are used, more time for settling can be provided by
+
with CH0
U
–
and CH1
U
+
with CH1
W
–
input is grounded).
–
, are sampled
U
increasing the time between conversions. The best choice
for an op amp to drive the LTC1407/LTC1407A depends
on the application. Generally, applications fall into two
categories: AC applications where dynamic specifications
are most critical and time domain applications where DC
accuracy and settling time are most critical. The following
list is a summary of the op amps that are suitable for
driving the LTC1407/LTC1407A. (More detailed informa-
tion is available in the Linear Technology Databooks and
on the LinearView
LTC1566-1: Low Noise 2.3MHz Continuous Time Low-
pass Filter.
LT
2.7V to 15V supplies. Very high A
520ns settling to 0.5LSB for a 4V swing. THD and noise
are – 93dB to 40kHz and below 1LSB to 320kHz (A
2V
applications (to 1/3 Nyquist) where rail-to-rail perfor-
mance is desired. Quad version is available as LT1631.
LT1632: Dual 45MHz Rail-to-Rail Voltage FB Amplifier.
2.7V to 15V supplies. Very high A
400ns settling to 0.5LSB for a 4V swing. It is suitable for
applications with a single 5V supply. THD and noise are
– 93dB to 40kHz and below 1LSB to 800kHz (A
2V
applications where rail-to-rail performance is desired.
Quad version is available as LT1633.
LT1801: 80MHz GBWP, –75dBc at 500kHz, 2mA/ampli-
fier, 8.5nV/ Hz.
LT1806/LT1807: 325MHz GBWP, –80dBc distortion at
5MHz, unity gain stable, rail-to-rail in and out,
10mA/amplifier, 3.5nV/ Hz.
LT1810: 180MHz GBWP, –90dBc distortion at 5MHz,
unity gain stable, rail-to-rail in and out, 15mA/amplifier,
16nV/ Hz.
LinearView is a trademark of Linear Technology Corporation.
®
P-P
P-P
1630: Dual 30MHz Rail-to-Rail Voltage FB Amplifier.
into 1k , V
into 1k , V
S
S
TM
= 5V), making the part excellent for AC
= 5V), making the part excellent for AC
CD-ROM.)
LTC1407/LTC1407A
VOL
VOL
, 1.5mV offset and
, 500 V offset and
11
V
V
= 1,
= 1,
1407f