LTC1403-1 Datasheet, PDF (10/20 Pages) Linear Technology – Serial 12-Bit/14-Bit, 2.8Msps Sampling ADCs with Shutdown

LTC1403-1/LTC1403A-1
APPLICATIO S I FOR ATIO
DRIVING THE ANALOG INPUT
The differential analog inputs of the LTC1403-1/LTC1403A-1
are easy to drive. The inputs may be driven differentially or as
a single-ended input (i.e., the A_IN– input is set to V_CM). Both
differential analog inputs, A_IN+ with A_IN–, are sampled 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 charging the sample-and-hold
capacitors at the end of conversion. During conversion, the
analog inputs draw only a small leakage current. If the source
impedance of the driving circuit is low, then the LTC1403-1/
LTC1403A-1 inputs can be driven directly. As source imped-
ance increases, so will acquisition time. For minimum acqui-
sition 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 har-
monic 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 sam-
pling capacitor, choose an amplifier that has a low output
impedance (<100Ω) at the closed-loop bandwidth frequency.
For example, if an amplifier is used with a gain of 1 and has
a unity-gain bandwidth of 50MHz, then the output impedance
at 50MHz must be less than 100Ω. 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 increasing the time between
conversions. The best choice for an op amp to drive the
LTC1403-1/LTC1403A-1 will depend on the application. Gen-
erally, 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 LTC1403-1/LTC1403A-1.
(More detailed information is available in the Linear Technol-
ogy Databooks and our website at www.linear.com.)
LTC^®1566-1: Low Noise 2.3MHz Continuous Time Low-
Pass Filter.
LT1630: Dual 30MHz Rail-to-Rail Voltage FB Amplifier. 2.7V
to ±15V supplies. Very high A_VOL, 500µV offset and 520ns
settling to 0.5LSB for a 4V swing. THD and noise are –93dB
to 40kHz and below 1LSB to 320kHz (A_V = 1, 2V_P-P into 1kΩ,
V_S = 5V), making the part excellent for AC applications (to
1/3 Nyquist) where rail-to-rail performance 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_VOL, 1.5mV offset and 400ns
settling to 0.5LSB for a 4V swing. It is suitable for applica-
tions with a single 5V supply. THD and noise are
–93dB to 40kHz and below 1LSB to 800kHz (A_V = 1,
2V_P-P into 1kΩ, V_S = 5V), making the part excellent for AC
applications where rail-to-rail performance is desired. Quad
version is available as LT1633.
LT1813: Dual 100MHz 750V/µs 3mA Voltage Feedback
Amplifier. 5V to ±5V supplies. Distortion is –86dB to 100kHz
and –77dB to 1MHz with ±5V supplies (2V_P-P into 500Ω).
Excellent part for fast AC applications with ±5V␣ supplies.
LT1801: 80MHz GBWP, –75dBc at 500kHz, 2mA/Amplifier,
8.5nV/√Hz.
LT1806/LT1807: 325MHz GBWP, –80dBc Distortion at 5MHz,
Unity-Gain Stable, R-R In and Out, 10mA/Amplifier, 3.5nV/√Hz.
LT1810: 180MHz GBWP, –90dBc Distortion at 5MHz,
Unity-Gain Stable, R-R In and Out, 15mA/Amplifier, 16nV/√Hz.
LT1818/LT1819: 400MHz, 2500V/µs,9mA, Single/Dual Volt-
age Mode Operational Amplifier.
LT6200: 165MHz GBWP, –85dBc Distortion at 1MHz, Unity-
Gain Stable, R-R In and Out, 15mA/Amplifier,
0.95nV/√Hz.
LT6203: 100MHz GBWP, –80dBc Distortion at 1MHz,
Unity-Gain Stable, R-R In and Out, 3mA/Amplifier,
1.9nV/√Hz.
LT6600-10: Amplifier/Filter Differential In/Out with 10MHz
Cutoff.
14031f
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