OMO ElectronicOMO Electronic
Expand menu
Hello, Sign inMy Account
0 Cart

LTC1417ACGN#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P32
10
LTC1417
sn1417 1417fas
Signal-to-Noise Ratio
The signal-to-noise plus distortion ratio [S/(N + D)] is the
ratio between the RMS amplitude of the fundamental input
frequency to the RMS amplitude of all other frequency
components at the A/D output. The output is band limited
to frequencies from above DC and below half the sampling
frequency. Figure 3b shows a typical spectral content with
a 400kHz sampling rate and a 200kHz input. The dynamic
performance is excellent for input frequencies up to and
beyond the Nyquist limit of 200kHz.
Figure 4. Effective Bits and Signal/(Noise + Distortion)
vs Input Frequency
APPLICATIONS INFORMATION
WUU
U
Figure 3a. LTC1417 Nonaveraged, 4096 Point FFT,
Input Frequency = 10kHz
Figure 3b. LTC1417 Nonaveraged, 4096 Point FFT,
Input Frequency = 200kHz
FREQUENCY (kHz)
0 10050
AMPLITUDE (dB)
0
–20
–40
–60
–80
–100
–120
150
1417 G07
200
f
SAMPLE
= 400kHz
f
IN
= 10.05859375kHz
SFDR = –97.44dB
SINAD = 81.71dB
FREQUENCY (kHz)
0 50 100
AMPLITUDE (dB)
0
–20
–40
–60
–80
–100
–120
150
1417 G08
200
f
SAMPLE
= 400kHz
f
IN
= 197.949188kHz
SFDR = –98dB
SINAD = 81.1dB
Effective Number of Bits
The effective number of bits (ENOBs) is a measurement of
the resolution of an ADC and is directly related to the
S/(N + D) by the equation:
ENOB (N) = [S/(N + D) – 1.76]/6.02
where N is the effective number of bits of resolution and
S/(N + D) is expressed in dB. At the maximum sampling
rate of 400kHz, the LTC1417 maintains near ideal ENOBs
up to the Nyquist input frequency of 200kHz (refer to
Figure 4).
INPUT FREQUENCY (Hz)
4
EFFECTIVE BITS
S/(N + D) (dB)
6
8
10
12
10k 100k 1M
1417 TA02
2
1k
14 86
80
74
68
62
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS
sum of all harmonics of the input signal to the fundamental
itself. The out-of-band harmonics alias into the frequency
band between DC and half the sampling frequency. THD is
expressed as:
THD Log
VVV Vn
V
=
+++
20
234
1
222 2
...
where V1 is the RMS amplitude of the fundamental fre-
quency and V2 through Vn are the amplitudes of the
second through nth harmonics. THD vs Input Frequency is
shown in Figure 5. The LTC1417 has good distortion
performance up to the Nyquist frequency and beyond.
11
LTC1417
sn1417 1417fas
Intermodulation Distortion
If the ADC input signal consists of more than one spectral
component, the ADC transfer function nonlinearity can
produce intermodulation distortion (IMD) in addition to
THD. IMD is the change in one sinusoidal input caused by
the presence of another sinusoidal input at a different
frequency.
If two pure sine waves of frequencies fa and fb are applied
to the ADC input, nonlinearities in the ADC transfer func-
tion can create distortion products at the sum and differ-
ence frequencies of mfa ±nfb, where m and n = 0, 1, 2, 3,
etc. For example, 2nd order IMD terms include (fa ± fb). If
the two input sine waves are equal in magnitude, the value
(in decibels) of the 2nd-order IMD products can be
expressed by the following formula:
IMD fa fb Log
Amplitude
+
()
=
±
()
20
at fa fb
Amplitude at fa
Peak Harmonic or Spurious Noise
The peak harmonic or spurious noise is the largest spec-
tral component excluding the input signal and DC. This
value is expressed in decibels relative to the RMS value of
a full-scale input signal.
Full-Power and Full-Linear Bandwidth
The full-power bandwidth is the input frequency at which
the amplitude of the reconstructed fundamental is
reduced by 3dB from a full-scale input signal.
The full-linear bandwidth is the input frequency at which
the S/(N + D) has dropped to 77dB (12.5 effective bits).
The LTC1417 has been designed to optimize input band-
width, allowing the ADC to undersample input signals with
frequencies above the converter’s Nyquist Frequency. The
noise floor stays very low at high frequencies; S/(N + D)
becomes dominated by distortion at frequencies far
beyond Nyquist.
DRIVING THE ANALOG INPUT
The differential analog inputs of the LTC1417 are easy to
drive. The inputs may be driven differentially or as a single-
ended input (i.e., the A
IN
–
input is grounded). The A
IN
+
and
A
IN
–
inputs are sampled at the same instant. Any
unwanted signal that is common to both inputs 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 LTC1417
inputs can be driven directly. As source impedance
increases, so will acquisition time (see Figure 7). For
minimum acquisition time, with high source impedance, a
buffer amplifier must be used. The only requirement is that
the amplifier driving the analog input(s) must settle after
the small current spike before the next conversion starts —
500ns for full throughput rate.
APPLICATIONS INFORMATION
WUU
U
Figure 5. Distortion vs Input Frequency
INPUT FREQUENCY (kHz)
1
–120
AMPLITUDE (dB BELOW THE FUNDAMENTAL)
–100
–80
–60
–40
0
10 100
THD
2ND
3RD
1417 G05
1000
–20
Figure 6. Intermodulation Distortion Plot
FREQUENCY (kHz)
0
–120
AMPLITUDE (dB)
–100
–80
–60
–40
40 100
140
200
1417 G09
–20
0
20 60 80
120
160 180
f
SAMPLE
= 400kHz
f
IN1
= 97.303466kHz
f
IN2
= 104.632568kHz
V
IN
= 4.096V
P-P
12
LTC1417
sn1417 1417fas
LT1360: 50MHz Voltage Feedback Amplifier. 3.8mA sup-
ply current, ±2.5V to ±15V supplies. High A
VOL
, 1mV
offset and 80ns settling to 1mV (4V step, inverting and
noninverting configurations) make it suitable for fast DC
applications. Excellent AC specifications. Dual and quad
versions are available as LT1361 and LT1362.
LT1468: 90MHz Voltage Feedback Amplifier. ±5V to ±15V
supplies. Lower distortion and noise. Settles to 0.01% in
770ns. Distortion is –115dB to 20kHz.
LT1498/LT1499: 10MHz, 6V/µs, Dual/Quad Rail-to-Rail
Input and Output Op Amps. 1.7mA supply current per
amplifier. 2.2V to ±15V supplies. Good AC performance,
input noise voltage = 12nV/√Hz (typ).
LT1630/LT1631: 30MHz, 10V/µs, Dual/Quad Rail-to-Rail
Input and Output Precision Op Amps. 3.5mA supply
current per amplifier. 2.7V to ±15V supplies. Best AC
performance, input noise voltage = 6nV/√Hz (typ),
THD = –86dB at 100kHz.
LT1813: Dual 100MHz 750V/µs 3mA VFA. 5V to ±5V
supplies. Distortion is –86dB to 100kHz and –77dB to
1MHz with ±5V supplies (2V
P-P
into 500Ω). Great part for
fast AC applications with ±5V supplies.
Input Filtering
The noise and the distortion of the input amplifier and
other circuitry must be considered since they will add to
the LTC1417 noise and distortion. The small-signal band-
width of the sample-and-hold circuit is 10MHz. Any noise
or distortion products that are present at the analog inputs
will be summed over this entire bandwidth. Noisy input
circuitry should be filtered prior to the analog inputs to
minimize noise. A simple 1-pole RC filter is sufficient for
many applications. For example, Figure 8 shows a 1000pF
APPLICATIONS INFORMATION
WUU
U
LinearView is a trademark of Linear Technology Corporation.
Figure 7. t
ACQ
vs Source Resistance
SOURCE RESISTANCE (Ω)
0.1
ACQUISITION TIME (µs)
10
1
1 100 1k 10k
1417 F07
0.01
10
100
100k
Choosing an Input Amplifier
Choosing an input amplifier is easy if a few requirements
are taken into consideration. First, choose an amplifier that
has a low output impedance (<100Ω) at the closed-loop
bandwidth frequency. For example, if an amplifier is used
in a gain of 1 and has a closed-loop bandwidth of 10MHz,
then the output impedance at 10MHz must be less than
100Ω. The second requirement is that the closed-loop
bandwidth must be greater than 10MHz to ensure ad-
equate small-signal settling for full throughput rate. If
slower op amps are used, more settling time can be
provided by increasing the time between conversions.
The best choice for an op amp to drive the LTC1417 will
depend on the application. Generally, applications fall into
two categories: AC applications where dynamic specifica-
tions 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 LTC1417. More detailed information is
available in the Linear Technology Databooks and on the
LinearView
TM
CD-ROM.
LT
®
1354: 12MHz, 400V/µs Op Amp. 1.25mA maximum
supply current. Good AC and DC specifications. Suitable
for dual supply application.
LT1357: 25MHz, 600V/µs Op Amp. 2.5mA maximum
supply current. Good AC and DC specifications. Suitable
for dual supply application.
Figure 8. RC Input Filter
LTC1417
A
IN
+
A
IN
–
V
REF
REFCOMP
AGND
ANALOG INPUT
100Ω
1417 F08
1
2
3
4
5
1000pF
10µF
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P32

LTC1417ACGN#TRPBF

Mfr. #:
Buy LTC1417ACGN#TRPBF
Manufacturer:
Analog Devices Inc.
Description:
Analog to Digital Converters - ADC L Pwr 14-B, 400ksps Smpl ADC Conv w/ Ser
Lifecycle:
New from this manufacturer.
Delivery:
DHL FedEx Ups TNT EMS
Payment:
T/T Paypal Visa MoneyGram Western Union

Products related to this Datasheet