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LTC1401I Datasheet(PDF) 8 Page - Linear Technology

Part No. LTC1401I
Description  Complete SO-8, 12-Bit, 200ksps ADC with Shutdown
Download  20 Pages
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Maker  LINER [Linear Technology]
Homepage  http://www.linear.com
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LTC1401I Datasheet(HTML) 8 Page - Linear Technology

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8
LTC1401
APPLICATIONS INFORMATION
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 of the sampling frequency. THD
is expressed as:
THD = 20log
V22 + V32 + ...Vn2
V1
Where V1 is the RMS amplitude of the fundamental
frequency and V2 through Vn are the amplitudes of the
second through nth harmonics. THD vs input frequency is
shown in Figure 4. The LTC1401 has good distortion
performance up to the Nyquist frequency and beyond.
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
function can create distortion products at sum and differ-
FREQUENCY (kHz)
020
40
50
70
90
10
30
60
80
100
LTC1400 • F02b
0
–10
–20
–30
–40
–50
– 60
–70
–80
–90
–100
–110
–120
fSAMPLE = 200kHz
fIN = 99.072266kHz
SINAD = 65dB
THD = –66dB
VCC = 3V
TA = 25°C
INPUT FREQUENCY (Hz)
10k
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
100k
1M
LTC1401 • F04
2ND HARMONIC
THD
3RD HARMONIC
TA = 25°C
fSAMPLE = 200kHz
Figure 4. Distortion vs Input Frequency
Figure 2b. LTC1401 Nonaveraged, 4096 Point FFT
Plot with 100kHz Input Frequency
Effective Number of Bits
The effective number of bits (ENOBs) is a measurement of
the effective resolution of an ADC and is directly related to
the S/(N + D) by the equation:
N
SN D
=
+
()
/– .
.
176
602
where N is the effective number of bits of resolution and
S/(N + D) is expressed in dB. Figure 3 shows ENOBs vs
Input Frequency.
Figure 3. Effective Bits and Signal-to-Noise +
Distortion vs Input Frequency
INPUT FREQUENCY (Hz)
10k
12
11
10
9
8
7
6
5
4
3
2
1
0
74
68
62
56
50
100k
1M
LTC1401 • F03
TA = 25°C
fSAMPLE = 200kHz


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