LTC1401 查看數據表（PDF） - Linear Technology
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LTC1401 Datasheet PDF : 20 Pages
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LTC1401
APPLICATIONS INFORMATION
0
–10
–20
fSAMPLE = 200kHz
fIN = 99.072266kHz
SINAD = 65dB
–30 THD = –66dB
–40
VCC = 3V
TA = 25°C
–50
– 60
–70
–80
–90
–100
–110
–120
0 10 20 30 40 50 60 70 80 90 100
FREQUENCY (kHz)
LTC1400 • F02b
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 = 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. Figure 3 shows ENOBs vs
Input Frequency.
12
11
10
9
8
7
6
5
4
3
2
1
TA = 25°C
fSAMPLE = 200kHz
0
10k
100k
INPUT FREQUENCY (Hz)
74
68
62
56
50
1M
LTC1401 • F03
Figure 3. Effective Bits and Signal-to-Noise +
Distortion vs Input Frequency
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
V1
+
...Vn2
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.
0
TA = 25°C
–10 fSAMPLE = 200kHz
–20
–30
–40
–50
2ND HARMONIC
–60
THD
–70
–80
3RD HARMONIC
–90
–100
10k
100k
INPUT FREQUENCY (Hz)
1M
LTC1401 • F04
Figure 4. Distortion vs Input Frequency
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-
8
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