LTC1416 Ver la hoja de datos (PDF) - Linear Technology
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LTC1416 Datasheet PDF : 20 Pages
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LTC1416
APPLICATIONS INFORMATION
DYNAMIC PERFORMANCE
The LTC1416 has excellent high speed sampling capabil-
ity. FFT (Fast Fourier Transform) test techniques are used
to test the ADC’s frequency response, distortion and noise
at the rated throughput. By applying a low distortion sine
wave and analyzing the digital output using an FFT algo-
rithm, the ADC’s spectral content can be examined for
frequencies outside the fundamental. Figure 2 shows a
typical LTC1416 FFT plot.
0
fSAMPLE = 400kHz
–20
fIN = 101.5625kHz
SFDR = 95.2dB
SINAD = 80.5dB
–40
–60
–80
–100
–120
–140
0
25 50 75 100 125 150 175 200
FREQUENCY (kHz)
1416 F02a
Figure 2a. LTC1416 Nonaveraged, 4096 Point FFT,
Input Frequency = 100kHz
0
fSAMPLE = 400kHz
–20
fIN = 189.9414kHz
SFDR = 94.8dB
SINAD = 80.2dB
–40
–60
–80
–100
–120
–140
0
25 50 75 100 125 150 175 200
FREQUENCY (kHz)
1416 F02b
Figure 2b. LTC1416 Nonaveraged, 4096 Point FFT,
Input Frequency = 190kHz
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 2a shows a typical spectral content with
a 400kHz sampling rate and a 100kHz input. The dynamic
performance is excellent for input frequencies up to and
beyond the Nyquist limit of 200kHz, Figure 2b.
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 = [S/(N + D) – 1.76]/6.02
where ENOB is the Effective Number of Bits of resolution
and S/(N + D) is expressed in dB. At the maximum
sampling rate of 400kHz, the LTC1416 maintains near
ideal ENOBs up to the Nyquist input frequency of 200kHz
(refer to Figure 3).
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NYQUIST
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FREQUENCY
9
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7
6
5
4
3
2
1 fSAMPLE = 400kHz
0
1k
10k
100k
INPUT FREQUENCY (Hz)
86
80
74
68
62
1M 2M
1416 TA02
Figure 3. Effective Bits and Signal/(Noise + Distortion)
vs Input Frequency
8
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