LTC1604CG View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1604CG' PDF : 20 Pages View PDF
LTC1604
APPLICATIONS INFORMATION
ANALOG
INPUT
CIRCUITRY
1 AIN+
AIN– VREF REFCOMP AGND
LTC1604
VSS AVDD AVDD DVDD DGND
+– 2
3
4
5 TO 8 34 36 35
9
10
2.2µF 47µF
10µF 10µF 10µF 10µF
OVDD OGND
29 28
10µF
DIGITAL
SYSTEM
1604 F16
Figure 16. Power Supply Grounding Practice
DC PERFORMANCE
The noise of an ADC can be evaluated in two ways: signal-
to-noise raio (SNR) in frequency domain and histogram in
time domain. The LTC1604 excels in both. Figure 18a
demonstrates that the LTC1604 has an SNR of over 90dB
in frequency domain. The noise in the time domain histo-
gram is the transition noise associated with a high resolu-
tion ADC which can be measured with a fixed DC signal
applied to the input of the ADC. The resulting output codes
are collected over a large number of conversions. The
shape of the distribution of codes will give an indication of
the magnitude of the transition noise. In Figure 17 the
distribution of output codes is shown for a DC input that
has been digitized 4096 times. The distribution is Gaussian
and the RMS code transition noise is about 0.66LSB. This
corresponds to a noise level of 90.9dB relative to full scale.
Adding to that the theoretical 98dB of quantization error
for 16-bit ADC, the resultant corresponds to an SNR level
of 90.1dB which correlates very well to the frequency
domain measurements in DYNAMIC PERFORMANCE
section.
DYNAMIC PERFORMANCE
The LTC1604 has excellent high speed sampling capabil-
ity. Fast fourier transform (FFT) test techniques are used
to test the ADC’s frequency response, distortions and
noise at the rated throughput. By applying a low distortion
sine wave and analyzing the digital output using an FFT
algorithm, the ADC’s spectral content can be examined for
frequencies outside the fundamental. Figures 18a and 18b
show typical LTC1604 FFT plots.
2500
2000
1500
1000
500
0
–5 –4 –3 –2 –1 0 1 2 3 4 5
CODE
1604 F17
Figure 17. Histogram for 4096 Conversions
0
fSAMPLE = 333kHz
–20
fIN = 4.959kHz
SINAD = 90.2dB
THD = –103.2dB
–40
–60
–80
–100
–120
–140
0 20 40 60 80 100 120 140 160
FREQUENCY (kHz)
1604 F18a
Figure 18a. This FFT of the LTC1604’s Conversion of a
Full-Scale 5kHz Sine Wave Shows Outstanding Response
with a Very Low Noise Floor When Sampling at 333ksps
16
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