Datasheet

LTC1604
16
1604fa
APPLICATIONS INFORMATION
1604 F16
A
IN
+
V
SS
OV
DD
DGNDAV
DD
LTC1604
DIGITAL
SYSTEM
ANALOG
INPUT
CIRCUITRY
AGND
5 TO 8
2
34 29
DV
DD
OGND
2810
1
REFCOMP
4
47μF
V
REF
3
2.2μF
A
IN
–
10μF
36
10μF
AV
DD
35
10μF
10μF
+
–
9
10μF
CODE
–5
–4
–3 –2 –1 0 1 2 3 4 5
COUNT
2500
2000
1500
1000
500
0
1604 F17
FREQUENCY (kHz)
0
AMPLITUDE (dB)
–60
–40
–20
60
1604 F18a
–80
–100
20 40 80 100 120 140 160
–120
–140
0
f
SAMPLE
= 333kHz
f
IN
= 4.959kHz
SINAD = 90.2dB
THD = –103.2dB
Figure 16. Power Supply Grounding Practice
Figure 17. Histogram for 4096 Conversions
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
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
histogram is the transition noise associated with a high
resolution 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 indica-
tion 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 corre-
sponds 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 capability.
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 frequen-
cies outside the fundamental. Figures 18a and 18b show
typical LTC1604 FFT plots.