ADS802 Datasheet, PDF (13/17 Pages) Burr-Brown (TI) – 12-Bit, 10MHz Sampling ANALOG-TO-DIGITAL CONVERTER

+5V
+5V
10kΩ
REF1004
+2.5V
A₁
1/2
OPA2234
2kΩ
6.2kΩ
0.1µF
10kΩ⁽¹⁾
10kΩ
10kΩ⁽¹⁾
10kΩ
A₂
1/2
OPA2234
R_P
220Ω
Top
Reference
+2.5V to +3.25V
+1.25V
R_P
220Ω
Bottom
Reference
NOTE: (1) Use parts alternatively for adjustment capability.
FIGURE 8. Optional External Reference to Set the Full-Scale Range Utilizing a Dual, Single-Supply Op Amp.
ground planes can give excellent results. It is recommended
that the analog and digital ground pins of the ADS802 be
connected directly to the analog ground plane. In our experi-
ence, this gives the most consistent results. The A/D converter
power-supply commons should be tied together at the analog
ground plane. Power supplies should be bypassed with 0.1µF
ceramic capacitors as close to the pin as possible.
DYNAMIC PERFORMANCE TESTING
The ADS802 is a high-performance converter and careful
attention to test techniques is necessary to achieve accurate
results. Highly accurate phase-locked signal sources allow
high resolution FFT measurements to be made without using
data windowing functions. A low-jitter signal generator, such
as the HP8644A for the test signal, phase-locked with a low-
jitter HP8022A pulse generator for the A/D converter clock,
gives excellent results. Low-pass filtering (or bandpass filter-
ing) of test signals is absolutely necessary to test the low
distortion of the ADS802. Using a signal amplitude slightly
lower than full-scale will allow a small amount of “headroom”
so that noise or DC-offset voltage will not overrange the A/D
converter and cause clipping on signal peaks.
DYNAMIC PERFORMANCE DEFINITIONS
1.
Signal-to-Noise-and-Distortion Ratio (SINAD):
10 log
Noise
Sinewave Signal Power
+ Harmonic Power (first 15 harmonics)
2.
Signal-to-Noise Ratio (SNR):
10 log ^{Sinewave Signal Power}
Noise Power
3.
Intermodulation Distortion (IMD):
10 log ^{Highest IMD Pr oduct Power (to 5th − order)}
Sinewave Signal Power
IMD is referenced to the larger of the test signals f₁ or f₂. Five
“bins” either side of peak are used for calculation of funda-
mental and harmonic power. The “0” frequency bin (DC) is
not included in these calculations, as it is of little importance
in dynamic signal processing applications.
ADS802
13
SBAS039B
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