Spectral Analysis Tool - Texas Instruments ADS8900BEVM-PDK User Manual

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6.4

Spectral Analysis Tool

The spectral analysis tool is intended to evaluate the dynamic performance (SNR, THD, SFDR, SINAD,
and ENOB) of the ADS8900B SAR ADC through single-tone sinusoidal signal FFT analysis using the 7-
term Blackman-Harris window setting. Also, the window setting of None can be used to search for noise
spurs over frequency in dc inputs.
For dynamic performance evaluation, the external differential source must have better specifications than
the ADC itself to ensure that the measured system performance is not limited by the performance of the
signal source. Therefore, the external reference source must meet the source requirements mentioned in
Table 4.
Table 4. External Source Requirements for Evaluation of the ADS8900B
Specification Description
External source common-mode
External source impedance (R
External source differential impedance
Source differential signal
(V
PP
For 2-kHz SNR and ENOB evaluation at a maximum throughput of 1 MSPS, the number of samples must
be 32768 or 65536. More samples brings the noise floor so low that the external source phase noise can
dominate the SNR and ENOB calculations. On the contrary, for THD and SFDR evaluation, a much larger
number of samples must be used to reduce the noise floor below –140 dBc to analyze noise-free
harmonics and spurs in the order of –120 dBc. Such analysis requires at least 262144 samples.
SBAU269 – October 2016
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Signal frequency
External source type
)
S
(R = 2 × R )
S_DIFF S
Amplitude for –0.1 dBFS)
Maximum noise
Maximum SNR
Maximum THD
Copyright © 2016, Texas Instruments Incorporated
ADS8900BEVM-PDK Operation
Specification Value
2 kHz
Balanced differential
0 V or floating
(see Section 2.2.2 for jumper settings)
10 Ω–30 Ω
20 Ω–60 Ω
–3
(2 × R × 4.45 × 10 ) + 8.9 V
S
or
–3
(R × 4.45 × 10 ) + 8.9 V
S_DIFF
10 µV
RMS
110 dB
–130 dB
ADS8900BEVM-PDK
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