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Optimizing Evaluation Results
3
Optimizing Evaluation Results
This section provides instruction for optimizing the performance during evaluation of the product.
3.1
Clocking Optimization
The sampling clock provided to the ADC needs to have very low noise to achieve optimal results. The
default EVM configuration uses the LMK04828 clocking device to generate the sampling clock. There are
two options to improve the clock noise performance.
1. To achieve the best performance, the LMK04828 can be bypassed in favor of an externally provided
clock that is transformer coupled to the ADC. The clock must have very low noise and must use an
external narrow pass-band filter to achieve optimal noise performance. The clock amplitude must be
within the datasheet limits. See
Section 5.1
for more information regarding this setup.
2. The LMK04828 can be used as a clock distributor by using an external clock as the input to the
LMK04828. Filters should still be used on the clock to optimize the noise performance. See
Section 5.1.2
for more information regarding this setup.
3.2
Coherent Input Source
A Rectangular window function can be applied to the captured data when the sample rate and the input
frequency are set precisely to capture an integer number of cycles of the input frequency (sometimes
called coherent frequency). This may yield better SNR results. The clock and analog inputs must be
frequency locked (such as through 10-MHz references) in order to achieve coherency.
3.3
HSDC Pro Settings
HSDC Pro has some settings that can help improve the performance measurements. These are
highlighted in
Table 4
.
Table 4. HSDC Pro Settings to Optimize Results
HSDC Pro Feature
Description
Analysis Window (samples)
Selects the number of samples to include in the selected test analysis. Collect more data to
improve frequency resolution of FFT analysis. If more than 65,536 samples are required, the
setting in the Data Capture Options will need to be increased to match this value.
Data Windowing Function
Select the desired windowing function applied to the data for FFT analysis. Select
‘Blackman’ when sampling a non-coherent input signal or ‘Rectangle’ when sampling a
coherent input signal.
Test Options
→
Select bins to be removed from the spectrum and back-filled with the average noise level.
Notch Frequency Bins
May also customize which Harmonics/Spurs are considered in SNR and THD calculations
and select the method for calculating spur power.
Test Options
→
Enable markers to narrow the Single-Tone FFT test analysis to a specific bandwidth.
Bandwidth Integration Markers
Data Capture Options
→
Configure the number of contiguous samples per capture (capture depth). May also enable
Capture Options
Continuous Capture and FFT Averaging.
11
SLAU641D – June 2015 – Revised January 2016
ADS5XJ6X Evaluation Module
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