Datasheet

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2.6 Data Capturing

The board is now ready for a data capture. Before proceeding, perform a manual calibration of

the ADC. Even though the ADC performs a self-calibration at the time of power-up, it is

recommended that the user perform another calibration after sufficient time has passed for the

system (primarily temperature) to stabilize. Manual calibration is performed by clicking the

Calibrate ADC feature in the Register control panel, Settings sub-tab.

2.6.1 Configure Display Settings

Open the FFT Control left panel. Confirm that the dBFS unit is selected. Also confirm that the

correct clock frequency is being measured by the software by checking in the Signal Source

right panel. The default frequency of the on-board clock source is shown in the board

performance data shipped with your board.

2.6.2 Check Input Amplitude

Confirm that the Over-range LEDs are not illuminated. Now increase the signal amplitude until

the LED for the input in use is just barely lit. DO NOT increase signal power much beyond this

point as the ADC's inputs can be damaged if the Operating Maximums are exceeded (see

Electrical Specification section). Then reduce the signal amplitude until the Over-range LED is

no longer illuminated. You should now have an input signal that is very close to the ADC's full-

scale range (e.g., within 0.5 to 1.0 dB).

IMPORTANT: Since the ADC signal and clock inputs are not provided with additional

protection circuitry on this board, the burden is on the user to not overdrive the inputs to

the extent of damaging them. An "Over-range" LED is provided for each channel to

indicate that the signal amplitude is beyond the ADC full-scale range. Keep the signal

amplitude within the operating ratings as specified in the datasheet. Thus, the safe

method of setting the signal amplitude to full-scale level is to utilize the LED as

described in the previous paragraph to roughly obtain the full-scale amplitude and then

inspect the captured data in the software's time-domain plot to fine tune the amplitude to

the desired level.

2.6.3 Acquire and Display Data

Perform a data acquisition by clicking the Acquire Data button (Item #5 in Figure 6).

The acquired data will now appear in the (default) time domain plot window. Switch to the

frequency-domain window (FFT) using the WaveVision 5 controls. Type Ctrl-r to obtain the

summary of the acquisition. Place the software in continuous mode (Item #6 of Figure 6) and

then acquire again. This is to confirm that the Over-range LED method used earlier indeed

gave a signal to the ADC that is within -0.5 to -1.0 dB of the full-scale range. If not, adjust the

input signal generator's signal power to approximately -0.5dB of full scale.

At this point, dynamic performance metrics similar to those shown on the reference data

shipped with the board may be obtained. One of the basic variables that you may experiment

with at this point is to change the input signal strength and frequency. Please note that to

achieve the reference performance, band-pass filters similar to the items referenced in Section

2.2 should be used. The absence of these filters on the input signal or external clock will usually

result in sub-standard performance.

The displayed units should be in dBFS as selected earlier. You may switch the units to dBc and

back to dBFS as desired.