Data acquisition TABLE 3. STANDALONE PGIA KEY SPECIFICATIONS
PGIA Gain (V/V) –3dB Bandwidth (MHz)
2 10 Figure 5. Bandwidth vs. frequency. CMRR
Figure 6 shows the CMRR vs. frequency plot for different PGIA gain settings.
63.54 128.18 47.7 12.99 2.15 0.98 Slew Rate (V/μs) 77 72 10 N/A Drift (μV/°C) 0.06 1.18 0.042 0.026
THD (dB), FIN = 1kHz
–126.5 –116.11 –110.04 –103.32
Figure 6. CMRR vs. frequency.
Distortion The Audio Precision (APX555) signal analyser is used to test the distortion performance of the PGIA board (Figure 4), and its output was set at 8.192Vp-p by applying various input voltage for various gain settings. Figure 7 shows the total harmonic distortion (THD) vs. the frequency performance of the discrete wide bandwidth PGIA.
Figure 8. The simplified signal chain of discrete PGIA driving the ADAQ23875. TABLE 4. DYNAMIC RANGE AND RTI NOISE SUMMARY WHEN THE PGIA DRIVES THE ADAQ23875 PGIA Gain (V/V) 2 10 63.54 128.18 Input Range (Vp-p) 4.096 0.819 0.129 0.064 A PGIA THAT DRIVES SIGNAL Figure 7. A PGIA THD vs. frequency.
Key Specifications Summary A summary of key PGIA specifications such as bandwidth, slew rate, drift, and distortion measured on the bench using the discrete PGIA board (Figure 4) is shown in Table 3.
Instrumentation Monthly November 2022
CHAIN µMODULE SOLUTIONS Figure 8 shows that the selected multiplexer input is followed by the two ADA4898-1 low noise, high speed amplifiers combined with the LT5400 quad precision matched resistor network that drives the ADAQ23875 signal chain μModule at 15MSPS. The ADAQ23875 has an internal fully differential amplifier ; thus, the FDA block of the wide bandwidth discrete PGIA board (Figure 4) should be bypassed. The Audio Precision (APx555) signal source is used for the evaluation of SNR and THD and in this case, the input amplitude was set around –0.5dBFS.
Dynamic Range (dB) RTI Noise (μVrms) 87.68 79.39 78.85 76.83 59.85 31.05 5.20 3.25
Complete Signal Chain Performance Noise
The dynamic range and referred to input (RTI) noise for a specific input range or gain setting of a complete signal chain (Figure 8) are shown in Table 4. The SNR performance vs. frequency of the discrete PGIA driving the ADAQ23875 is shown in Figure 9 when using the ADA4898-1 amplifiers. The overall dynamic range or SNR degradation due to the increase in PGIA gain is attributed to the inherent noise of individual
resistors, amplifiers, and µModule solutions. The precision performance of the
ADAQ23878, combined with a high sampling Continued on page 44...
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