CN0385 Datasheet, PDF (8/13 Pages) Analog Devices – Devices Connected

CN-0385
Table 5 shows the gain error measured for each of the gain
configurations for the circuit in Figure 1. The %FS error was
found using the analysis methods described previously, and the
actual gain in V/V was calculated by subtracting this error from
the ideal gain.
Table 5. Gain Error Measurements for all Gain Configurations
Gain
Gain Error (%FS)
0.4
0.02
0.8
0.02
1.6
0.03
3.2
0.02
Performance Results Without Channel Switching
Figure 10, Figure 11, Figure 12, and Figure 13 show the fast
Fourier transform (FFT) plots for a 10 kHz, full-scale, sine wave
input on a single channel for gain configurations of 0.4, 0.8, 1.6,
and 3.2, respectively. Table 6 shows the SNR and rms noise
measured for each of the gain configurations.
Table 6. SNR, Noise, and THD vs. Gain for 10 kHz Input
Gain
SNR (dB) RMS Noise (µV rms) THD (dB)
0.4
93.9
55.2
−99.2
0.8
92.8
62.6
−98.5
1.6
90.6
80.7
−97.0
3.2
88.0
108.9
−94.6
The input signal was supplied by an Audio Precision SYS-2700
series signal generator, with the board set in differential input
mode. Figure 14 shows total harmonic distortion (THD)
measurements vs. the frequency of the input signal for each
gain configuration.
0
f_S = 1.5MSPS
–20
f_IN = 10kHz
SNR = 92.52dB
–40
THD = –93.96dB
–60
–80
–100
–120
–140
–160
–180
–200
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
FREQUENCY (kHz)
Figure 10. FFT for 10 kHz, 20 V p-p Input for Gain = 0.4 on Single,
Static Channel
Circuit Note
0
f_S = 1.5MSPS
–20
f_IN = 10kHz
SNR = 91.48dB
–40
THD = –94.35dB
SINAD = 89.67dB
–60
–80
–100
–120
–140
–160
–180
–200
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
FREQUENCY (kHz)
Figure 11. FFT for 10 kHz, 10 V p-p Input for Gain = 0.8 on Single,
Static Channel
0
f_S = 1.5MSPS
–20
f_IN = 10kHz
SNR = 90.25dB
–40
THD = –94.12dB
SINAD = 88.76dB
–60
–80
–100
–120
–140
–160
–180
–200
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
FREQUENCY (kHz)
Figure 12. FFT for 10 kHz, 5 V p-p Input for Gain = 1.6 on Single,
Static Channel
0
f_S = 1.5MSPS
–20
f_IN = 10kHz
SNR = 87.77dB
–40
THD = –93.27dB
SINAD = 86.69dB
–60
–80
–100
–120
–140
–160
–180
–200
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
FREQUENCY (kHz)
Figure 13. FFT for 10 kHz, 2.5 V p-p Input for Gain = 3.2 on Single,
Static Channel
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