THS4531
SLOS358B –SEPTEMBER 2011–REVISED MARCH 2012
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The standard ADS8321 EVM and THS4531 EVM are modified to implement the schematic in Figure 89 and used
to test the performance of the THS4531 as a drive amplifier. With single supply +5V supply the output common-
mode of the THS4531 defaults to +2.5V as required at the input of the ADS8321 so the VOCM input of the
THS4531 simply bypassed to GND with 0.22µF capacitor. The summary of results of the FFT analysis versus
typical data sheet performance shown in Table 5 show the THS4531 will make an excellent drive amplifier for
this ADC.
2 kȍ
2 kȍ
121 ȍ
No Input
VIN–
100 pF
220 pF
2.2 nF
5V
49.9 ȍ
VOUT–
To Data
Analysis
+
VOCM
THS4531
VOUT+
ADS8321
–
0.22 ȝF
2 kȍ
Single-Ended
Signal from
2 kȍ
121 ȍ
VIN+
Generator and
10 kHz BPF
100 pF
220 pF
49.9 ȍ
Figure 89. THS4531 and ADS8321 Test Circuit
0
−10
−20
−30
−40
VS = 5 V
G = 1 V/V
RF = 2 kΩ
VOUT = −0.5 dBFS
−50
−60
−70
−80
−90
−100
−110
−120
−130
−140
0
10k
20k
30k
40k
50k
Frequency (Hz)
G078
Figure 90. THS4531 + ADS8321 1kHz FFT
Table 5. 10kHz FFT Analysis Summary
CONFIGURATION
THS4531 + ADS8321
TONE
10kHz
10kHz
SIGNAL
-0.5 dBFS
-0.5 dBFS
SNR
THD
SINAD
SFDR
100 dBc
86 dBc
87 dBc
87 dBc
-96 dBc
-86 dBc
87 dBc
84 dBc
ADS8321 Data Sheet (typ)
THS4531 and ADS7945 Combined Performance
To show achievable performance with a high performance SAR ADC, the THS4531 is tested as the drive
amplifier for the ADS7945. The ADS7945 is a 14-bit, SAR ADC that offers excellent AC and DC performance,
with low power and small size. The circuit shown in Figure 91 is used to test the performance. Data was taken
using the ADS7945 at 2MSPS with input frequency of 10 kHz and signal level 0.5 dB below full scale. The FFT
plot of the spectral performance is in Figure 92. A summary of the FFT analysis results are in Table 6 along with
ADS7945 typical data sheet performance at fS = 2MSPS. Please refer to its data sheet for more information.
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