Datasheet
−140
−130
−120
−110
−100
−90
−80
−70
−60
−50
−40
−30
−20
−10
0
0 10k 20k 30k 40k 50k
Frequency (Hz)
Magnitude (dBFS)
V
S
= 5 V
G = 1 V/V
R
F
= 2 kΩ
V
OUT
= −0.5 dBFS
G078
2 k
2 k
0.22 F
5V
THS4531A
V
OUT+
121
V
OUT±
121
Single-Ended
Signal from
Generator and
10 kHz BPF
V
IN+
V
IN±
+
±
V
OCM
2 k
2.2 nF
2 k
To Data
Analysis
ADS8321
100 pF
100 pF
220 pF
220 pF
No Input
49.9
49.9
THS4531A
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SLOS823A –DECEMBER 2012–REVISED JANUARY 2013
The standard ADS8321 EVM and THS4531A EVM are modified to implement the schematic in Figure 91 and
used to test the performance of the THS4531A as a drive amplifier. With single supply +5V supply the output
common-mode of the THS4531A defaults to +2.5V as required at the input of the ADS8321 so the V
OCM
input of
the THS4531A 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 THS4531A will make an excellent drive
amplifier for this ADC.
Figure 91. THS4531A and ADS8321 Test Circuit
Figure 92. THS4531A + ADS8321 1kHz FFT
Table 5. 10kHz FFT Analysis Summary
CONFIGURATION TONE SIGNAL SNR THD SINAD SFDR
THS4531A + ADS8321 10kHz -0.5 dBFS 87 dBc -96 dBc 87 dBc 100 dBc
ADS8321 Data Sheet (typ) 10kHz -0.5 dBFS 87 dBc -86 dBc 84 dBc 86 dBc
THS4531A and ADS7945 Combined Performance
To show achievable performance with a high performance SAR ADC, the THS4531A 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 93 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 94. A summary of the FFT analysis results are in Table 6 along with
ADS7945 typical data sheet performance at f
S
= 2MSPS. Please refer to its data sheet for more information.
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