THS4531A Datasheet, PDF (37/50 Pages) Texas Instruments – Ultra Low Power, Rail-to-Rail Output, Fully-Differential Amplifier

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THS4531A
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.
No Input V_IN±
Single-Ended
Signal from
Generator and
V_IN+
10 kHz BPF
2k
100 pF
49.9
0.22 F
2k
100 pF
49.9
2k
121
5V
+
V_OCM
±
V_OUT±
THS4531A
V_OUT+
2k
121
220 pF
2.2 nF
ADS8321
To Data
Analysis
220 pF
Figure 91. THS4531A and ADS8321 Test Circuit
0
−10
−20
−30
−40
−50
−60
−70
−80
−90
−100
−110
−120
−130
−140
0
V_S = 5 V
G = 1 V/V
R_F = 2 kΩ
V_OUT = −0.5 dBFS
10k
20k
30k
40k
50k
Frequency (Hz)
G078
Figure 92. THS4531A + ADS8321 1kHz FFT
CONFIGURATION
THS4531A + ADS8321
ADS8321 Data Sheet (typ)
Table 5. 10kHz FFT Analysis Summary
TONE
10kHz
10kHz
SIGNAL
-0.5 dBFS
-0.5 dBFS
SNR
87 dBc
87 dBc
THD
-96 dBc
-86 dBc
SINAD
87 dBc
84 dBc
SFDR
100 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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