THS4532_15 Datasheet, PDF (40/58 Pages) Texas Instruments – THS4532 Ultra Low Power, Rail-to-Rail Output, Fully-Differential Amplifier

THS4532
SLOS829A – FEBRUARY 2013 – REVISED JULY 2015
9.2.3 SAR ADC Performance: THS5432 and ADS7945 Combined Performance
V_IN±
Differential
Signal from
Generator and
10 kHz BPF
2 k
100 pF
0.22 F
2 k
40.2
5V
+
VOCM
±
V_OUT±
THS4532
V_OUT+
1 nF
ADS7945
2 k
2 k
40.2
V_IN+
100 pF
To Data
Analysis
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Figure 92. THS5432 and ADS7945 Test Circuit
9.2.3.1 Design Requirements
To show achievable performance with a high performance SAR ADC, the THS5432 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 92 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 93. A summary of the FFT analysis results are in Table 8 along with
ADS7945 typical data sheet performance at f_S = 2 MSPS. Refer to the data sheet for more information.
9.2.3.2 Detailed Design Procedure
The standard ADS7945 EVM and THS5432 EVM are modified to implement the schematic in Figure 92 and used
to test the performance of the THS5432 as a drive amplifier. With single supply 5 V supply the output common-
mode of the THS5432 defaults to +2.5 V as required at the input of the ADS7945 so the V_OCM input of the
THS5432 simply bypassed to GND with 0.22-µF capacitor. The summary of results of the FFT analysis versus
typical data sheet performance shown in Table 8 show that the THS5432 will make an excellent drive amplifier
for this ADC.
9.2.3.3 Application Curve
0
−10
−20
−30
−40
−50
−60
−70
−80
−90
−100
−110
−120
−130
−140
1k
V_S = 5 V
G = 1 V/V
R_F = 2 kΩ
V_OUT = −0.5 dBFS
10k
100k
Frequency (Hz)
1M
G077
Figure 93. THS5432 and ADS7945 Test Circuit
CONFIGURATION
THS5432 + ADS7945
ADS7945 Data Sheet (typ)
Table 8. 10-kHz FFT Analysis Summary
TONE
10 kHz
10 kHz
SIGNAL
–0.5 dBFS
–0.5 dBFS
SNR
83 dBc
84 dBc
THD
–93 dBc
–92 dBc
SFDR
96 dBc
94 dBc
40
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