THS4521_10 Datasheet, PDF (35/48 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

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ADC Driver Performance:
THS4521 and ADS8321 Combined
Performance
To demonstrate achievable performance, the
THS4521 is tested as the drive amplifier for the
ADS8321 16-bit SAR ADC. The ADS8321 offers
excellent ac and dc performance, with ultra-low power
and small size. The circuit shown in Figure 84 was
used to test the performance.
THS4521
THS4522
THS4524
SBOS458D – DECEMBER 2008 – REVISED AUGUST 2010
Data were taken using the ADS8321 at 100 kSPS
with input frequencies of 2 kHz and 10 kHz and
signal levels that were -0.5 dBFS. FFT plots that
illustrate the spectral performance are given in
Figure 85 and Figure 86. Tabulated ac analysis
results are listed in Table 7 and compared to the
ADS8321 data sheet typical performance.
V_IN+
V_IN-
1 kW
1 kW
1 kW
5V
THS4521
V_OCM
49.9 W
49.9 W
Open
0.22 mF
68 pF
1 nF
68 pF
-IN
ADS8321
+IN
0
-20
-40
-60
-80
-100
-120
-140
-160
0
1 kW
Figure 84. THS4521 and ADS8321 Test Circuit
2-kHz FFT
V_S = 5.0 V
G = 1 V/V
R_F = R_G = 1 kW
Load = 2 x 49.9 W + 2 pF
10 k
20 k
30 k
40 k
50 k
Frequency (Hz)
Figure 85. 2-kHZ FFT
0
-20
-40
-60
-80
-100
-120
-140
-160
0
10-kHz FFT
V_S = 5.0 V
G = 1 V/V
R_F = R_G = 1 kW
Load = 2 x 49.9 W + 2 pF
10 k
20 k
30 k
40 k
50 k
Frequency (Hz)
Figure 86. 10-kHz FFT
Configuration
THS4521 and
ADS8321
ADS8321 Data
sheet (typ)
Tone
2 kHz
10 kHz
10 kHz
Table 7. AC Analysis
Signal (dBFS)
–0.5
–0.5
SNR (dBc)
86.7
85.2
THD (dBc)
–97.8
–98.1
–0.5
87
–86
SINAD (dBc)
86.4
85.2
84
SFDR (dBc)
100.7
102.2
86
Copyright © 2008–2010, Texas Instruments Incorporated
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