THS4521 Datasheet, PDF (31/43 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4521
THS4522
THS4524
www.ti.com.................................................................................................................................................... SBOS458B – DECEMBER 2008 – REVISED MAY 2009
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 74 was
used to test the performance. 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 75 and Figure 76.
Tabulated ac analysis results are listed in Table 5.
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
1 kW
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 76. 10-kHz FFT
Tone
(Hz)
2k
10 k
Table 5. AC Analysis
Signal
(dBFS)
–0.5
–0.6
SNR
(dBc)
86.7
85.2
THD
(dBc)
–97.8
–98.1
SINAD
(dBc)
86.4
85.2
SFDR
(dBc)
100.7
102.2
Figure 74. THS4521 and ADS8321 Test Circuit
0
-20
-40
-60
-80
-100
-120
-140
-160
0
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 75. 2-kHZ FFT
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