THS4509 Datasheet, PDF (24/30 Pages) Texas Instruments – WIDEBAND, LOW NOISE, LOW DISTORTION FULLY DIFFERENTIAL AMPLIFIER

THS4509
SLOS454 – JANUARY 2005
Figure 88. THS4509 + ADS5500 2-Tone FFT with
65 MHz and 70 MHz Input
THS4509 + ADS5424 Combined Performance
Figure 89 shows the THS4509 driving the ADS5424
ADC, and Figure 90 shows their combined SNR and
SFDR performance versus frequency with –1 dBFS
input signal level and sampling at 80 MSPS.
As before, the THS4509 amplifier provides 10 dB of
gain, converts the single-ended input to differential,
and sets the proper input common-mode voltage to
the ADS5424. Input termination and circuit testing is
the same as described above for the THS4509 +
ADS5500 circuit.
The 225-Ω resistors and 2.7-pF capacitor between
the THS4509 outputs and ADS5424 inputs (along
with the input capacitance of the ADC) limit the
bandwidth of the signal to about 100MHz (-3dB).
Since the ADS5424s recommended input com-
mon-mode voltage is 2.4 V, the THS4509 is operated
from a single power supply input with V_S+ = 5 V and
V_S– = 0 V (ground).
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From ^VIN
50-W
source
49 .9 W
0.22 mF
100 W
69 .8 W
0.22 mF
100
69 .8 W
0.22 mF
348 W
5V
225 W
THS4509 _{225 W} 2.7 pF
CM
14 -bit,
105 MSPS
A _IN+
ADS 5424
A IN– _VBG
49.9 W
348 W
0.1 mF
0.1 mF
Figure 89. THS4509 + ADS5424 Circuit
95
90
SFDR (dBc)
85
80
SNR (dBFS)
75
70
10
20
30
40
50
60
70
Input Frequency - MHz
Figure 90. THS4509 + ADS5424 SFDR and SNR
Performance vs Frequency
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