THS4509-Q1 Datasheet, PDF (29/37 Pages) Texas Instruments – WIDEBAND LOW-NOISE LOW-DISTORTION FULLY DIFFERENTIAL AMPLIFIER

THS4509-Q1
www.ti.com........................................................................................................................................................................................... SLOS547 – NOVEMBER 2008
Figure 89 shows the two-tone FFT of the THS4509 +
ADS5500 circuit with 65-MHz and 70-MHz input
frequencies. The SFDR is 90 dBc.
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
THS4509
225 W
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 90. THS4509 + ADS5424 Circuit
95
90
SFDR (dBc)
Figure 89. THS4509 + ADS5500 Two-Tone FFT
with 65-MHz and 70-MHz Input
THS4509 + ADS5424 Combined Performance
Figure 90 shows the THS4509 driving the ADS5424
ADC, and Figure 91 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 previously described 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 100 MHz (–3 dB).
Since the ADS5424's recommended input
common-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).
85
80
SNR (dBFS)
75
70
10
20
30
40
50
60
70
Input Frequency - MHz
Figure 91. THS4509 + ADS5424 SFDR and
SNR Performance vs Frequency
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): THS4509-Q1
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