THS4513 Datasheet, PDF (28/34 Pages) Texas Instruments – WIDEBAND, LOW NOISE, LOW DISTORTION FULLY DIFFERENTIAL AMPLIFIER

THS4513
SLOS472 – AUGUST 2005
inserted to ground across the 69.8-Ω resistor and
0.22-µF capacitor on the alternate input to balance
the circuit. Gain is a function of the source im-
pedance, termination, and 348-Ω feedback resistor.
Refer to Table 3 for component values to set proper
50-Ω termination for other common gains. A split
power supply of +4V and -1V is used to set the input
and output common-mode voltages to approximately
mid-supply while setting the input common-mode of
the ADS5500 to the recommended +1.55V. This
maintains maximum headroom on the internal transis-
tors of the THS4513 to insure optimum performance.
From ^VIN
50-W
source
49.9 W
0.22 mF
340 W
348 W
56.2 W
4V
0.22 mF
340 W
THS 4513
56.2 W
0.22 mF
CM
-1 V
348 W
100 W
100 W^{2.7 pF}
0.1 mF
14 -bit,
125 MSPS
A IN +
ADS5500
A IN - _CM
49.9 W
0.1 mF
Figure 84. THS4513 + ADS5500 Circuit
Figure 85 shows the 2-tone FFT of the THS4513 +
ADS5500 circuit with 65 MHz and 70 MHz input
frequencies. The SFDR is 90 dBc.
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Figure 85. THS4513 + ADS5500 2-Tone FFT with
65 MHz and 70 MHz Input
THS4513 + ADS5424 Combined Performance
Figure 86 shows the THS4513 driving the ADS5424
ADC.
As before, the THS4513 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 THS4513 +
ADS5500 circuit.
The 225-Ω resistors and 2.7-pF capacitor between
the THS4513 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 THS4513 is operated
from a single power supply input with V_S+ = 5 V and
V_S– = 0 V (ground).
From ^VIN
50-W
source
49 .9 W
340 W
56.2 W
0.22 mF
340
56.2 W
348 W
5V
225 W
THS4513 _{225 W} 2.7 pF
CM
14 -bit,
105 MSPS
A _IN+
ADS 5424
A IN– _VBG
49.9 W
0.22 mF
0.22 mF
348 W
0.1 mF
0.1 mF
Figure 86. THS4513 + ADS5424 Circuit
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