THS4513_14 Datasheet, PDF (28/42 Pages) Texas Instruments – WIDEBAND, LOW-NOISE, LOW-DISTORTION FULLY-DIFFERENTIAL AMPLIFIER

THS4513
SLOS472E – AUGUST 2005 – REVISED JANUARY 2013
THS4513 and ADS5500 Combined Performance
The THS4513 is designed to be a high-performance
drive amplifier for high-performance data converters
like the ADS5500 14-bit 125-MSPS ADC. Figure 84
shows a circuit combining the two devices. The
THS4513 amplifier circuit provides 10 dB of gain,
converts the single-ended input to differential, and
sets the proper input common-mode voltage to the
ADS5500. The 100-Ω resistors and 2.7-pF capacitor
between the THS4513 outputs and ADS5500 inputs
along with the input capacitance of the ADS5500 limit
the bandwidth of the signal to 115 MHz (–3 dB). For
testing, a signal generator is used for the signal
source. The generator is an ac-coupled 50-Ω source.
A band-pass filter is inserted in series with the input
to reduce harmonics and noise from the signal
source. Input termination is accomplished via the
69.8-Ω resistor and 0.22-μF capacitor to ground in
conjunction with the input impedance of the amplifier
circuit. A 0.22-μF capacitor and 49.9-Ω resistor is
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
impedance, 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 +4 V and –1 V is used to set the
input and output common-mode voltages to
approximately midsupply while setting the input
common-mode of the ADS5500 to the recommended
+1.55 V. This configuration maintains maximum
headroom on the internal transistors of the THS4513
to ensure 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 and ADS5500 Circuit
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Figure 85 shows the two-tone FFT of the THS4513
and ADS5500 circuit with 65 MHz and 70 MHz input
frequencies. The SFDR is 90 dBc.
Figure 85. THS4513 and ADS5500 2-Tone FFT
with 65-MHz and 70-MHz Inputs
THS4513 and 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 and
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 100 MHz (–3 dB).
Since the ADS5424 recommended input common-
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
0.22 mF
340 W
56.2 W
0.22 mF
340
56.2 W
0.22 mF
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
348 W
0.1 mF
0.1 mF
Figure 86. THS4513 and ADS5424 Circuit
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