Datasheet

.2 7pF
0.1 Fm
14-bit,
105 MSPS
A
IN+
A
IN–
VBG
ADS
5424
5V
THS4511
CM
348 W
348 W
340 W
340
56.2 W
56.2 W
V
IN
From
50-
source
W
225 W
225 W
49.9 W
49.9 W
0.22 Fm
0.1 Fm
2.7pF
0.1 Fm
A
IN +
A
IN -
CM
ADS5500
5V
THS4511
CM
348 W
348 W
340 W
340 W
56.2 W
56.2 W
49.9 W
V
IN
From
50-
source
W
100 W
14-bit,
125MSPS
100 W
0.22 Fm
0.22 Fm
0.22 Fm
THS4511
SLOS471E –SEPTEMBER 2005–REVISED NOVEMBER 2009 www.ti.com
THS4511 and ADS5500 Combined Performance THS4511 and ADS5424 Combined Performance
The THS4511 is designed to be a high-performance Figure 52 shows the THS4511 driving the ADS5424
drive amplifier for high-performance data converters ADC.
like the ADS5500 14-bit 125-MSPS ADC. Figure 51
As before, the THS4511 amplifier provides 0 dB of
shows a circuit combining the two devices. The
gain, converts the single-ended input to differential,
THS4511 amplifier circuit provides 0 dB of gain, and
and sets the proper input common-mode voltage to
converts the single-ended input signal to a differential
the ADS5424. Input termination and circuit testing is
output signal. The default common-mode output of
the same as described above for the THS4511 and
the THS4511 (2.5 V) is not compatible with the
ADS5500 circuit.
required common-mode input of the ADS5500
(1.55 V), so dc-blocking capacitors are added (0.22
The 225-Ω resistors and 2.7-pF capacitor between
µF). Note that a biasing circuit (not shown in
the THS4511 outputs and ADS5424 inputs (along
Figure 51) is needed to provide the required
with the input capacitance of the ADC) limit the
common-mode, dc-input for the ADS5500. The 100-Ω
bandwidth of the signal to about 100 MHz (–3 dB).
resistors and 2.7-pF capacitor between the THS4511
When the THS4511 is operated from a single power
outputs and ADS5500 inputs along with the input
supply with V
S+
= 5 V and V
S–
= ground, the 2.5-V
capacitance of the ADS5500 limit the bandwidth of
output common-mode voltage is compatible with the
the signal to 115 MHz (–3 dB). For testing, a signal
recommended value of the ADS5424 input
generator is used for the signal source. The
common-mode voltage (2.4 V).
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. See Table 1 for component
values to set proper 50-Ω termination for other
common gains.
Figure 52. THS4511 and ADS5424 Circuit
Figure 51. THS4511 and ADS5500 Circuit
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Product Folder Link(s): THS4511