Datasheet

.2 7pF
0.1 Fm
14-bit,
105 MSPS
A
IN+
A
IN–
VBG
ADS
5424
5V
THS4508
CM
348 W
348 W
100 W
100
69.8 W
V
IN
From
50-
source
W
225 W
225 W
69.8 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
THS4508
CM
348 W
348 W
100 W
100 W
69.8 W
69.8 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
70
65
75
80
85
90
95
10 20 30 40 50 60
InputFrequency-MHz
SFDR
SNR
60
65
70
75
80
85
90
95
10 20 30 40 50 60 70 80 90 100 110
InputFrequency-MHz
SFDR
SNR
THS4508 + ADS5424 Combined Performance
THS4508
SLAS459E – SEPTEMBER 2005 – REVISED SEPTEMBER 2008 .................................................................................................................................... www.ti.com
source. Input termination is accomplished via the The 225- Ω resistors and 2.7-pF capacitor between
69.8- Ω resistor and 0.22- µ F capacitor to ground in the THS4508 outputs and ADS5424 inputs (along
conjunction with the input impedance of the amplifier with the input capacitance of the ADC) limit the
circuit. A 0.22- µ F capacitor and 49.9- Ω resistor is bandwidth of the signal to about 100 MHz ( – 3 dB).
inserted to ground across the 69.8- Ω resistor and
When the THS4508 is operated from a single power
0.22- µ F capacitor on the alternate input to balance
supply with V
S+
= 5 V and V
S –
= ground, the 2.5-V
the circuit. Gain is a function of the source
output common-mode voltage is compatible with the
impedance, termination, and 348- Ω feedback resistor.
recommended value of the ADS5424 input
See Table 1 for component values to set proper 50- Ω
common-mode voltage (2.4 V).
termination for other common gains.
Figure 59. THS4508 + ADS5424 Circuit
Figure 57. THS4508 + ADS5500 Circuit
Figure 60. THS4508 + ADS5424 SFDR and SNR
Figure 58. THS4508 + ADS5500 SFDR and SNR
Performance vs Frequency
Performance versus Frequency
Figure 59 shows the THS4508 driving the ADS5424
ADC, and Figure 60 shows the combined SNR and
SFDR performance versus frequency with – 1 dBFS
input signal level and sampling at 80 MSPS.
As before, the THS4508 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 THS4508 +
ADS5500 circuit.
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Product Folder Link(s): THS4508