Datasheet

10W Wto15
10W Wto15
0.1 Fm
0.1 Fm
T2
1:1
T1
1:1
25W
25W
50W
3.3pF
50W
INP
INM
VCM
C
IN
R
IN
ADS41xx
3.6nH
3.6nH
5 to10W W
5 to10W W
0.1 Fm
0.1 Fm
T2
1:1
T1
1:1
25W
25W
INP
INM
VCM
C
IN
R
IN
ADS41xx
ADS4122, ADS4125
ADS4142, ADS4145
SBAS520A –FEBRUARY 2011– REVISED MARCH 2011 www.ti.com
Driving Circuit
Two example driving circuit configurations are shown in Figure 104 and Figure 105—one optimized for low
bandwidth (tlow input frequencies) and the other one for high bandwidth to support higher input frequencies. In
Figure 104, an external R-C-R filter with 3.3pF is used to help absorb sampling glitches. The R-C-R filter limits
the bandwidth of the drive circuit, making it suitable for low input frequencies (up to 250MHz). Transformers such
as ADT1-1WT or WBC1-1 can be used up to 250MHz.
For higher input frequencies, the R-C-R filter can be dropped. Together with the lower series resistors (5Ω to
10Ω), this drive circuit provides higher bandwidth to support frequencies up to 500MHz (as shown in Figure 105).
A transmission line transformer such as ADTL2-18 can be used.
Note that both the drive circuits have been terminated by 50Ω near the ADC side. The termination is
accomplished by a 25Ω resistor from each input to the 0.95V common-mode (VCM) from the device. This
termination allows the analog inputs to be biased around the required common-mode voltage.
Figure 104. Drive Circuit with Low Bandwidth (for Low Input Frequencies)
Figure 105. Drive Circuit with High Bandwidth (for High Input Frequencies)
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Product Folder Link(s): ADS4122 ADS4125 ADS4142 ADS4145