Datasheet

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INP
INM
VCM
1 :1
5 W
0 .1
mF
1 :1
50 W
50 W
0 .1
mF
50 W
50 W
5 W
Using Differential Amplifier Drive Circuits
R
G
R
F
R
F
R
FIL
R
FIL
C
FIL
C
FIL
R
G
0.1 Fm
0.1 Fm
0.1 Fm
0.1 Fm
0.1 Fm
0.1 Fm
0.1 Fm
10 Fm
10 Fm
R
S
R
S T
||R
R
T
+V
S
CM
INP
INM
ADS612x
THS4509
VCM
500 W
200 W
200 W
5 W
5 W
500 W
0.1 Fm
–V
S
ADS6125, ADS6124
ADS6123, ADS6122
SLAS560A – OCTOBER 2007 – REVISED MARCH 2008
Figure 94. Two Transformer Drive Circuit
Figure 95 shows a drive circuit using a differential amplifier (TI's THS4509) to convert a single-ended input to
differential output that can be interface to the ADC analog input pins. In addition to the single-ended to differential
conversion, the amplifier also provides gain (10 dB in Figure 95 ). R
FIL
helps to isolate the amplifier outputs from
the switching input of the ADC. Together with C
FIL
it also forms a low-pass filter that band-limits the noise (and
signal) at the ADC input. As the amplifier output is ac-coupled, the common-mode voltage of the ADC input pins
is set using two 200 Ω resistors connected to VCM.
The amplifier output can also be dc-coupled. Using the output common-mode control of the THS4509, the ADC
input pins can be biased to 1.5 V. In this case, use +4 V and -1 V supplies for the THS4509 so that its output
common-mode voltage (1.5 V) is at mid-supply.
Figure 95. Drive Circuit Using the THS4509
See the EVM User Guide (SLWU028 ) for more information.
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Product Folder Link(s): ADS6125, ADS6124 ADS6123, ADS6122