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
ADS614x
THS4509
VCM
500 W
200 W
200 W
5 W
5 W
500 W
0.1 Fm
–V
S
ADS6145, ADS6144
ADS6143, ADS6142
SLWS198B – JULY 2007 – REVISED MARCH 2008
Figure 97. Two Transformer Drive Circuit
Figure 98 shows a drive circuit using a differential amplifier (TI's THS4509) to convert a single-ended input to a
differential output that can be interfaced to the ADC analog input pins. In addition to the single-ended to
differential conversion, the amplifier also provides gain (10 dB in Figure 98 ). 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 98. Drive Circuit Using the THS4509
See the EVM User Guide (SLWU028 ) for more information.
44 Submit Documentation Feedback Copyright © 2007 – 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS6145, ADS6144 ADS6143, ADS6142