www.ti.com
45
50
55
60
65
70
75
80
85
90
95
100
f − Frequency − MHz
SFDR − Spurious−Free Dynamic Range − dBc
G001
9.97
30.13
50.13
69.59
89.75
130.13
230.53
301.13
401.13
501.13
Mini Circuits
TC4−1W
Mini Circuits
TC1−1T
Coilcraft
WBC1−1TLB
45
50
55
60
65
70
75
80
85
90
95
100
f − Frequency − MHz
SFDR − Spurious−Free Dynamic Range − dBc
G002
9.97
30.13
50.13
69.59
89.75
130.13
230.53
301.13
401.13
501.13
Mini Circuits
TC4−1W
Mini Circuits
TC1−1T
Coilcraft
WBC1−1TLB
Circuit Description
For an ac-coupled system, users should use the voltage divider R9 and R18 to set the common-mode
input of the amplifier, which should be set to the midpoint of the amplifier supply. C46 and C47 ac-couple
the system, and the ADC inputs can then be biased by the R14 and R15 combination. Another ac-coupled
approach, not supported on this EVM, would be to use a transformer at the outputs of the THS4509. In
this case, the transformer would provide for ac-coupling, and one could bias the inputs of the ADC by
feeding the ADC VCM to the transformer center tap on the secondary.
It should be noted that the THS4509 used on this EVM is pinout-compatible with the THS4508, THS4511,
THS4513, and THS4520. Users can easily interchange the amplifier on this EVM and should pick the
appropriate amplifier based on commmon mode range, power supplies, and frequency of operation. TI
application engineers can assist in the best selection of these amplifiers based on the user requirements.
SFDR vs Frequency Using a Single Transformer
Figure 1.
SFDR vs Frequency Using a Dual Transformer
Figure 2.
8
SLAU196 – April 2007
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