ADS5547 Datasheet, PDF (30/50 Pages) Texas Instruments – 14-BIT, 210 MSPS ADC WITH DDR LVDS/CMOS OUTPUTS

ADS5547
SLWS192 – NOVEMBER 2006
www.ti.com
APPLICATION INFORMATION (continued)
In addition to the above ADC requirements, the drive circuit may have to be designed to provide a low insertion
loss over the desired frequency range and matched impedance to the source. For this, the ADC input
impedance has to be taken into account (Figure 40).
Example Drive Circuits
A suitable configuration using RF transformers and including the R-C-R filter is shown in Figure 38. Note the
15-Ω series resistors and the low common-mode impedance (using 33-Ω resistors terminated to VCM).
0.1 mF ^WBC1-1TLB
1:1
WBC1-1TLB
100 W
100 W
1:1
Z_i and TFADC
15 W
(Note A)
0.1 mF
33 W
33 W
25 W
3.3 pF
25 W
15 W
(Note A)
ADS5547
INP
INM
VCM
A. Use lower series resistance (≈ 5 Ω to 10 Ω) at high input frequencies (> 100 MHz)
Figure 38. Example Drive Circuit With RF Transformers
2
1
0
-1
-2
-3
-4
-5
-6
0
100 200 300 400 500 600 700 800 900 1000
f − Frequency − MHz
Figure 39. Analog Input Bandwidth, TFADC (Actual Silicon Data)
30
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