ADS62P25 Datasheet, PDF (43/71 Pages) Texas Instruments – DUAL CHANNEL, 12-BITS, 125/105/80/65 MSPS ADC WITH DDR LVDS/CMOS OUTPUTS

www.ti.com
ADS62P25, ADS62P24
ADS62P23, ADS62P22
SLAS576A – OCTOBER 2007 – REVISED FEBRUARY 2008
0.1 mF
50 W
0.1 mF
50 W
ADS62P2x
INP
50 W
50 W
INM
1:1
1:1
VCM
Figure 85. Drive Circuit at High Input Frequencies
S0164-07
Using Differential Amplifier Drive Circuits
Figure 86 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). 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.
R_F
+V_S
R_S
0.1 mF _RG
500 W
0.1 mF 10 mF
0.1 mF
R_T
CM THS4509
R_G
R_S || R_T
0.1 mF
500 W
–V_S
0.1 mF 10 mF
R_FIL
0.1 mF
5W
C_FIL
200 W
ADS62P2x
INP
R_FIL
C_FIL
0.1 mF
200 W
5W
0.1 mF
INM
VCM
R_F
Figure 86. Drive Circuit Using the THS4509
S0259-04
Copyright © 2007–2008, Texas Instruments Incorporated
Submit Documentation Feedback
43
Product Folder Link(s): ADS62P25, ADS62P24 ADS62P23, ADS62P22