Datasheet

www.ti.com
2.1 Signal Conditioning
1 kΩ
1 kΩ
+V
CC
V
I
0.1 µF
1 µF
25 Ω
(+) IN
(−) IN
6800 pF
1 µF
0.1 µF
1 kΩ
−V
CC
−
+
68 pF
1 kΩ
68 pF
V
OCM
25 Ω
−
+
THS4503
+2.048 V
Analog Interface
It is recommended that the analog input to any SAR-type converter be buffered. The amplifier circuit in
Figure 1 is the buffer circuit used on the ADS8402/ADS8406/ADS8412EVM. This circuit consists of the
THS4503, a high-speed fully differential amplifier configured as a single-ended into differential-out, unity
gain buffer. The circuit shown in Figure 1 was optimized to achieve the ac (i.e., SNR, THD, SFDR, etc)
specifications listed in the ADS8402, ADS8406, and ADS8412 data sheets. The 68-pF and 6800-pF
capacitors in the signal path are polypropylene type, manufactured by WIMA Corporation. Polypropylene
capacitors cause the least distortion of the input signal; therefore, they provide good dynamic performance
from the converter. A low-cost alternative for the polypropylene type are C0G capacitors by TDK
Corporation.
Figure 1. Input Buffer Circuit
ADS8402/ADS8406/ADS8412 EVM User's GuideSLAU126A – December 2003 – Revised September 2004 3