THS1007_14 Datasheet, PDF (29/34 Pages) Texas Instruments – 10-BIT, 4 ANALOG INPUT, 6-MSPS, SIMULTANEOUS SAMPLING ANALOG-TO-DIGITAL CONVERTER

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THS1007
SLAS286B − AUGUST 2000− REVISED DECEMBER 2010
DC COUPLING
An operational amplifier can be configured to shift the signal level according to the analog input voltage range
of the THS1007. The analog input voltage range of the THS1007 goes from 1.5 V to 3.5 V. An operational
amplifier can be used as shown in Figure 38.
Figure 38 shows an example with the analog input signal in the range between −1 V up to 1 V. This signal is
shifted by an operational amplifier to the analog input range of the THS1007 (1.5 V to 3.5 V). The operational
amplifier is configured as an inverting amplifier with a gain of −1. The required dc voltage of 1.25 V at the
noninverting input is derived from the 2.5-V output reference REFOUT of the THS1007 by using a resistor
divider. Therefore, the operational amplifier output voltage is centered at 2.5 V. The 10 μF tantalum capacitor
is required for bypassing REFOUT. REFIN of the THS1007 must be connected directly to REFOUT in
single-ended mode. The use of ratio matched, thin-film resistor networks minimizes gain and offset errors.
1V
0V
−1 V
R₁
1.25 V
R₁
5V
_
+
3.5 V
2.5 V
1.5 V
R_S
C
THS1007
AINP
REFIN
REFOUT
+
R₂
10 μF
R₂
Figure 38. Level-Shift for DC-Coupled Input
DIFFERENTIAL MODE OF OPERATION
For the differential mode of operation, a conversion from single-ended to differential is required. A conversion
to differential signals can be achieved by using an RF-transformer, which provides a center tap. Best
performance is achieved in differential mode.
Mini Circuits
49.9 Ω ^T4−1
R
200 Ω ^C
R
C
THS1007
AINP
AINM
+
10 μF
REFOUT
Figure 39. Transformer Coupled Input
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