THS12082_09 Datasheet, PDF (28/42 Pages) Texas Instruments – 12-BIT, 8 MSPS, SIMULTANEOUS SAMPLING ANALOG-TO-DIGITAL CONVERTERS

THS12082
12-BIT, 8 MSPS, SIMULTANEOUS SAMPLING ANALOG-TO-DIGITAL CONVERTERS
SLAS271B – MAY 2000 – REVISED DECEMBER 2002
dc coupling
An operational amplifier can be configured to shift the signal level according to the analog input voltage range
of the THS12082. The analog input voltage range of the THS12082 goes from 1.5 V to 3.5 V. An operational
amplifier specified for 5-V single supply can be used as shown in Figure 17.
Figure 17 shows an application example where the analog input signal in the range from –1 V up to 1 V is shifted
by an operational amplifier to the analog input range of the THS12082 (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 THS12082 by using a resistor divider.
Therefore, the op-amp output voltage is centered at 2.5 V. The use of ratio matched, thin-film resistor networks
minimizes gain and offset errors.
1V
0V
–1 V
R
1.25 V
R
5V
_
+
3.5 V
2.5 V
1.5 V
RS
THS12082
AINP
REFIN
REFOUT
R
R
Figure 17. 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
T4–1
49.9 Ω
R
200 Ω ^C
R
C
THS12082
AINP
AINM
REFOUT
Figure 18. Transformer Coupled Input
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