THS1007

SLAS286A – AUGUST 2000– REVISED DECEMBER 2002

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31

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 40.

Figure 40 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.

_

+

5 V

R1

R1

RS

3.5 V

2.5 V

1.5 V

THS1007

AINP

REFOUT

R2

R2

1.25 V

1 V

0 V

–1 V

REFIN

+

C

10

µF

Figure 40. 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.

THS1007

AINP

AINM

REFOUT

C

C

R

R

200

Ω

49.9

Ω

Mini Circuits

T4–1

+

10

µF

Figure 41. Transformer Coupled Input