THS1206

SLAS217H – MAY 1999 – REVISED JULY 2003#

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36

DC COUPLING

An operational amplifier can be configured to shift the signal level according to the analog input voltage range of the

THS1206. The analog input voltage range of the THS1206 goes from 1.5 V to 3.5 V. An op-amp specified for 5-V single

supply can be used as shown in Figure 42.

Figure 42 shows an application example where the analog input signal in the range from –1 V up to 1 V is shifted by an

op-amp to the analog input range of the THS1206 (1.5 V to 3.5 V). The op-amp 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 THS1206 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.

_

+

5 V

R

R

RS

3.5 V

2.5 V

1.5 V

THS1206

AINP

REFOUT

R

R

1.25 V

1 V

0 V

–1 V

REFIN

Figure 42. 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.

THS1206

AINP

AINM

REFOUT

C

C

R

R

200

Ω

49.9

Ω

Mini Circuits

T4–1

Figure 43. Transformer Coupled Input