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+12V

-12V

THS4031

2200pF

(+)IN

+VIN

+12V

-12V

THS4031

(-)IN

+0Vto+4V

+2.048V

R

C

1

F

m

1

F

m

1

F

m

1

F

m

1

F

m

1

F

m

5 W

75 W

300 W

300 W

5 W

ADS8472

SLAS514 – DECEMBER 2006

PRINCIPLES OF OPERATION (continued)

Figure 41. Single-Ended Input, Differential Output Configuration

In systems, where the input is differential, the THS4031 can be used in the inverting configuration with an

additional DC bias applied to its + input so as to keep the input to the ADS8472 within its rated operating voltage

range. The DC bias can be derived from the REF3220 or the REF3240 reference voltage ICs. The input

configuration shown below is capable of delivering better than 97dB SNR and -103db THD at an input frequency

of 100 kHz. In case band-pass filters are used to filter the input, care should be taken to ensure that the signal

swing at the input of the band-pass filter is small so as to keep the distortion introduced by the filter minimal. In

such cases, the gain of the circuit shown below can be increased to keep the input to the ADS8472 large to

keep the SNR of the system high. Note that the gain of the system from the + input to the output of the

THS4031 in such a configuration is a function of the gain of the AC signal. A resistor divider can be used to

scale the output of the REF3220 or REF3240 to reduce the voltage at the DC input to THS4031 to keep the

voltage at the input of the converter within its rated operating range.

22

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