WM2331

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 1.4 April 2001

10

PROGRAMMABLE-GAIN AMPLIFIER

()

M

IN

P

Q

V

V

Gain

V

Gain

V

−

×

=

×

=

The PGA gain defaults to 1.0 at power-up, but can be programmed from 0.5 to 4.0 in steps of 0.5.

ANALOGUE-TO-DIGITAL CONVERTER

2

REFBF

REFTF

V

QFS

−

=

+

and













−

−

=

−

2

REFBF

REFTF

V

QFS

SIGNAL CHAIN SUMMARY

Combining the above equations and referring back to the input, the positive and negative full-scale

voltages at the AIN pin are:

Gain

REFBF

REFTF

V

V

M

INFS

×

−

+

=

+

2

and

Gain

REFBF

REFTF

V

V

M

INFS

×

−

−

=

−

2

Therefore the input signal span is given by:

Gain

REFBF

REFTF

V

V

INFS

INFS

−

=

−

−

+

In order to match the ADC input range to the input signal amplitude, REFTF and REFBF should be

set such that:

Gain

V

V

REFBF

REFTF

INFS

INFS

×

−

=

−

−

+

)

(

ADC REFERENCE MODES

The WM2331 supports three basic modes of reference generation, selected by the voltage applied to

the MODE pin. These are summarised and explained in Table 1.

In differential, Centre Span and Top/Bottom modes, the internally generated ADC references are

intened solely for WM2331 internal use and REFTF and REFBF must not be used as voltage

references for any other device in the application.