Production Data

WM2130

WOLFSON MICROELECTRONICS LTD

PD Rev 1.2 April 2001

9

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:

2

REFBF

REFTF

V

V

M

INFS

−

+

=

+

and

2

REFBF

REFTF

V

V

M

INFS

−

−

=

−

Therefore the input signal span is given by:

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:

)

(

−

=

−

INFS

INFS

V

V

REFBF

REFTF

ADC REFERENCE MODES

The WM2130 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 WM2130 internal use and REFTF and REFBF must not be used as voltage

references for any other device in the application.

MODE

PIN

MODE

FUNCTION

COMMENTS

AGND

Full external

REFTS

REFTF

=

REFBS

REFBF

=

On-chip reference generator and reference buffer are

not used.

AVDD/2

Differential

2

REF

V

AVDD

REFTF

+

=

2

REF

V

AVDD

REFTF

−

=

REFTS and REFBS are joined together and connected

either to the negative end of the input signal (true

differential mode) or to the AIN mid-scale voltage

(centre-span mode).

AVDD

Top/Bottom

()

2

REFBS

REFTS

AVDD

REFTF

−

+

=

()

2

REFBS

REFTS

AVDD

REFBF

−

−

=

On-chip reference generator is not used. Reference

buffer centers external reference voltages around

AVDD/2.

Table 1 WM2130 Reference Generation Modes