WM2130

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 1.2 April 2001

16

AIN INPUT DAMPING

The charging current pulses into AIN can make the signal source jump or ring, especially if the

source is slightly inductive at high frequencies. Inserting a small series resistor of 20

Ω or less in the

input path can damp source ringing (see Figure 17). The resistor can be made larger than 20

Ω if

reduced input bandwidth or distortion performance is acceptable.

AIN

V

S

< 20R

Figure 17 Damping Source Ringing Using a Small Resistor

DRIVING THE SAMPLE & HOLD REFERENCE INPUTS

The sample and hold reference inputs (connected to pins REFTS and REFBS) present switched-

capacitor loads similar to the AIN pin, but with smaller capacitors (see Figure 18 below). Note that in

Top/Bottom mode, the internal reference buffer is also driven from REFTS and REFBS and the total

load on these pins is therefore the parallel combination of the sample and hold circuit and the

reference buffer.

REFTS

or

REFBS

AVDD

AGND

Mode = AVDD

V

LAST

C

P1

Internal

Reference

Buffer

CLK

CLK

C

Sample

0.6pF

+

-

C

7pF

Figure 18 Equivalent Circuit of REFTS and REFBS Sample & Hold Inputs