WM8951L datasheet(18/42 Pages) WOLFSON

18 / 42 page

WM8951L

Production Data

PD Rev 4.1 December 2007

Recommended component values are C1 = 220pF (npo ceramic), C2 = 1

µF, R1 = 680 ohms, R2 =

47k. Rmic values depends on gain setting (see above).

R1 and R2 form part of the biasing network (refer to Microphone Bias section below). R1 connected

to MICBIAS is necessary only for electret type microphones that require a voltage bias. R2 should

always be present to prevent the microphone input from charging to a high voltage which may

damage the microphone on connection. R1 and R2 should be large so as not to attenuate the signal

from the microphone, which can have source impedance greater than 2k. C1 together with the

source impedance of the microphone and the input impedance of MICIN forms an RF filter. C2 is a

DC blocking capacitor to allow the microphone to be biased at a different DC voltage to the MICIN

signal.

MICROPHONE BIAS

The MICBIAS output provides a low noise reference voltage suitable for biasing electret type

microphones and the associated external resistor biasing network. Refer to the Microphone Input

section for an application drawing and further description.

The scheme for MICBIAS is shown in Figure 13. Note that there is a maximum source current

capability of 3mA available for the MICBIAS. This limits the smallest value of external biasing

resistors that can safely be used.

Note that the MICBIAS output is not active in standby mode.

VMID

MICBIAS

AGND

Figure 13 Microphone Bias Schematic

ADC

The WM8951L uses a multi-bit oversampled sigma-delta ADC. A single channel of the ADC is

illustrated in the Figure 14.

FROM MICROPHONE

INPUT

FROM LINE INPUT

ANALOG

INTEGRATOR

INSEL

MULTI

BITS

TO ADC DIGITAL FILTERS

Figure 14 Multi-Bit Oversampling Sigma Delta ADC Schematic

WM8951L Datasheet(PDF) 18 Page - Wolfson Microelectronics plc