WM8991 datasheet(40/174 Pages) WOLFSON

40 / 174 page

WM8991

Pre-Production

PP, May 2008, Rev 3.1

MICROPHONE INPUTS

Up to four microphones can be connected to the WM8991, either in single-ended or pseudo-

differential mode. A low noise microphone bias is fully integrated to reduce the need for external

components.

In single-ended microphone input configuration, the microphone signal is connected to the inverting

input of the PGA (LIN1, LIN3, RIN1 or RIN3). The non-inverting input of the PGAs should be

internally connected to VMID in this configuration. This is enabled via the Input PGA configuration

inputs or ADC bypass inputs.

In pseudo-differential microphone input configuration, the non-inverted microphone signal is

connected to the non-inverting input of the PGA (LIN2, LIN4, RIN2 or RIN4) and the inverted (or

noisy ground) signal is connected to the inverting input (LIN1, LIN3, RIN1 or RIN3).

Any PGA input pin that is used in either microphone configuration should not be enabled as a line

input path at the same time.

The gain of the input PGAs is controlled via register settings. Note that the input impedance of LIN1,

LIN3, RIN1 and RIN3 changes with the input PGA gain setting, as described under “Electrical

Characteristics”. (Note this does not apply to input paths which bypass the input PGA.) The input

impedance of LIN2, LIN4, RIN2 and RIN4 does not change with input PGA gain. The inverting and

non-inverting inputs are therefore not matched and the differential configuration is not fully

differential.

Figure 17 Single-Ended Microphone Input

Figure 18 Differential Microphone Input

WM8991 Datasheet(PDF) 40 Page - Wolfson Microelectronics plc