WM8351 datasheet(64/330 Pages) WOLFSON

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WM8351

Production Data

PD, April 2012, Rev 4.5

13.4 INPUT SIGNAL PATH

The WM8351 has multiple analogue inputs. There are two input channels, Left and Right, each of

which consists of an input PGA stage followed by a boost/mix stage switch into the hi-fi ADC. Each

input PGA path has three input pins which can be configured in a variety of ways to accommodate

single-ended, differential or dual differential microphones. There are two auxiliary input pins which

can be fed into to the input boost/mix stage as well as driving into the output path. A bypass path

exists from the output of the boost/mix stage into the output left/right mixers.

13.4.1

MICROPHONE INPUTS

The microphone inputs of the WM8351 are designed to accommodate electret condenser

microphones or analogue line-in signals. They comprise the following pins:



IN1LP: first non-inverting input, left channel



IN2L: second non-inverting input, left channel



IN1LN: inverting input, left channel



IN1RP: first non-inverting input, right channel



IN2R: second non-inverting input, right channel



IN1RN: inverting input, right channel

The non-inverting inputs have constant input impedance to VMID, whereas the inverting input’s

impedance varies with the pre-amplifier’s gain. (Note: the terms “inverting” and “non-inverting” refer to

the microphone pre-amplifiers only. For overall behaviour, the inverting record mixer and the ADC,

whose output can optionally be inverted in the digital domain, must also be taken into account.)

Each channel has a programmable pre-amplifier, which supports single-ended or pseudo-differentially

connected microphones. The amplified signal for each channel can be digitised in the audio ADC

and/or mixed into the output signal path.

Figure 37 Microphone Inputs and Pre-amplifiers

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