2.
Overview
The codec board is powered by an on-board 3.3V regulator to reduce noise to a minimum. The
PCM control signals for the codec go directly to the
Bluetooth
module on the motherboard via the
10-way connector, as do the 3 push button switches. This allows the switches to be used with
an external program that implements the upper portion of headset or Handsfree profile.
The microphone input, designed to interface to PC compatible headsets, has a fixed gain of 16
set by external components to the codec (the amplifier itself is part of the codec). Part of the
microphone signal is mixed into the headphone output signal via VR2. This feature is known as
“sidetone” and allows the user to hear their own voice when speaking. It is commonly used in
telephony applications to give the user the necessary audio feedback that their ears expect.
The audio output gain is by default fixed at 1. By fitting VR1, the audio gain can be made
adjustable.
The 120mW stereo output amplifier U3 ensures that the codec board can drive standard 32
Ω
stereo headphones while keeping total harmonic distortion down to 0.1%.
Component Placement
Note that not all
components are fitted –
non-fitted components are
shown without pads. Refer
to Section 7 for details of
component fitment and
specification.
APN_06002_1v03 Winbond Audio Board Application Note
3