User's Manual

T-0000-0004-V2.1: Using Mozart II
T-0000-0004-V2.1: Using Mozart II Page: 15 / 24
• Immunity to external perturbations, especially ESD. Note that the standard requires tracking of
demodulation up to 5GHz.
The first precaution to take is to open signals RF-wise, with low value resistors placed as close to the
module connector as possible. This should be done on all GPIOs and I2C lines; in some cases the
resistors would be needed at both ends of the track (if the connected device/part is creating noise
itself, such as certain LCMs).
If DC/DC converters are used – beware of parasitic oscillations at the output stage; snubbers might be
required to stabilize them.
17 Muting and Demodulation Issues
Any device built around a Mozart II module is a complex mixed-signal (digital and analog) system with
RF parts (Wi-Fi and FM). In this kind of system, the main problem is to avoid digital or demodulation
noise coming out to the audio sections.
The module itself has high quality filtering of the power supply for the audio sections. But it is up to the
system designer to make sure the external circuitry (especially audio signal paths and external active
parts) will be immune to power supply noise and to Wi-Fi radio waves.
The latter is very important, because many low-cost or old amplifiers (design-wise) are very prone to
demodulation of RF signals. We strongly recommend to select parts with recent designs and to make
sure with the manufacturer that the selected part is not sensible to the electric fields around 2.4GHz,
otherwise Wi-Fi radio waves will create demodulation noise in the speaker. Even though, we
recommend taking appropriate measures to protect & shield amplifiers properly – mobile phones are
also very likely to generate demodulation noise.
In the case of power operational amplifiers, it is good practice to insert resistors (HF wise, around 4k7)
in the positive and negative lines, as close to the device as possible. While this is not always efficient,
we recommend keeping PCB footprints for those parts.
It is also recommended that the audio tracks are guarded against other signals by sufficient ground
planes.
18 Using Mozart II as a slave companion
Some devices might want to keep their existing designs (control processor, display, buttons…) and
add Internet Radio functionality through the module. This might make sense, but one must not
underestimate the amount of development required to handle all the new features brought in by the
device. It might even prove impossible – scrolling through long lists using one line of text and two
buttons is not a nice user experience.
In fact, the general rule is that the “smartest” part must handle the UI and treat the other one as slave.
For instance, a very basic CD player will never have the level of complexity required by internet radio
features – if one wants to build an “Internet Radio CD player” the way to go is to make a custom
development on Mozart II to have it drive the CD pickup electronics for instance. Other devices might
have a less balanced choice; for those Mozart II has a full software library that can come on top of
several communication links to be remotely controlled by another processor.
The detailed description of this option is beyond the scope of this document. Please contact your
nearest AwoX sales representative for detailed information.
19 Extensions and Customization
The main goal of Mozart II is to allow manufacturers to easily build Internet Radio and network
streaming devices. The fastest way to reach this is to reuse the reference parts & schematics with the