User's Manual

SC14CVMDECT Cordless Voice Module
© 2011 SiTel Semiconductor B.V. Company Confidential 36 August 19, 2011 v1.2.1
volume control.
Headset detection boundaries can be adjusted in
EEPROM. When headset indication is received from
the FP headset detection logic (future release), the
Application Software can decide if audio should be
switched to headset and sends a request to the FP.
Tone Handling
The Application Software state machine must control
when to play tones and the volume setting. Custom
melodies can be defined in EEPROM.
7.3 HARDWARE DESIGN GUIDELINES
Within this section general design guidelines for
SC14CVMDECT FP and PP applications are given.
7.3.1 Circuit design Guidelines
For a reference schematic refer to the SC14CVMDECT
reference kit. With the reference kit package a non-
cost optimized reference design is presented.
For a FP hardware design the following hardware parts
will be needed besides the SC14CVMDECT:
• Supply voltage
• Battery charge
• LED and buttons
• Speakerphone
For a PP hardware design the following hardware parts
will be needed besides the SC14CVMDECT:
• Power
• Battery Charger
• Audio:
• Microphone
• Earpiece
• Speaker
• Headset
7.3.2 PCB Design Guidelines
• Because of the presence of the digital radio
frequency burst with 100 Hz time division periods
(TDD noise), supply ripple and RF radiation, special
attention is needed for the power supply and ground
PCB layout.
• Power supply considerations
Both high and low frequency bypassing of the supply
line connections should be provided and placed as
close as possible to the SC14CVMDECT. In order to
get the best overall performance for both FP and PP
applications, a number of considerations for the PCB
has to be taken into account.
• The width of the power amplifier supply line is rec-
ommended to be between 0.8 and 1.2 mm due to
high current peaks during RF bursts.
• Make angle breaks on long supply lines to avoid
resonance frequencies in respect to DECT fre-
quencies. Maximum 8 cm before an angle break
is recommended.
• Supply lines should be placed as far as possible
away from sensitive audio circuits. If it is neces-
sary to cross supply lines and audio lines, it
should be done with right angles between supply
and audio lines/circuits (microphone, ear-speaker,
speakerphone, etc.)
• Ground plane considerations
In order to achieve the best audio performance
and to avoid the influence of power supply noise,
RF radiation, TDD noise and other noise sources,
it is important that the audio circuits on both FP
and PP applications boards are connected to the
GND_ANA pins (analog ground) on the
SC14CVMDECT with separate nets in the layout.
It is advised to provide the following audio circuits
with separate ground nets connected to the
GND_ANA pins:
• Microphone(s)
• Headset microphone and speaker
• Speakerphone (signal grounds)
Depending on the layout it may also be necessary to
bypass a number of the audio signals listed above to
avoid humming, noise from RF radiation and TDD
noise with. It is also important to choose a microphone
of appropriate quality with a high RF immunity (with
built-in capacitor).
• ESD performance
Besides TDD noise, the ESD performance is
important for the end-application. In order to achieve
a high ESD performance supply lines should be
placed with a large distance from charging terminals,
display, headset connector and other electrical
terminals with direct contact to the ESD source.
On a two-layer PCB application it is important to
keep a simulated one layer ground. With a stable
ground ESD and TDD noise performance will always
improve.