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TECHNICAL DESCRIPTION
Issue 1
Section 4
PMCD030901C8
Revision 0
– 18 –
Service Manual
4.6. SYREN
4.6.1
Introduction
SYREN U120 contains the interace circuits to the audio, RF and auxiliary analogue functions. It is configured using the TSP
on and interfaces with the DSP in via the voice and I & Q interfaces.
Figure 4.9: SYREN Device U120
4.6.2
Power Amplifier Ramp (APC)
The purpose of the Automatic Power Control is to generate an envelope signal to control the power ramping up, ramping
down and power level of the radio burst.
It includes a DAC and RAM in which the shape of the envelope (ramp-up and ramp-down) are stored digitally. The envelope
signal is converted to analogue by a 10-bit DAC. RF requirements determine the co-efficient of the ramp shape.
Timing of the APC is generated internally and is dependent on real time signals from TSP and the content of two registers
which control the relative position of the envelope signal versus the modulated I & Q.
4.6.3
Audio
SYREN provides the analogue interface for the digital audio samples processed by the DSP in . A 16mm 8
Ω
speaker mounted on the back of the handset is used both for playing ring tones and for desktop handsfree (DTHF) functions.
The personal handsfree (PHF) headset connects directly to the HSO (earpiece) and HSMIC (microphone) pins of the SYREN
device. Bias for the microphone is provided by HSMICBIAS from SYREN. Detection of PHF connection is made by an
interrupt on IO(2) of . A small delay is applied before HSOVMID bias voltage is activated to minimise noise heard
in the headset when HSO is enabled. This voltage controls transistor TR402 which delays the bias at the headset connector.
Melodies and simple ring tones are produced by Melody Generator U301 which outputs these to both the DTHF speaker and
to AUX1 of SYREN. The audio feed to SYREN allows ring tones and melodies to be played at a lower level through the PHF
headset. U301 is controlled via the microwire interface with an interrupt signal to indicate when its FIFO buffers
are empty.
4.6.4
LED Driver
SYREN contains an open collector type output for the Charge LED control. The default state is ON to enable indication of
charging in the case of a deeply discharged battery.
10694-1
U100
CALYPSO
U120
SYREN
DSP
APC
VOICEBAND I/F
U301
MELODY
GENERATOR
SIDETONE
MICROPHONE
RECEIVER
DTHF SPEAKER
PERSONAL
HANDSFREE
(PHF)
PARAMP
APC (U605)
MICBIAS
HSMICBIAS
HSVMID
HSO
TR402
nPHF±DET
nPHF±DET