V1.20 Page 34 of 48 ICM MP CCQ GRM
A55/C55_Hitachi Company Confidential © Copyright Siemens AG 04/03
Functions
Pin
Requirements
Sequence
Audio mode
functions
Four audio amplifiers are integrated to support
these modes:
1. Supply the speaker in the phone with audio
signals including the possibility of
handsfree switch on and off. This is the
AUDIO MONO MODE.
2. Supply the speaker in the phone with
ringing signal (RINGER MODE)
3. Transfer a key click, generated in digital
part to the speaker. (KEY-CLICK
FUNCTION)
4. Supply of stereo head set with stereo
signal with short circuit protection. This is
called the AUDIO STEREO MODE. These
different modes with gain and multiplexing
can be controlled via TWI. Also the output
can be switched to TRI-STATE via TWI
interface.
Audio Mono Mode VREGA
MONO1
MONO2
VREFEX_M
This mode is the main function of the amplifier.
The two amplifiers are used as differential
mono amplifier to drive the speaker in the
phone as external load. This differential
approach allows delivering an optimum of
power to the speaker also in low voltage mode.
Both amplifier paths are inverting amplifiers
with external AC coupling at the input to
compensate offset failures. The gain can be
adjusted with the TWI interface. The output
stage of the amplifiers must be able to drive a
low impedance load as an external speaker for
the handsfree application.
General parameters: Gain can be adjusted for
each channel separately in steps of 1.5dB in
the range of 21dB to –54 dB and in steps of 3
dB in the range of –54dB to –75dB. The signals
for the amplifier are connected via an audio
multiplexer with 3 pairs of input signals.
Ringer function RINGIN In ringer mode the ringing signal is transferred
via the amplifier to the speaker to eliminate the
additional buzzer. The speaker is controlled
with a rectangular signal RINGIN (PinG9). Input
signal is digital signal with variable frequency.
Amplitude is adjusted by TWI register.
For start-up a smaller time constant must be
used to allow a fast switch on behavior. Ringing
function can be started at any time. If the audio
is off, the start-up is done with RINGER time
constant. If audio is starting with AUDIO start-
up, the time constant is switched to RINGER
mode, too. If the audio amplifier is already up
and running, the RINGIN (PinG9) is connected
to the amplifier and audio signal is muted due
to open multiplexer.
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