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TD_Repair_L2.5_A70_A75_R1.0.pdf Release
1.0
Functions Pin
Requirements
Implementation/Sequence
Audio Stereo
Mode
VDDSTEREO
STEREO1
STEREO2
STEREOM
For stereo mode 2 single ended buffers are used. These
buffers will be supplied by the additional regulator with 2.9
Volt to be more stable against the GSM ripple on the battery
voltage. Also reference voltage for the buffers is generated by
a high precision, low noise bandgap reference for better
performance. An external capacitor is needed to filter this
reference additionally. The gain steps for the programmable
gain amplifier are identical with the mono amplifier.
Nokeyclick and ringer needed for the stero part. Gain can be
controlled with the TWI. The connected speaker has an
impedance of typical 16 Ohm. To guarantee a ANTI-POP
noise a digital startup is implemented. This will allow a soft
start of the VMID and creates a “clean” audio band during the
startup. For eliminating external coupling capacitors for the
speaker, an additional amplifier creates virtual ground (for
both speakers). Accordingly to this, the max current of the
virtual ground has to be the double of the normal output
amplifier. Due to the power amplifier offset a DC current
appear in the headset. 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
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.
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 behaviour. 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 is connected
to the amplifier and audio sigal is muted due to open
multiplexer.
Key click
function
Pushing a key of the phone can be combined with a key click.
This function is also realized with the audio amplifier in pulsed
mode. The ASIC creates a digital PWM signal. Frequency of
the PWM signal is 3.5 kHz.
The start-up is similar to the ringer function. If the audio is off,
the start-up is done with KEYCLICK time constant. If audio is
starting with AUDIO start-up, the time constant is switched to
KEYCLICK mode, too. If the audio amplifier is already up and
running, the KEYCLICK is connected to the amplifier and
audio sigal is muted due to open multiplexer.
Audio Multiplex
Matrix
AUDIOA1
AUDIOA2
AUDIOB1
AUDIOB2
AUDIOC1
AUDIOC2
Each of the three input sources should be switched to Mono
and Stereo outputs. Furthermore a conversion can be done.
Following sources:
-
Mono differential
-
Mono Single Ended (both channels parallel)
-
Stereo
The DAC can be switched off for using the analog external
inputs. This principle will allow to do each combination and
have different modes for stereo and mono in parallel.
