Motorola A920 Service Manual Download

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A920:

RX Audio

Description

Receive audio data is transferred from the POG to the PCAP through the ASAP interface for mono audio and the VSAP interface for stereo audio data. The data is then converted
into an analog form through a 16-bit Stereo DAC or 13-bit phone DAC. The output of PCAP’s internal DAC drives the internal PGA. The output of the PGA can be routed to one
of the four supported outputs via the internal multiplexer. All outputs use the same D/A converter so only one output can be active at one time. The user can adjust the gain of the
audio outputs with the volume control buttons.

The Handset Speaker is driven by PCAP’s internal SPKR differential amplifier. Following the speaker path from the PCAP pins SPKR- and SPKR+, they are routed through
R4004 and R4005 respectively, and then connected to the transducer. Off the SPKR- path, SPKR_IN is routed through C4002 for the inverting input of the speaker amp A1.
SPKR_OUT1 from PCAP is routed through C4000 and C4002 to SPKR- which is the DAC output of the CODEC. SPKR_IN and SPKR_OUT1 will output their respective bias
voltages on these pins during standby times. This is to maintain the voltage across an external coupling capacitor to avoid audio “pops” when the amplifier is enabled.

The headset uses a standard 2.5mm stereo phone jack. The phone will detect the presence of a stereo headset using HS_SPKR_L of the headset jack, which is pulled high by
R4395 and connected to the ST_COMP of PCAP (this is an interrupt of PCAP which gets sent to MCU over the SPI bus). This pin will be pulled to a logic low whenever the ste-
reo headset plug is inserted into the jack. The headset may contain a momentary switch, which is normally closed and is in series with the microphone cartridge. When the
momentary switch is pressed, the bias current being supplied to the microphone will be interrupted. The phone will detect this action and make an appropriate response to this
action, which could be to answer a call, end a call, or dial the last number from scratchpad.

The Headset Speaker is driven by PCAP’s internal Left and Right amplifier. Following the speaker path from the PCAP pins ARight_Out and ALeft_Out, they are routed through
C4356, R4352 and C4306, R4302 respectively, and then connected to the headset jack. Off the ARight _Out path, AR_IN is tapped off through C4354 for the inverting input of
the audio amp ARIGHT. Off the ALeft_Out path, AL_IN is tapped off through C4304 for the inverting input of the audio amp ALEFT.

The External Speaker is connected to pin 15 of J5000 (AUDIO_OUT), the accessory connector for the mobile phone. The audio path is routed through R4400 and C4400 and
connected to EXTOUT of PCAP. The DC level of this Audio_Out signal is also used to externally command the phone to toggle it’s ON/OFF state. The Audio_Out signal con-
nects to PCAP’s ON2 pin via R5053 to provide this capability. When a DC level of <0.4V is applied by an accessory for a minimum of 700 milliseconds on the Audio_Out line,
the phone will toggle it’s ON/ OFF state.

The Loadspeaker is driven by PCAP’s ALRT amplifier (A2). The alert path from the PCAP pins ALRT- and ALRT+ are routed directly to the alert transducer. Off the ALRT-
path, ALRT_IN is routed through R4201 for the inverting input of the alert amp A2. SPKROUT2 from PCAP is routed through C4200 and R4200 to ALRT- which is the DAC
output of the CODEC.

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PCAP

SPKROUT2

ALRT_IN

EXTOUT

Audio Filter

Circuit

ALRT-