Earpiece
The earpiece to be used in RM-25 is an 8-mm Pico earpiece produced by Philips Speaker Systems. It has 32ohm
continuous impedance and continuous power 8 mWatts. It is driven by differential signals from UEME (EARP &
EARN). It makes contact with the PWB via spring contacts.
Microphone
The microphone module for RM-25 is used Pop-Port
TM
microphone module. Its sensitivity is -42dB Nominal.
Contacts are done by springs.
Two inputs are used from UEME, one for the normal internal microphone and the other for the headset. The
third microphone input is not used, so it is connected to ground via capacitors. Microphone bias block in UEME
generates bias voltages for handportable and handsfree/headset microphones. For both microphone bias
outputs (MICB1 & MICB2), the minimum output voltage is 2.0 Volts and maximum output current is 600 mA.
Microphone bias block also includes a low pass filter for the reference voltage used as an input for the MICB1&2
amplifiers.
IHF amplifier and speaker
The speaker to be used in RM-25 is a 16mm 8ohm speaker. It can handle 0.3 Watts nominal power and short
trem peak power of 0.8 Watts. The component is housed in the antenna housing and connects to the PWB via
spring contacts.
PAOUTP and PAOUTN lines of UEME are use to drive Boomer IHF amplifier.
Power amplifier is a differential opamp. The differential output drives the HandsFree speaker. HandsFree
amplifier load impedance is 8 ohm.
The outputs go into a high impedance state when powered down. The amplifier can be enabled and shut down
using a GENIO line from UPP_WD2.
SW controls IHF, headset and earpiece volume via UEME. Gain setting can be done in 2 dB steps, from –40 to +6
dB. The output sound pressure level of the internal HandsFree speaker is controlled by SW (CBus is used for
controlling).
The schematic around the Boomer IHF amplifier is presented in RM-25 schematics. The schematic shows all the
filtering needed and also protection components against ESD and EMC. The EMC and ESD filtering component
must be as near as possible to the earphone pads of the phone.
The supply voltage for the IHF amplifier is taken directly from the battery voltage.
External audio interface
In RM-25 there is a Pop-Port
TM
connector which is fully differential 4–wire connection.
Figure 163 External audio connector
RM-25
System module
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