User Guide

RM-11
System Module CC Technical Documentation
Page 18 ©2004 Nokia Corporation Confidential Issue 1 02/2004
External Microphone Connection
The external microphone input is fully differential and lines are connected to the UEM
microphone input (MIC2P/N). The UEM (MICB2) provides bias voltage. The microphone
input lines are ESD protected.
Creating a short circuit between the headset microphone signals generates the hook
signal. When the accessory is not connected, the UEM resistor pulls up the HookInt
signal. When the accessory is inserted and the microphone path is biased the HookInt
signal decreases to 1.8 V due to the microphone bias current flowing through the
resistor. When the button is pressed, the microphone signals are connected together and
the HookInt input receives half of micbias DC value 1.1 V. This change in DC level causes
the HookInt comparator output to change states, in this case from 0 to 1. The button can
be used for answering incoming calls but not to initiate outgoing calls.
Figure 13: External microphone connection
External Earphone Connection
Headset implementation uses separate microphone and earpiece signals. The accessory is
detected by the HeadInt signal when the plug is inserted.
Figure 14: External earphone and IHF connections
UEM
MICB2
MIC2P
MIC2N
HookInt
EMC/ESD
XMICP
XMICN
UEM
XEAR
MIC3P
MIC3N
EMC/ESD
Ct
Rout+
Rout-
Lout+
Lout-
SPKRout+
SPKRout-
PhoneIN (IHF)
Rin
Lin
A
udio Amplifier
VAFR
VAFL
FM Radio
PhoneIN (HS)
IHF Speaker