User Guide

RH-25
System Module CCS Technical Documentation
Page 18 ©Nokia Corporation Confidential Issue 1 10/2003
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. Microphone input
lines are ESD protected.
Creating a short circuit between the headset microphone signals generates the hook sig-
nal. 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 1.8V 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 will get half of micbias dc value 1.1 V. This change in DC level will cause the Hook-
Int comparator output to change state, in this case from 0 to 1. The button can be used
for answering incoming calls but not to initiate outgoing calls.
Figure 12: 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 13: 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