Nordic Star Products NRD24V1 - Manual (Page 11)

Revision 1.0 Page 11 of 25
Headset Reference Design v1.0
3.2.1.1 Headset interface
The loudspeaker(s) are driven differentially, and need some filtering due to the class D output amplifier of
the audio codec. Figure 7. ”Loudspeaker interface” shows a typical filter network that can be used for driv-
ing a headset loudspeaker. The filter depends on the chosen loudspeaker.
The microphone can be connected directly to the codec input. The codec input has a 1.1 V supply that can
power a typical headset microphone.
Figure 7. Loudspeaker interface
3.2.1.2 PC interface
The differential loudspeaker output from the codec must be connected single ended to the PC microphone
input and the PC loudspeaker output must be connected to the codec microphone input to interface with a
PC audio port. Figure 8. ”PC input interface” shows the networks that accommodate this. The loudspeaker
output from the PC must be level adjusted and a network as shown in Figure 9. ”PC output interface” used.
Figure 8. PC input interface
L2
470u
C4
100p
C1
100p
R1
56
R2
56
C2
4.7u
C3
4.7u
L1
470u
AOUTP
AOUTN
R7
4.7k
R8
4.7k
C8
2.2u
C9
2.2u
C5
10n
C7
100n
R9
22k
R4
22k
R6
22k
R5
22k
C6
10u
+
-
V-
V+
U1
LM7301
3
4
1
2
5
R3
1k
PC microphone input
L2
470u
C4
100p
C1
100p
R1
56
R2
56
C2
4.7u
C3
4.7u
L1
470u
AOUTP
AOUTN