Specifications

WM_PRJ_Q2400_PTS_001 - 003
6th November 2002
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2.11.2 Common speaker outputs characteristics
The connection can be differential or single-ended but using a differential
connection to reject common mode noise and TDMA noise is strongly
recommended. Morover in single-ended mode, ½ of the power is lost
. When
using a single-ended connection, be sure to have a very good ground plane, a
very good filtering as well as shielding in order to avoid any disturbance on the
audio path.
Speaker outputs SPK2 are push-pull amplifiers and can be loaded down to 150
Ohms and up to 1nF (see details in table
Speaker gain vs Max output voltage).
These outputs are differential and the output power can be adjusted by step of
2dB. The output can be directly connected to a speaker.
2.11.2.1.1 Differential Connection
Impedance of the speaker amplifier output in differential mode:
•
R
≤
1
Ω
+/-10%
SPKxP
SPKxN
Figure 3: SPK outputs (single-ended connection)
2.11.2.2 Single-ended Connection
Typical implementation:
SPKxP
C1
+
SPKxN
C2
+
ZHP
Speaker
C3
33 to
100
p
F
R1
Figure 4: SPK outputs (single-ended connection)
C1 = from 4.7µF to 47µF as per the speaker characteristics and the output
power.
C1=C2
R1= Speaker Impedance
Using a single-ended connection also includes losing half of the output power
compared to a differential connection.
Nevertheless in a 32 Ohms speaker case, you should use a cheaper and
smaller solution: R1 = 82 Ohm et C2 = 4.7µF (ceramic)