WM_PRJ_Q2400_PTS_005 -007
18th January 2006
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2.3.2.2 Speaker
outputs
2.3.2.2.1 Common speaker output 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. Moreover 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
Ω
and up to 1 nF
. These outputs are differential and the output power can be
adjusted by step of 2 dB. The output can be directly connected to a speaker.
Differential Connection:
Impedance of the speaker amplifier output in differential mode : R
≤
1
Ω
+/-10 %
SPKxP
SPKxN
Figure 16: Speaker outputs (differential mode)
Single-ended Connection:
Typical implementation:
SPKxP
C1
+
SPKxN
C2
+
ZHP
Speaker
C3
33 to
100 pF
R1
Figure 17: Speaker outputs (single-ended connection)
C1 = from 4.7 µF to 47 µF as per the speaker characteristics and the output
power.
C1=C2; R1= Speaker Impedance.
Nevertheless in a 32
Ω
speaker case, you should use a cheaper and smaller
solution : R1 = 82
Ω
et C2 = 4.7 µF (ceramic).
