User's Manual

WM_PRJ_Q2400_PTS_002 - 004
March 5, 2004
2.13.2 Speaker outputs
2.13.2.1 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 SPK1 and SPK2 are push-pull amplifiers and can be loaded down to 150 Ohms
and up to 1 nF (see details in table Speaker gain vs Max output voltage).
Impedance of the speaker amplifier output in differential mode is :
R ≤ 1Ω +/-10 %.
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.
Using a single-ended connection also includes losing half of the output power compared to a
differential connection.
The gain of the speaker outputs is internally adjusted and can be tuned using an AT command.
Speaker gain vs Max output voltage
Receive Gain (dB) (*) Max output level (Vrms)
Max.speaker load (Ω)
+2 1.74 150
0 1.38 50
-2 1.099 32
-4 0.873 32
-6 0.693 32
-8 0.551 32
-10 0.437 32
-12 0.347 32
-14 0.276 32
-16 0.219 32
-18 0.174 32
-20 0.138 32
-22 0.110 32
-24 0.087 32
-26 0.069 32
(*) analog gain: might not be significant
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