Audio Interface
32 Module Hardware Description January 1, 2006
Important: When implementing a single ended speaker design, it is required to place a series
capacitor and resistor on the speaker output line, as illustrated in Figure 2-20.
The capacitor should be of low tolerance with values of C = 10-22 uF.
The resistor value depends on the speaker application:
- For a handset device, the resistor value should be R = 0
Ω at the design stage, but
may be changed to a different value during audio safety testing, in case attenuation
in the speaker gain is required.
- For a headset device, safety regulations require the resistors value to be R >
2R
L
Ω,
where R
L
is the speaker impedance (eg. 32Ω).
For example, when using a 32Ω speaker the series resistance would be R > 64Ω.
Headset Detection
The G24 operates by default in the basic audio mode with the handset audio path, for DTMF
tones and speech, and the alert loudspeaker device, for rings and alert tones, active.
The headset path is an alternate audio path in basic mode. It is designed for, but not limited to, a
personal hands-free audio device, a headset, using the headset microphone input device and the
speaker output device. When this path is selected, the alert loudspeaker is disabled, and all the
audio sounds are passed through to the headset path.
The HDST_INT_N signal is used to switch between handset and headset audio paths in basic
audio mode. This signal is set high by default at power up. Asserting the HDST_INT_N signal
low enables the headset audio path and disables the handset and alert paths. Setting this signal
high will disable the headset path and enable the handset and alert audio paths.
The G24 supports dynamic switching between the handset and headset audio paths, during
operation and call handling.
Important: The HDST_INT_N signal does not operate in advanced audio mode. This signal's
functionality is overridden by the AT+MAPATH command settings.
Table 2-8:
Speaker Port Specifications
Parameter Conditions Min Typ Max Unit
Output
Voltage
No load
Single ended
2.5 V
PP
Gain Programmable in
3 dB steps
021dB
AC Output
Impedance
32 Ω
DC Voltage 1.38 V
THD 32 Ω load
200 Hz - 20 kHz
0.1 %
Isolation Speech, f> 4 kHz 60 dB
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