Audio Signal Interface - Sierra Wireless MC5725 Hardware Integration Manual

Rev 1.9.1 Feb.09
In the event of a discrepancy in values between this guide and the Product Specification Document (PSD), the PSD takes precedence.
Table 4-3: Echo cancellation details
Mode
Speakerphone
Off

Audio signal interface

The differential microphone input offers superior noise
rejection performance to the single‐ended approach. The
termination of the differential pair rejects common signals
(such as noise). The pair should be routed together for optimal
noise rejection. Since MIC_P and MIC_N are high impedance
inputs, it is important to isolate these from possible noise
sources (toggling digital lines with fast edges).
The speaker interface can be single‐ended or differential
depending on product. Single‐ended speaker outputs rely on
modem ground as an audio reference.
The audio passband for both receive and transmit paths
(speaker and microphone) extends from 300 Hz to 3.4 kHz. A
programmable sidetone with a range from mute to unity gain
is available for both headset and main audio paths. Sidetone
should be muted for speakerphone use.
Note that certain carriers now require use of hearing‐aid
compatible transducers in a handset design. The Primary
audio path can be interfaced directly to such devices. Refer to
ANSI C63.19 for details regarding reduced RF emissions (ʺU3
ratingʺ) and inductive / telecoil coupling (ʺU3Tʺ rating)
devices.
Table 4-4: Primary audio signal interface
Signal Pin #
MIC_P 1
MIC_N 3
Proprietary and Confidential
Long echo path (<64 ms travel time from speaker to
•
microphone)
Loud echo
•
• For use with speakerphone applications with high
distortion
• Half-duplex algorithm, very aggressive in near-end
Tx muting to eliminate transmitted echo
Type Directions
Analog Input
Analog Input
Audio Interface
Details
Description
Non-inverted
microphone input (+)
Inverted microphone
input (-)
57