Specifications

TC35 / TC37 Hardware Interface Description
TC35_37_HD_02_V03.10 - Released Page 43 of 92 21.12.2001
3.6.1 Speech processing
The voiceband filter includes a digital interpolation low-pass filter for received voiceband
signals with digital noise shaping and a digital decimation low-pass filter for voiceband
signals to be transmitted.
After voiceband (interpolation) filtering the resulting 2Mbit/s data stream is digital-to-analog
converted and amplified by a programmable gain stage in the voiceband processing part.
The output signal can directly be connected to the earpiece of the GSM cellular device or to
an external handset earpiece (via I/O connector). In the opposite direction the input signal
from the microphone is first amplified by a programmable amplifier. After analog-to-digital
conversion a 2Mbit/s data stream is generated and voiceband (decimation) filtering is
performed.
The resulting speech samples from the voiceband filters are handled by the DSP of the
baseband controller to calculate e.g. amplifications, sidetone, echo cancellation or noise
suppression.
Full rate, half rate and enhanced full rate, speech and channel encoding including voice
activity detection (VAD) and discontinuous transmission (DTX) and digital GMSK modulation
are also performed on the GSM baseband processor.