Si3210/Si3211/Si3212
overwritten by a new one. There is no buffering of the
digit information.
Audio Path
Unlike traditional SLICs, the codec function is integrated
into the ProSLIC. The 16-bit codec offers programmable
gain/attenuation blocks and several loop-back modes.
The signal path block diagram is shown in Figure 23.
Transmit Path
In the transmit path, the analog signal fed by the
external ac coupling capacitors is amplified by the
analog transmit amplifier, ATX, prior to the A/D
converter. The gain of the ATX is user selectable to one
of mute/–3.5/0/3.5 dB options. The main role of ATX is
to coarsely adjust the signal swing to be as close as
possible to the full-scale input of the A/D converter in
order to maximize the signal-to-noise ratio of the
transmit path. After passing through an anti-aliasing
filter, the analog signal is processed by the A/D
converter, producing an 8 kHz, 16-bit wide, linear PCM
data stream. The standard requirements for transmit
path attenuation for signals above 3.4 kHz are
implemented as part of the combined decimation filter
characteristic of the A/D converter. One more digital
filter is available in the transmit path: THPF. THPF
implements the high-pass attenuation requirements for
signals below 65 Hz. The linear PCM data stream
output from THPF is amplified by the transmit-path
programmable gain amplifier, ADCG, which can be
programmed from –∞ dB to 6 dB. The DTMF decoder
can receive the linear PCM data stream at this point to
perform the digit extraction when enabled by the user.
The final step in the transmit path signal processing is
the user selectable A-law or µ-law compression which
can reduce the data stream word width to 8 bits.
Depending on the PCM_Mode register selection, every
8-bit compressed serial data word will occupy one time
slot on the PCM highway, or every 16-bit
uncompressed serial data word will occupy two time
slots on the PCM highway.
Preliminary Rev. 1.11
39
ETC [ ETC ]
