SI3215 datasheet(39/118 Pages) SILABS

39 / 118 page

Si3215

Rev. 0.92

2.6. 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 22.

2.6.1. 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 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.

Table 29. Associated Registers for Ring Trip Detection

Parameter

Location

Ring Trip Interrupt Pending

RTIP

Direct Register 19

Ring Trip Interrupt Enable

RTIE

Direct Register 22

Ring Trip Detect Debounce Interval

RTDI[6:0]

Direct Register 70

Ring Trip Threshold

RPTP[5:0]

Indirect Register 16

Ring Trip Filter Coefficient

NRTP[12:0]

Indirect Register 23

Ring Trip Detect Status (monitor only)

RTP

Direct Register 68

Note: The ProSLIC uses registers that are both directly and indirectly mapped. A “direct” register is one that is mapped

directly. An “indirect” register is one that is accessed using the indirect access registers (direct registers 28 through

31).

Table 30. Recommended Ring Trip Values for Ringing

Ringing Frequency

NRTP

RPTP

RTDI

decimal

hex

decimal

hex

decimal

hex

16.667

0200

34 mA

3600

15.4 ms

100

0320

34 mA

3600

12.3 ms

112

0380

34 mA

3600

8.96 ms

128

0400

34 mA

3600

7.5 ms

213

06A8

34 mA

3600

5 ms

256

0800

34 mA

3600

4.8 ms

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