C2.5X6.3MM-RAD datasheet(27/38 Pages) SILABS

27 / 38 page

Preliminary Rev. 0.33

Si3226/7

Si3208/9

4.8. Ground Key Detection

The Dual ProSLIC provides a ground key detect

mechanism using a programmable architecture similar

to the loop closure scheme. The ground key detect

scheme provides two unique thresholds to allow

hysteresis and also includes a programmable debounce

filter to eliminate false detection. A ground key detect

status bit provides continuous status, and a maskable

interrupt bit is also provided.

4.9. Ringing Generation

The Dual ProSLIC provides the ability to generate a

programmable

sinusoidal

trapezoidal

ringing

waveform, with or without dc offset. The ringing

frequency, wave shape, cadence, and offset are all

scheme, the ringing signal is applied to both the TIP and

RING leads using dual ringing waveforms that are 180°

out of phase with each other. The resulting ringing

signal seen across TIP-RING is twice the amplitude of

the ringing waveform on either the TIP or RING lead,

which allows the ringing circuitry to be forced to

withstand only half the total ringing amplitude seen

across TIP-RING.

4.10. Polarity Reversal

The Dual ProSLIC supports polarity reversal for

message waiting and various other signaling modes.

The ramp rate can be programmed for a smooth or

abrupt transition to accommodate different application

requirements.

4.11. Two-Wire Impedance Synthesis

The ac two-wire impedance synthesis is generated on-

chip using a DSP-based scheme to optimally match the

output impedance of the Dual ProSLIC to the

impedance of the subscriber loop and minimize the

receive path signal reflected back onto the transmit

path. Most real or complex two-wire impedances can be

generated by using the coefficient generator software to

simulate the desired line conditions and generate the

required register coefficients.

4.12. Transhybrid Balance Filter

The trans-hybrid balance function is implemented on-

chip using a DSP-based scheme to effectively cancel

the reflected receive path signal from the transmit path.

The coefficient generator software is used to optimize

the filter coefficients.

4.13. Tone Generators

The Dual ProSLIC includes two digital tone generators

that allow a wide variety of single- or dual-tone

frequency and amplitude combinations. Each tone

generator has its own set of registers that hold the

desired frequency, amplitude, and cadence to allow

generation of DTMF and call progress tones for different

requirements. The tones can be directed to either

receive or transmit paths.

4.14. DTMF Detection

In DTMF, two tones generate a DTMF digit. One tone is

chosen from the four possible row tones, and one tone

is chosen from the four possible column tones. The sum

of these tones constitutes one of 16 possible DTMF

digits. The Dual ProSLIC performs DTMF detection

using an algorithm to compute the DFT for each of the

eight DTMF frequencies and their second harmonics. At

the end of the DFT computation, the squared

magnitudes of the DFT results for the 8 DTMF

fundamental tones are computed. The row and column

results are sorted to determine the strongest tones, and

checks are made to determine if the strongest row and

column tones constitute a DTMF digit.

4.15. DC-DC Controller

The controller converts a single positive dc input voltage

into an independent negative battery voltage for each

channel. The controller operates a dc-dc converter

circuit that converts a single positive dc input voltage

into an independent negative battery voltage for each

channel. In addition to eliminating external high-voltage

power supplies, the dc-dc controller allows the Dual

ProSLIC to dynamically control the battery voltage to

the minimum required for any given operating state

according to the programmed linefeed parameters.

4.16. Wideband Audio

The Si3226 supports a narrowband (200 Hz–3.4 kHz)

audio codec. The Si3227 supports a software-

selectable wideband (50 Hz–7 kHz) and narrowband

(200 Hz–3.4 kHz) audio codec. The Si3227 wideband

mode provides an expanded audio band at a 16-bit,

16 kHz sample rate for enhanced audio quality while

maintaining standard telephony audio compatibility.

Wideband audio samples are transmitted and received

on the PCM interface using two consecutive 8 kHz

frames.

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