Si32172/3/5

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6.2. Loop Closure Detection

The Si32172/3/5 provides a completely programmable loop closure detection mechanism. The loop closure

detection scheme provides two unique thresholds to allow hysteresis, and also includes a programmable

debounce filter to eliminate false detection. A loop closure detect status bit provides continuous status, and a

maskable interrupt bit is also provided.

6.3. Ground Key Detection

The Si32172/3/5 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.

6.4. Ringing Generation

The Si32172/3/5 provides the ability to generate a programmable sinusoidal or trapezoidal ringing waveform, with

or without dc offset. The ringing frequency, wave shape, cadence, and offset are all register-programmable. Three

ringing modes are supported: balanced, unbalanced, and low-power ringing (LPR). Figure 15 illustrates the

fundamental differences between the three ringing modes.

6.5. Polarity Reversal

The Si32172/3/5 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.

6.6. 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 Si32172/3/5 to the reference impedance. Most real or complex two-wire impedances can

be generated with appropriate register coefficients.

6.7. 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.

6.8. Tone Generators

The Si32172/3/5 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.

Figure 15. Ringing Modes

TIP

RING

VBAT

Balanced

VBAT

TIP

RING

LPR

TIP

RING

VBAT

Unbalanced

GND

GND

GND