Si32172/3/5

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Rev. 1.0 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • August 31, 2021

6.13. In-Circuit and Metallic Loop Testing (MLT)

A rich set of features is provided for in-circuit testing of the FXS system and the connected telephone line (MLT):

 Tone generators

 Audio diagnostic filters

 Digital and analog loop-back modes

 Internal test load

 Monitor ADC

 DSP algorithms

Using these facilities, it is possible to test the Si32172/3/5’s dc-dc converter, codec, line-feed, ISI bus interface,

DSP, and call progress state-machine as well as testing the connected telephone line and external protection

circuitry.

The audio diagnostic filters on the FXS are intended to provide programmable filtering of the TX digital audio signal

and calculate the peak and/or average signal power of the filters’ outputs. The signal powers are then compared to

programmable thresholds. The programmable filters can be used to band-pass filter a certain tone or notch out

certain tones, so that the signal power measurements are frequency selective. This filtering is useful in a telephony

system because it can measure harmonic distortion, intermodulation, noise, etc.

The Si32172/3/5 incorporates an internal test load with a 2.2 k

 nominal value that can be connected across

Tip/Ring (Figure 16). The audio diagnostics system and built-in test load can be used to test the FXS interface

(Si32172/3/5) itself without requiring an external load, a connected line, or any relays. This facility can be used for

production and in-service testing of such things as:

 Dial tone draw/break

 Audio quality measurements

 Pulse digit detection

 DC feed

 Ringtrip

 Polarity reversal

 Transmission loss

MLT, e.g., GR-909, is facilitated by the built-in DSP, monitor ADC, and test load. They provide the ability to detect

multiple fault conditions within the CPE as well as on the Tip/Ring pair (T-R). Thirteen different measured and/or

calculated parameters are reported by the Monitor ADC. Host software for use in conjunction with the ProSLIC API

is available from Skyworks Solutions. Typical MLT tests include:

 Hazardous Potential Test – This checks for ac voltage > 50 VRMS or dc voltage > 135 V between Tip and

Ground (T-G) or Ring and Ground (R-G).

 Foreign Electromotive Force Test – Checks T-G or R-G for ac voltage > 10 VRMS or dc voltage > 6 V. Uses

same threshold as for hazardous voltage test.

 Resistive Faults Test – Checks for dc resistance from T-R, T-G or R-G. Any measurement < 150 k

 is

considered a resistive fault.

 Receiver-Off-Hook Test – Distinguishes between a T-R resistive fault and an off-hook condition.

 Ringers Test – Measures the magnitude of the connected ring load (REN) across T-R. Results are > 0.175 REN

and < 5 REN for a valid load

 AC Line Impedance (line length) – T-R, T-G, and R-G. Generates a tone at several specific frequencies (audio

band) and measures the reflected signal amplitude (complex spectrum) that comes back (with transhybrid

balance filter disabled). The reflected signal is then used to calculate the line impedance based on certain

assumptions of wire gauge, etc.

 Line Capacitance – T-R, T-G, R-G. Generates a linear ramp function with polarity reversal, and measures the

time constant.