AN3213 datasheet(55/64 Pages) STMICROELECTRONICS

55 / 64 page

AN3213

FAQs and troubleshooting

Doc ID 17429 Rev 1

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the signal level. A signal coupler (for example, a capacitive coupling) between the

two sides of the distribution transformers may be required.

●

Q: What method of coupling is preferred for medium voltage and low voltage mains line:

capacitive or inductive?

–

A: For MV line, capacitive coupling is preferable for narrow-band PLC. In the case

of an LV line, being the actual line impedance unpredictable because of the

number of electrical devices connected on it, the solution should be an L-C series

resonant circuit tuned at channel frequency, designed to have low Q even with

very low line impedance (below 5

Ω).

●

Q: Is it possible to detect the channel quality through the ST7570 device?

–

A: Yes. Using the ST7570 estimators for SNR0 and SNR1, always available for the

external host, it is possible to evaluate the channel quality over the physical link

between transmitter and receiver.

●

Q: Why use zero crossing synchronization?

–

A: As defined in the IEC61334-5-1 document, the mains zero crossing information

is used to define the bit and frame timing and ensure proper time slot

management.

●

Q: What is the minimum signal-to-noise ratio that the ST7570 can manage?

–

A: A bit error rate (BER) of 10-3 is used as reference. In this condition, the ST7570

shows good receiving performance with a signal-to-noise ratio down to 13 dB at

1200 baud, 50 Hz.

●

Q: When data is being transmitted by the ST7570, is it encoded in some way?

–

A: No. The ST7570 has been developed according to the IEC61334-5-1 standard,

which neither requires nor allows coding for PHY and MAC levels.

●

Q: What could be the main sources of harmonic distortion in the ST7570 transmitted

signal?

–

A: Generally, harmonics can rise up because of: high output current, due to low

line impedance; saturation of magnetic components in the line coupling circuit,

due to either poor dimensioning of the saturation current or to 50 Hz residual

current; capacitive load applied to the power amplifier output; insufficient margin to

the supply rails (low VCC or high output voltage).

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