Physical performance validation script results help to determine if a design is
comparable with the Microchip reference designs. These tests allow detection of possible
fails in the PLC reception or transmission paths associated with an incorrect PCB
layout, incorrect component selection, etc.
Generally speaking, the most important result is the Frame Error Rate
that represents the number of frames with errors received in the function of the
attenuation (ATT) on the path or, more generally, depending on the received signal
strength indication (RSSI).
The analysis of TX path results helps to determine:
Transmission Power: Depending on
the RSSI value obtained in the results, we can evaluate if the board is
transmitting the expected power. If the setup attenuation configuration is the
same, the RSSI of the received frames from DUT will be similar to the results
for the Microchip reference platform when the power supply source of the power
amplifier is the same (12V by default). Figure 4-11. Typical RSSI Versus
Attenuation on CEN_A with Microchip Reference EKs
On a clean environment setup, the
TX path helps to analyze the transmission linearity of the DUT comparing the
SNR_Payload, SNR Background or the LQI average for the same RSSI signal.
Differences can be found mainly because of the transformer response on an
isolated device but also there are no linear or ideal components, like coils,
protection diodes or varistors, if no Microchip reference design BOM is
selected.
On a similar calibration and
transmission path, the TX_RMSCALC values must be similar as on Microchip
reference boards. Otherwise it is highly recommended to calibrate transmission
parameters using Physical TX Calibration.
The analysis of the RX path results helps to determine:
Sensitivity: Depending on the FER
vs RSSI value obtained on the results, it can be determined if the background
noise of the DUT is lower to the limit to pass G3-PLC certification.
Important: The G3-PLC
certification Sensitivity Performance Test defines a maximum of 5% FER at 60
dBuV of RSSI when running the ROBO Differential modulation.
According
to the Microchip experience, on a typical meter device connected to AC
mains:
Sensitivity (dBuV)
RESULT
<= 45
VERY GOOD
45 < TotalNoise <=
52
GOOD
52 < TotalNoise <=
58
POOR
>58
POTENTIAL ISSUES
Impulsive Noise: Regarding Noised
Symbols, it can be determined if there is impulsive noise on the reception.
Additionally, comparing SNR Worst Symbol or SNR Impulsive with the SNR Payload,
its influence can be determined. It causes errors in symbols so, a frame can be
discarded depending on the impulsive intensity and the length of the frame
increasing the frame error rate.Figure 4-12. Typical SNR Worst
Symbol Versus RSSI on CEN_A Using DBPSK with Microchip Reference
EKsFigure 4-13. Typical SNR Impulsive
Versus RSSI on CEN_A Using DBPSK with Microchip Reference EKsFigure 4-14. Typical SNR Payload
Versus RSSI on CEN_A Using DBPSK with Microchip Reference EKs
Narrowband Noise: Regarding
Corrupted Carriers, it can be determined if there is narrowband noise on the
reception. Additionally, comparing SNR Worst Carrier or SNR BE with the SNR
Payload, its influence can be determined. This kind of noise is continuous and
could be identified by accessing the SQLite database and analyzing the
RX_SNR_CARRIER result values for each frame sent. It could be identified too on
a clean environment when the G3-PLC Tone Map parameter does not correspond with
the expected. It can be analyzed with tools like Noise Test.Figure 4-15. Typical SNR Worst
Carrier Versus RSSI on CEN_A Using DBPSK with Microchip Reference
EKsFigure 4-16. Typical SNR BE Versus
RSSI on CEN_A Using DBPSK with Microchip Reference EKs
White Noise: If there is only
white Gaussian noise during the test, the SNR payload, the
SNR impulsive, the SNR be and the
SNR background are similar. It is not critical in terms of
the reception (because it applies to the complete bandwidth) when the
sensitivity limits are not reached and is usually due to thermal noise, wrong PC
or component selection.Figure 4-17. Typical SNR Background
Versus RSSI on CEN_A Using DBPSK with Microchip Reference EKs
On a clean environment setup, the RX path helps to analyze the reception linearity
of the DUT (mainly transformer response on an isolated device) comparing the LQI average
for the same RSSI signal.Figure 4-18. Typical LQI Versus RSSI on
CEN_A Using DBPSK with Microchip Reference EKs
Detected errors on symbols or carriers is due to some impulsive or continuous carrier
noise. The common sources for these noises are:
Continuous Narrow Band Noise:
Usually associated with switching frequencies (or harmonics – mainly odd) of
AC/DC and DC/DC converters. Follow Microchip PLC HW guidelines.
Impulsive Noise: Usually
associated with other asynchronous transfers like SPI, I2C, radiated
coupling,commonly related to a poor PCB Layout or BOM. Follow Microchip PLC HW
guidelines.
Noise coming from mains.
According to the G3-PLC certification process, there are some limits that need to be
accomplished, depending on the modulation and white background noise, regarding Frame
Error Reception results with a maximum of 5% of errors:
Table 4-2. G3-PLC Performance SNR Limits
Statements for White Noise
