Microchip Technology PL360 User manual

PL360
PL360 Physical Calibration
Description
The PL360 is a programmable modem for narrow-band Power Line Communication (PLC), able to run
any PLC protocol in the frequency band below 500 kHz.
This device has been designed to comply with FCC, ARIB, KN60 and CENELEC EN50065 regulations
matching requirements of Internet of Things and Smart Energy applications. It supports state-of-the-art
narrow-band PLC standards such as ITU G.9903 (G3-PLC), ITU G.9904 (PRIME) as well as any other
narrow-band PLC protocols, at the same time being a future-proof platform able to support the evolution
of these standards.
The PL360 has been conceived to be driven by external Microchip host devices, thus providing an
additional level of flexibility on the host side. The Microchip host device loads the proper PLC-protocol
firmware before modem operation and controls the PL360 modem.
Implementation of firmware protocols over PL360 requires some values be calculated by calibration;
therefore, calibration process is essential in order to get the optimal PLC signal transmission behavior in
accordance with customer specifications.
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 1

Table of Contents
Description.......................................................................................................................1
1. Overview....................................................................................................................3
2. Physical Layer Capabilities........................................................................................4
2.1. Transmission Modes.................................................................................................................... 4
2.2. Impedance Detection................................................................................................................... 5
2.3. Equalization..................................................................................................................................7
3. How to Get Calibration Values...................................................................................8
4. How to Use Calibration Values................................................................................ 11
4.1. G3 Projects.................................................................................................................................11
4.2. PRIME Projects.......................................................................................................................... 12
5. Appendix A - Setup Description...............................................................................14
6. Appendix B - Requirements for phycalibrationtool.py..............................................15
7. Revision History.......................................................................................................16
7.1. Rev A - 10/2018......................................................................................................................... 16
The Microchip Web Site................................................................................................ 17
Customer Change Notification Service..........................................................................17
Customer Support......................................................................................................... 17
Microchip Devices Code Protection Feature................................................................. 17
Legal Notice...................................................................................................................18
Trademarks................................................................................................................... 18
Quality Management System Certified by DNV.............................................................19
Worldwide Sales and Service........................................................................................20
PL360
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 2

1. Overview
The objective of this user guide is to explain the transmission stage of the physical layer in G3 and
PRIME protocols and then show how to obtain more accurate calibration values in order to:
• Meet power injection requirements
• Meet signal quality requirements
• Compensate nonlinearities of the power supply, related to components tolerances and PCB layout
• Compensate nonlinearities of the coupling design, related to components tolerances and PCB
layout
To help in this calibration process of the PL360 PHY layer, Microchip provides the PHY Calibration Tool,
an open source application developed with Python®.
The Microchip G3 and PRIME stack implementations include default PHY layer configuration values
optimized for the Evaluation Kits. With the help of the PHY Calibration Tool it is possible to obtain the
configuration values for the customer´s hardware implementation.
PL360
Overview
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 3

2. Physical Layer Capabilities
The firmware implementation for G3 and PRIME protocols make use of the following concepts in
relationship with the transmission and reception stages:
• Transmission Modes
• Impedance Detection
• Equalization
2.1 Transmission Modes
Transmission modes are configurations applied to the PHY layer in order to improve the performance,
efficiency and spectrum ripple of the output driver according to the impedance detected in the line.
Depending on the detected impedance, two Transmission modes are defined:
• HI_STATE. Mode optimized for high impedance (Z > 20Ω)
• VLO_STATE. Mode optimized for very low impedance (Z < 10Ω)
Additionally, the PHY layer can modify the signal gain in a way that offers optimum results when
combined with the Transmission mode. This behavior is controlled by the PIB
PHY_PARAM_CFG_AUTODETECT_BRANCH. There are three operation modes:
• FIXED_STATE_FIXED_GAIN: Transmission mode and gain are fixed
• FIXED_STATE_VAR_GAIN: Transmission mode is fixed but the gain is managed by the Automatic
Gain Control (AGC) block to achieve signal level injection target
• AUTO_STATE_VAR_GAIN: Transmission mode and gain are managed dynamically to optimize the
output according to the line impedance and signal level injection target
Since each Transmission mode is optimized within an impedance range, it doesn't work properly in terms
of performance/efficiency when operating outside such range. Let’s suppose we have set a signal
injection objective of 110 dBuV for both HI and VLO modes. The following figures show the response of
forced modes in an impedance range from 0 to 50Ω.
PL360
Physical Layer Capabilities
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 4

Figures show the signal level when both Transmission mode and gain are fixed. In each mode, the
injected transmission signal is in its intended range, but out of such range, each mode is not achieving
the injection objectives. Also it can be seen that the response has a much more stable trend for
impedance above 20Ω, and below that, the transmission driver is more dependent on impedance
detected.
It is also possible to enable a configuration feature where transmission mode is fixed, but slight changes
in gain are allowed (PHY_ID_CFG_AUTODETECT_IMPEDANCE). This allowed variation in gain is not
enough to meet injection objective.
To meet objective in all impedance range (with some limitations in low impedance as explained above),
we have to rely on operation mode recommended where an Impedance Detection and Adaptation
algorithm is implemented in the Physical layer.
2.2 Impedance Detection
The following figure shows the response in AUTO_STATE_VAR_GAIN (1) operation mode, where the
system updates its response depending on the impedance detected in reception and following signal
level, compared to the fixed modes:
PL360
Physical Layer Capabilities
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 5

This adaptation is achieved by defining thresholds to switch from HI to VLO mode, and vice versa, which
determine the points where Transmission mode is changed.
These thresholds are defined such that the switch from HI to VLO is done in a lower impedance than the
switch from VLO to HI, obtaining a hysteresis window to avoid continuous switching between states which
will lead to a continuous change in signal injection, which is an undesirable scenario.
The following figure illustrates such thresholds and the hysteresis window they achieve:
As shown in the figure, the Auto response has been obtained sweeping from high to low impedance, this
is why the switch is done near the lower value of the hysteresis window (some point between 10 and
PL360
Physical Layer Capabilities
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 6

15Ω). If the sweep is done in the opposite way, from low to high impedance, the transition will be done
near the higher value of the hysteresis window, so the curve will follow the VLO curve inside the window
and then switch to HI curve just above 20Ω.
It is also seen that the Auto curve does not follow the trend of the forced ones exactly. This is because the
algorithm performs a fine tuning in each transmission according to the detected signal value, trying to
adjust more closely to the signal injection objectives.
2.3 Equalization
Usually the output transmission driver has a non-flat response inside the working band (ripple).
Depending on the difference between carriers, we may fall in a response out of the specification which
has to be corrected to meet the constraints.
The Physical layer is able to perform this equalization by means of signal pre-distortion, which
compensates the effect of the external driver, reducing the ripple, to give a final response closer to a flat
one.
Equalization has a tight relation with the Transmission modes seen in previous sections; in fact, each
Transmission mode defines a particular equalization. As configurations are different for each mode, the
response is also different, which requires different equalization.
An important aspect to take into account is that the objective of the equalization is to reduce ripple, giving
a flatter response, but keeping the average signal injection. Therefore, care must be taken in order to
reduce signal in some carriers and increase it in others, resulting in the same response after integrating
the signal level inside the operation band.
The following figure shows an example of equalization in the G3 Cenelec-A band:
The figure shows how the ripple is reduced after equalization, keeping the same signal average in band
(overlapped curves).
PL360
Physical Layer Capabilities
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 7

3. How to Get Calibration Values
Microchip provides a Python script named "phycalibrationtool.py" in order to get optimal calibration values
implied in the signal emission characterization which could affect to the ripple, amplitude and impedance
algorithm detection used by firmware on G3 and PRIME protocol implementations (Figure 3-3).
Requirements for phycalibrationtool.py can be found in 6. Appendix B - Requirements for
phycalibrationtool.py.
This application works over phy_tester_tool firmware, so this project example must be running on the
host microcontroller of PL360 board.
Along the test process, the PLC signal may be connected to different impedance loads; therefore, it is
strongly recommended to uncouple the PLC signal as far as possible from the mains power supply of the
device under test (Figure 3-1).
Figure 3-1. Calibration Setup
The Physical Calibration process implies the following steps:
• Initialization: set default equalization and gain calibration values used by PHY Calibration Tool
• Equalization: the objective is to get a flatter frequency response of the signal on the band in use; for
that a maximum ripple must be defined below the customer limits; as general rule, Microchip
recommends a margin of 0'5-1dB in order to handle the different impedance load of the
equalization performed
• Gain Calibration: the objective of gain calibration is to get the desired signal power in a range of
variable gain for AUTO GAIN mode. An initial gain must be defined and customer must decide
minimum and maximum values for AUTO GAIN mode. The minimum value could impact on the
performance of VLOW mode when emitting against high impedance if the system can't emit low
enough to maintain the signal on the PLC line. After modifying gain it is strongly recommended to
measure the ripple again in order to check if has been affected due to non-linearity when using a
high level of power
• Max RMS Level Process: the process gets the target RMS values for each Transmission mode
• Thresholds Process: the process calculates the threshold values in order to pass between
Transmission modes (high to VLOW and opposite)
PL360
How to Get Calibration Values
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 8

Figure 3-2. PHY Calibration Tool Main Window
Figure 3-3 shows the relationship between the steps and the firmware implementation, where:
• GAIN_C: Present Gain Value: a valid value between the maximum and minimum set on calibration
• RMS_C: RMS Power Calculated
• RMS_C_C: RMS Power Calculated Corrected used for threshold comparing in order to change the
TX mode
Figure 3-3. Firmware Transmission Path Implementation
PL360
How to Get Calibration Values
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 9

All the calibration steps require a similar setup to Figure 3-1 (more information about setup in section 6.
Appendix B - Requirements for phycalibrationtool.py)
"Equalization" and "Gain Calibration" steps must be run iteratively and require the user evaluation (ripple
and power measurements). On the other hand, the PHY Calibration Tool will automatically look for the
best values on "Max RMS Process" and "Thresholds Process" steps.
CAUTION
In each iteration, equalization must be reset in order to restore default values.
Figure 3-4. PHY Calibration Tool Workflow
INIT
Default
Equalization
-
Gain
POWER MEASURE
RIPPLE MEASURE
EQUALIZATION
•
Reset
Values
•
Get
optimized
Values
-
Insert
no
equalized
response.
-
Insert
maximum
ripple
required
.
-
Preview
preliminary
correction
.
•
Equalization
loss
is
automatically
compensated
.
SCRIPT
Calc MAX_
RMS
_VALUES
SCRIPT
Calc THRESHOLD
_
VALUES
Ripple
OK?
NO
YES
REPORT
GAIN
Adjust
GAIN INI
Power
OK?
YES
NO
PL360
How to Get Calibration Values
© 2018 Microchip Technology Inc. User Guide DS50002818A-page 10