Functional Description
Microsemi Proprietary and Confidential UG0677 User Guide Revision 9.0 12
3.1.1.9 Receiver Calibration
The PolarFire XCVR receivers include both analog and digital blocks that require calibration to
compensate for process, voltage, and temperature (PVT) variations in conjunction with signal integrity.
The embedded calibration block of PolarFire transceiver performs calibration operations that optimize
the performance of the transceiver interconnection. It includes an adaptive deserializer calibration
algorithm to correct for lossy channels.
Libero selects CTLE only and CTLE/DFE modes based on the system data rate and channel loss needs.
The pre-determined settings provide the starting point for the design. These settings are configured to
the appropriate calibration requirements based on the targeted requirements. Three types of calibrations
are carried out within the Rx:
• CTLE DC-offset
• CTLE Frequency Response
• DFE
3.1.1.9.1 CTLE DC-offset Calibration
Process, voltage, and temperature (PVT) variations result in a DC-offset of the receiver front-end
amplifiers, that is, the output is different from zero when the input is zero. This limits the sensitivity of the
receiver and therefore the signal-to-noise ratio (SNR). It also limits the performance of the other
calibration mechanisms.
The CTLE DC-offset calibration circuitry calibrates the DC-offset by zeroing the input and adding an
offset. This offset is dynamically determined by a binary search in response to the logic output of the
amplifier.
3.1.1.9.2 CTLE Frequency Response Calibration
The CTLE frequency response can be set to a few discrete values, therefore calibration depends on
searching for the settings that result in the largest eye area.
CTLE DC_offset and CTLE Frequency Response calibration together make up the CTLE solution. For
the most lossy and disruptive channels, many or all CTLE settings combinations can result in a zero eye-
opening area. In these scenarios, DFE can sometimes allow for a non-zero area, which would otherwise
be impossible with CTLE alone.
3.1.1.9.3 DFE Calibration
DFE calibration is carried out by an embedded sequence function, which is optimized to avoid local
minima, achieve predictable results, allow for low area, and operate at high clock speeds. It adjusts the
feedback coefficients in response to the eye-area. The sequence of the function is used to determine the
width, height, and center of the eye opening. DFE Calibration is carried out by a algorithm that adjusts
the feedback coefficients (from H1 to H5) by trial-and-error in response to the eye-area of the
eye_monitor. The algorithm operates on one dimension (a single coefficient) at a time. It takes a step of
size 1 in the positive direction and then the negative direction that is H1+1 and H1-1. If the area improves
on either step, it continues to take another step in the same direction. If both directions yield a lower area,
it continues to the next coefficient with the same step size. After failing to improve the area on all
coefficients, it increases the step size and continue. If the area is improved, the step size immediately
reduces to 1. See the AC468: PolarFire FPGA Transceiver Decision Feedback Equalization Application
Note for more information.
Dependent on the specific design targets chosen through Libero, the design can be configured in one of
two modes that require calibration of the receiver.
In CTLE only mode, CTLE solution is executed to optimize gain/frequency settings using CTLE
Frequency Response and DC Offset calibration.
In CTLE/DFE mode, CTLE calibration is first run to optimize gain/frequency settings using CTLE
Frequency Response and DC Offset calibration. DFE calibration is then run for centering and
coefficients.
DFE is optionally programmed to be used in several operations. Full DFE calibration autonomously
calibrates to the best found DFE coefficients for optimized data eye centering. These are controlled by
Libero specified options.
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