3.2.2 Rx CTLE

CTLE at the receiver end is a typical equalization technique for equalizing the incoming signal to a flat response. CTLE is used to reduce the low-frequency component of the signal while boosting the high-frequency component. The receiver equalization settings are a function of the cut-off frequency and the amplitude gain across data rates. The equalizer circuitry can be tuned to compensate for the signal distortion due to the high frequency reduction of the physical channel of the PCB and interconnect.

For example, an under-equalized channel cannot adequately open the eye, whereas over-equalization can produce a channel with high jitter.

Correct equalization has optimal eye opening with low noise and low jitter. Rx insertion loss default settings sets the CTLE. AC483: PolarFire FPGA Transceiver Signal Integrity Application Note lists the combination of settings that help the user to find the best response to the incoming signal based on data rate “buckets”. Within each bucket, there are optimized settings based on gain and peaking. When using DFE designs, users must not alter the predefined values of CTLE. These values are optimized to work in conjunction with the DFE configuration based on Rx insertion defaults as listed in following table.