# A fully-digital semi-rotational frequency detection algorithm for bang-bang CDRs

## TL;DR

This paper introduces a fully digital semi-rotational frequency detection algorithm for bang-bang CDRs that enables reference-less, high-speed data recovery with online VCO calibration, implemented in a 65nm CMOS transceiver.

## Contribution

It proposes a novel SRFD algorithm for bang-bang CDRs that simplifies implementation and improves frequency acquisition without external references.

## Key findings

- Successfully recovers input phase at 10 Gbps
- Implemented in a 65nm CMOS process
- Enables online VCO calibration for temperature and voltage variations

## Abstract

This work presents a new frequency acquisition method using semi-rotational frequency detection (SRFD) algorithm for a reference-less clock and data recovery (CDR) in a serial-link receiver. The proposed SRFD algorithm classifies the bang-bang phase detector(BBPD) outputs to estimate the current phase state, and detects the frequency mismatch between the input data and the sampling clock. The VCO-track path in a digital loop filter (DLF) enables online calibration of a drifted frequency of VCO caused by temperature or voltage variation after a frequency acquisition. The proposed algorithm can be implemented as a digitally-synthesized circuit, lowering design efforts for referenceless CDRs. A 10 Gbps transceiver IC with the proposed algorithm, fabricated in a 65nm CMOS process, demonstrates successful recovery of the input phase without any reference clock.

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Source: https://tomesphere.com/paper/1905.00273