Reverse-Channel Clock Recovery for Crystal-Free Bidirectional Links
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Solution Overview
Problem
Bi-directional serial data links require accurate timing references (clocks) at both ends, which increases component count and cost, and can be unreliable due to temperature variations, especially in systems like surround view camera systems for vehicles.
Innovation Solution
A bidirectional serial data link system where a remote device establishes a reference clock without using a crystal oscillator, utilizing a clock recovery circuit that includes a phase lock loop (PLL) and a voltage-controlled oscillator (VCO) to lock onto a clock reference data embedded in the serialized data from the far-side device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If crystal oscillators are used at both ends of the bidirectional serial data link to provide accurate timing references, then clock accuracy is improved, but component count and system cost increase
Solution Approach 1:
The patent extracts the crystal oscillator from the remote device and relocates it to the far-side device only. The remote device obtains timing reference by recovering the clock signal embedded in the serialized data transmitted over the reverse channel, eliminating the need for a crystal oscillator at the remote end while maintaining clock accuracy.
Solution Approach 2:
The reverse channel, originally designed for lower bandwidth communication, is utilized to embed and transmit clock reference data. This multi-functional use of the reverse channel allows it to serve both data communication and clock distribution purposes, reducing the need for separate dedicated clock paths and components.
2Measurement precision
If crystal oscillators are used at both ends of the bidirectional serial data link, then timing reference accuracy is improved, but system cost increases
Solution Approach 1:
The patent removes the crystal oscillator component from the remote device bill of materials and relocates its function to the far-side device. The remote device achieves timing reference accuracy through clock recovery from the embedded clock signal in the serialized data, reducing overall system component cost.
Solution Approach 2:
Instead of using a physical crystal oscillator at the remote device, the patent creates a functional copy of the clock signal by embedding it in the serialized data stream. The remote device reconstructs the timing reference from this embedded signal, achieving the same timing accuracy without the physical oscillator component.
3Reliability
If crystal oscillators are installed at remote devices, then timing reference is provided, but reliability decreases under extreme temperature variations
Solution Approach 1:
The patent extracts the temperature-sensitive crystal oscillator from the remote device environment and places it only at the far-side device, which is typically in a more controlled environment. The remote device obtains its timing reference from the transmitted clock signal, isolating it from temperature variations and improving reliability in harsh environments.
Solution Approach 2:
The embedded clock signal in the serialized data acts as an intermediary, transferring the stable timing reference from the far-side device to the remote device without requiring the remote device to generate its own clock. This intermediary transmission protects the remote device from temperature-induced frequency drift.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces the component count and cost by eliminating the need for crystal oscillators at remote devices, while maintaining accurate clock synchronization, thus enhancing reliability even under extreme temperature variations.
Implementation Method 1
a phase lock loop including a first detector configured to receive the serial data stream and to detect phase and frequency
Implementation Method 2
a voltage controlled oscillator configured to selectively communicate with an output of the first detector and to output a clock signal
Implementation Method 3
a second detector configured to receive the serial data stream and to detect phase, the second detector including a Hogge phase detector
Data Source
AI summary
A clock recovery circuit includes a clock detector configured to receive a serial data stream from a remote device over a reverse channel, wherein the serial data stream includes clock reference data, reverse channel data, or a combination of the clock reference data and the reverse channel data, and the clock detector configured to output a clock detect signal in response to detecting the clock reference data in the serial data stream; a phase lock loop including a first detector configured to receive the serial data stream and to detect phase and frequency; and a controller configured to receive the clock detect signal and to selectively enable the first detector based on the clock detect signal.