Reverse-Channel Clock Recovery for Crystal-Free Serial Links
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Solution Overview
Problem
Bidirectional serial data links require crystal oscillators at both ends, increasing component count and cost, and are unreliable due to temperature variations, especially in applications like surround view camera systems where multiple remote devices need accurate timing references.
Innovation Solution
A clock recovery circuit at the remote device establishes a reference clock without using a crystal oscillator by detecting a clock reference signal embedded in serialized data and locking a phase-locked loop, allowing the voltage-controlled oscillator to generate the clock in closed loop mode after initial open loop operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If crystal oscillators are used at both ends of the bidirectional serial data link, then accurate timing reference is maintained, but component count and system cost increase significantly
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 from the serialized data transmitted over the reverse channel, eliminating the need for a crystal oscillator at the remote end while maintaining timing accuracy.
Solution Approach 2:
The reverse channel, originally designed for lower bandwidth communication, is utilized to transmit the clock reference signal. This multi-functional use of the reverse channel allows it to serve both data transmission and clock distribution purposes, reducing the need for separate dedicated clock paths and components at the remote device.
2Measurement precision
If crystal oscillators are installed at remote devices, then timing accuracy is maintained, but reliability decreases due to temperature variations
Solution Approach 1:
The patent removes the temperature-sensitive crystal oscillator from the remote device environment. By centralizing the crystal oscillator at the far side device (which has more stable operating conditions) and transmitting the clock signal through the serial data link, the system eliminates the reliability issue caused by temperature variations at remote locations.
Solution Approach 2:
The serialized data signal acts as an intermediary carrier to transmit the clock reference from the far side device to the remote device. This intermediary transmission method allows the remote device to obtain a stable clock reference without having its own temperature-sensitive oscillator, as the clock signal travels through the controlled environment of the far side device.
3Measurement precision
If multiple crystal oscillators are used in surround view camera systems, then each remote camera maintains accurate timing, but overall system cost increases
Solution Approach 1:
The patent extracts the expensive crystal oscillator component from each remote camera and consolidates it to a single location at the far side device. This reduction in component quantity directly lowers the bill of materials cost while maintaining timing accuracy through clock signal recovery in the serialized data stream.
Solution Approach 2:
The patent merges the clock generation function from multiple distributed crystal oscillators into a single centralized clock source at the far side device. This consolidated approach reduces component count and cost while the clock signal is distributed to all remote devices through the serial data link, achieving the same timing synchronization effect with fewer components.
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 component costs and improves reliability by eliminating the need for crystal oscillators at remote devices, maintaining accurate timing references across varying temperatures while enabling efficient data transmission in both high and low bandwidth directions.
Implementation Method 1
a phase-locked loop that detects phase and frequency of the clock reference signal to generate a timing reference at the remote device
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.