Mixed-Mode Oscillator Control for Scalable Low-Power CDR
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Solution Overview
Problem
Conventional analog CDR circuits face challenges in scaling with process due to gate oxide current leakage, unstable control voltage, and high power consumption, while all-digital CDR solutions struggle with phase quantization error, area, and power consumption, as well as loop latency.
Innovation Solution
A mixed mode controlled oscillator circuit is developed, incorporating a charge pump and digital loop filter to control the oscillator's output frequency using both current and digital code signals, reducing area and power consumption by combining analog and digital control paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional analog CDR circuits are used, then clock data recovery function is achieved, but gate oxide current leakage causes unstable control voltage and poor scalability with process
Solution Approach 1:
The CDR circuit is segmented into two independent control paths: an analog path using a charge pump to generate current signals for fine frequency adjustment, and a digital path using a digital loop filter to generate digital control codes for coarse frequency adjustment. This segmentation allows each path to operate independently, avoiding the gate oxide leakage issue in analog devices while maintaining frequency control stability.
Solution Approach 2:
A dual-controlled oscillator is introduced as an intermediary device that accepts both analog current signals from the charge pump and digital control codes from the digital loop filter. This intermediary component integrates both control mechanisms, enabling the system to achieve stable frequency control without relying solely on vulnerable analog devices.
2Adaptability or versatility
If all-digital CDR solutions are used, then scalability with process is improved, but phase quantization error and loop latency increase
Solution Approach 1:
Different quality levels are applied to different parts of the control system: the digital loop filter provides coarse frequency adjustment with lower precision requirements, while the charge pump provides fine frequency adjustment with higher precision requirements. This local quality differentiation allows the system to achieve overall high precision without requiring all components to be high-precision digital devices.
3Adaptability or versatility
If all-digital CDR solutions are used, then scalability is improved, but area and power consumption increase due to phase interpolator requirements
Solution Approach 1:
The complex phase interpolator circuit is extracted and replaced with simpler components: a digital loop filter that generates digital control codes and a charge pump that generates current signals. This extraction eliminates the need for area-intensive phase interpolator circuits while maintaining the ability to achieve precise frequency control through the combination of digital and analog paths.
4Adaptability or versatility
If all-digital CDR solutions are used, then scalability is improved, but loop latency increases
Solution Approach 1:
The system dynamically switches between digital and analog control paths based on the required adjustment range. The digital loop filter handles coarse adjustments that can be performed quickly in the digital domain, while the charge pump handles fine adjustments with its inherently fast analog response. This dynamic allocation of control tasks minimizes overall loop latency.
Data Source
AI summary
A circuit for controlling a mixed mode controlled oscillator. The circuit comprises a charge pump, and a digital loop filter. The charge pump is coupled to the mixed mode controlled oscillator. The charge pump receives an up/down signal and sends a current signal to the mixed mode controlled oscillator. The digital loop filter receives the up/down signal and generates a digital code signal to the mixed mode controlled oscillator. An output frequency of the mixed mode controlled oscillator is controlled by the current signal and the digital code signal.