PLL Circuit With Mixed-Voltage Loop Filter for Wide Vctrl Range
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Solution Overview
Problem
Existing PLL circuits with low KVCO face challenges in achieving a wide frequency adjusting range due to limited available Vctrl range, which is insufficient for GHz-level output frequencies, leading to area inefficiencies and increased jitter.
Innovation Solution
The design incorporates a phase frequency detector, charge pump, active loop filter, and feedback divider, where the charge pump operates at a lower voltage and higher speed using core devices, while the active loop filter operates at a higher voltage, enabling a wider Vctrl range and reducing the gain value of the controlled oscillator, thus enhancing frequency adjusting range and reducing jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low KVCO is used to minimize jitter and reduce loop filter capacitor size, then jitter performance and area are improved, but frequency adjusting range becomes limited due to small available Vctrl range
Solution Approach 1:
The charge pump is segmented into core devices operating at low voltage (1.2V) for jitter reduction and I/O devices operating at high voltage (3.3V) for extended control voltage range. This segmentation allows the system to simultaneously achieve low jitter performance and wide frequency adjusting range by having different voltage domains perform different functions.
Solution Approach 2:
Different parts of the charge pump are assigned different operating voltages based on their functional requirements. The core devices use low voltage to minimize noise and jitter, while the I/O devices use high voltage to provide sufficient control voltage swing for GHz-level frequency adjustment. This local quality differentiation resolves the contradiction between jitter performance and frequency range.
2Object-affected harmful factors
If low operating voltage is used in charge pump to reduce jitter, then jitter is minimized, but frequency adjusting range is insufficient for GHz-level output
Solution Approach 1:
The charge pump is divided into core devices operating at 1.2V to minimize jitter and I/O devices operating at 3.3V to enable GHz-level frequency output. This segmentation allows the system to simultaneously achieve low jitter and high frequency capability by having different voltage domains perform different functions.
Solution Approach 2:
Different parts of the charge pump are assigned different operating voltages based on their functional requirements. The core devices use low voltage to minimize noise and jitter, while the I/O devices use high voltage to provide sufficient control voltage swing for GHz-level frequency adjustment. This local quality differentiation resolves the contradiction between jitter performance and frequency range.
3Adaptability or versatility
If higher operating voltage is used in active loop filter, then wider Vctrl range is achieved, but device complexity increases due to mixed voltage domains
Solution Approach 1:
The charge pump is segmented into core devices operating at low voltage and I/O devices operating at high voltage. This segmentation clearly defines the boundaries between different voltage domains, making the mixed voltage design manageable and systematic rather than chaotic, thus reducing the perceived complexity.
Solution Approach 2:
Different parts of the charge pump are assigned different operating voltages based on their functional requirements. This systematic assignment of local voltage qualities creates a structured mixed voltage domain design that is easier to manage and implement compared to a uniform voltage approach that would require additional voltage conversion components.
Data Source
AI summary
A phase lock loop circuit is provided. A phase frequency detector detects a phase difference between a feedback signal and a reference signal, and generates a phase error signal in response to the detected phase difference. A charge pump consists of at least one core device and outputs a current signal based on the phase error signal. An active loop filter receives and transfers the current signal into a control signal. Operating voltage of the active loop filter is higher than operating voltage of the charge pump. A controlled oscillator receives the control signal and generates an output signal in response to the control signal. A feedback divider receives the output signal to generate the feedback signal.