Synchronized Oscillator PLL Circuit for Harmonic Frequency Control
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Solution Overview
Problem
Current frequency control systems in scanning probe microscopy, particularly digital PLLs, face limitations in running cantilever excitation and detection at harmonic frequencies, are costly, and struggle with constant frequency changes, making it difficult to provide fixed offsets from fluctuating base frequencies or generate pure sine waves.
Innovation Solution
A frequency measuring and control apparatus with multiple synchronized oscillators integrated into a programmable logic device, utilizing a single system clock for exact phase synchronization and eliminating clock jitter, allowing for precise control and synchronization of excitation and detection signals across multiple channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital PLL circuits are used for non-contact AFM, then stability and accuracy in frequency detection are improved, but it is not possible to run cantilever excitation and PLL detection at harmonic frequencies
Solution Approach 1:
The system is divided into multiple independent DDS channels, each capable of operating at different frequencies. The PLL detector channel and excitation channel are segmented as separate functional units within the same integrated circuit, allowing them to operate independently at fundamental or harmonic frequencies simultaneously.
Solution Approach 2:
The integrated circuit provides universal functionality by incorporating multiple DDS channels that can serve different purposes - one channel for PLL detection and others for excitation. This multi-functional design allows the same hardware platform to handle both detection and excitation at various frequency relationships including harmonics.
2Difficulty of detecting and measuring
If additional lock-in amplifiers are used to analyze signals in parallel, then detection capability is improved, but system cost increases considerably
Solution Approach 1:
Multiple signal analysis functions are merged into a single integrated circuit. The DDS channels generate excitation signals while the PLL detector performs frequency detection, all within one unified hardware platform. This consolidation eliminates the need for separate external lock-in amplifiers and reduces overall system cost.
Solution Approach 2:
The integrated circuit provides universal signal processing capability, handling both excitation generation and detection functions. This multi-functional approach replaces multiple separate instruments with a single device, reducing cost while maintaining detection capability.
3Ease of operation
If separate reference oscillator and excitation signal are used, then frequency control is achieved, but synchronization between excitation and detection channels is difficult
Solution Approach 1:
Multiple oscillator channels are merged into a single integrated circuit sharing a common clock source. This unified architecture ensures that all DDS channels and the PLL detector are automatically synchronized to the same reference frequency, eliminating synchronization issues that arise from using separate external oscillators.
Solution Approach 2:
A common internal clock source acts as an intermediary that synchronizes all frequency-generating channels. This central timing reference ensures that excitation and detection channels maintain precise phase relationships, with the clock serving as the mediating element that coordinates all operations.
Data Source
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AI summary
A frequency measuring and control apparatus includes a plurality of synchronized oscillators integrated in parallel into one programmable logic device.