Molecular Clock Even Harmonic Suppression via N-path Filter
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Solution Overview
Problem
Electronic devices require highly stable, portable, and energy-efficient reference signal sources, especially in environments where GPS signals are unavailable, and existing mechanical oscillators suffer from long-term frequency drift due to environmental disturbances.
Innovation Solution
A molecular clock system incorporating a waveguide gas cell, a voltage-controlled oscillator, a transmitter, a receiver with a filter circuit including a N-path notch filter to eliminate even harmonics, and a lock-in detector for feedback control, which stabilizes the clock signal by locking onto rotational energy level transitions of gaseous molecules like carbonyl sulfide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a molecular clock system is designed to achieve high frequency stability and portability, then it can operate independently of GPS signals in environments like underwater sensors, but the system requires complex filtering circuits to eliminate even harmonics which increases device complexity
Solution Approach 1:
The patent extracts and removes the harmful even harmonic components from the signal path using a dedicated filter circuit. By specifically targeting and eliminating only the even harmonics (2nd, 4th, 6th order) while preserving the fundamental and odd harmonic signals, the system achieves the required frequency stability without needing to redesign the entire clock architecture.
Solution Approach 2:
The filter circuit acts as an intermediary component between the frequency synthesizer and the reference signal output. This mediator selectively passes desired frequency components while blocking harmful even harmonics, enabling the molecular clock to achieve high reliability without directly modifying the core oscillation mechanism.
2Weight of moving object
If mechanical oscillators are used in portable equipment, then the device can be compact and portable, but they suffer from long-term frequency drift due to environmental disturbances such as temperature and vibration
Solution Approach 1:
The patent replaces the mechanical oscillator system with an electronic frequency synthesizer based on a phase-locked loop (PLL) architecture. This electronic substitution eliminates the mechanical moving parts that are susceptible to environmental disturbances, while maintaining portability. The PLL-based synthesizer locks to a stable reference frequency, providing long-term stability without mechanical components.
Solution Approach 2:
The system uses a voltage-controlled oscillator (VCO) whose frequency can be dynamically adjusted through voltage control to maintain locking accuracy. By changing the control voltage parameter in response to detected frequency errors, the system compensates for environmental variations and maintains stable operation in portable conditions.
3Power
If the baseband gain GBB is increased to improve signal processing capability, then better signal detection is achieved, but the presence of even-order harmonics limits the maximum achievable gain
Solution Approach 1:
The patent converts the harmful effect of even-order harmonics into a beneficial filtering opportunity. By deliberately designing the filter circuit to target and eliminate these even harmonics, the system transforms what was previously a limiting factor into an enabler for higher baseband gain. The filtered signal path can then accommodate higher gain settings without being corrupted by harmonic distortion.
Solution Approach 2:
The filter circuit is positioned in the signal path before the baseband amplification stage, performing preliminary removal of even harmonics. This preliminary action prevents harmonic distortion from being amplified along with the desired signal, enabling the subsequent high-gain baseband processing to operate on clean signal content.
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
The molecular clock achieves frequency stability comparable to chip-scale atomic clocks, with improved long-term stability and energy efficiency, reducing the impact of environmental disturbances and enabling compact, real-time operation.
Implementation Method 1
a filter circuit configured to filter out even harmonic components from the received signal
Implementation Method 2
a lock-in detector to generate an error signal indicating an offset between the first frequency and the second frequency, wherein the error signal is fed back to control generation of the VCO clock signal
Implementation Method 3
a voltage-controlled oscillator (VCO) to generate a clock signal
Implementation Method 4
a waveguide gas cell containing gas molecules having a rotational spectral line with a first frequency
Data Source
AI summary
In some embodiments, a molecular clock includes a waveguide gas cell containing gas molecules having a rotational spectral line with a first frequency a voltage-controlled oscillator (VCO) to generate a clock signal, a transmitter referenced to the clock signal to generate a probing signal for transmission through the waveguide gas cell, and a receiver to receive the probing signal transmitted through the waveguide gas cell and interacting with gas molecules. The receiver can include a filter circuit configured to filter out even harmonic components from the received signal and can further include a lock-in detector to generate an error signal indicating an offset between the first frequency and the second frequency. The error signal is fed back to control generation of the VCO clock signal.