Ring Oscillator Harmonic Extraction for Terahertz Signal Output
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Solution Overview
Problem
Implementing a fully integrated terahertz camera based on silicon technology is challenging due to the high frequency and low energy of terahertz signals, and existing imagers struggle to capture image depth and improve image quality.
Innovation Solution
A frequency oscillator circuit comprising a ring oscillator with N inverters coupled in series, where N is an odd integer, and filters are used to extract the Nth harmonic frequency, which is then combined to generate a terahertz signal in the range of 300 GHz to 3 THz, overcoming the limitations of MOS transistor frequency and enhancing signal amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a ring oscillator with N inverters is used to generate terahertz signals, then the frequency range of 300 GHz to 3 THz can be achieved, but the signal amplitude remains low due to MOS transistor frequency limitations
Solution Approach 1:
Multiple ring oscillators are combined in parallel, with their output signals summed together at a common node. This merging of multiple oscillating signals increases the overall signal amplitude while maintaining the high frequency capability of individual oscillators, thereby resolving the contradiction between achieving terahertz frequencies and maintaining sufficient signal amplitude.
2Speed
If filters are added to extract the Nth harmonic frequency, then the terahertz signal can be generated, but the device complexity increases
Solution Approach 1:
The frequency multiplication function is segmented across multiple identical ring oscillator units rather than requiring a single complex frequency synthesizer. Each unit generates the base frequency, and the Nth harmonic extraction is distributed across multiple parallel paths, simplifying the overall design while achieving the desired terahertz frequency.
Solution Approach 2:
The same ring oscillator circuit structure serves multiple functions: generating the fundamental frequency, producing harmonic frequencies, and providing signals that are summed to increase amplitude. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby reducing overall device complexity.
3Power
If multiple ring oscillators are combined to increase signal amplitude, then the power is improved, but the device complexity increases
Solution Approach 1:
Instead of designing a single complex high-power oscillator, multiple copies of a simple ring oscillator circuit are created and operated in parallel. Each copy is identical and relatively simple, but their combined output provides the necessary signal amplitude, trading numerical multiplication of simple units for the achievement of high power output.
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 allows for the generation of high-frequency terahertz signals within the terahertz range, improving the capability to capture detailed images and potentially capturing image depth, while overcoming the limitations of MOS transistor frequency limitations.
Implementation Method 1
The oscillating signal is generated at the output of each of the inverters. The oscillating signals at the output of at least two of the inverters are filtered to extract the Nth harmonic
Implementation Method 2
A first filter is coupled between an output node of a first of the inverters and an output line of the frequency oscillator. A second filter is coupled between an output node of a second of the inverters and the output line of the frequency oscillator. The first and second filters are each adapted to filter out at least the fundamental frequency component present at the output nodes of the first and second inverters.
Implementation Method 3
at least one line connecting a pair of inverters of the first ring oscillator is positioned to be electro-magnetically coupled to at least one line connecting a pair of inverters of the second ring oscillator
Data Source
AI summary
A frequency oscillator includes a ring oscillator having N inverters coupled in series, where N is an odd integer equal to three or more. A first filter is coupled between an output node of a first of the inverters and an output line of the frequency oscillator. A second filter is coupled between an output node of a second of the inverters and the output line of the frequency oscillator.