VCO Noise Bypass Circuit for Phase Noise Reduction
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Solution Overview
Problem
Voltage controlled oscillators (VCOs) face challenges in reducing noise, particularly phase noise, due to thermal noise and other factors, which affects their performance in applications like communications and radar systems.
Innovation Solution
The implementation of a noise by-pass circuit in the VCO, connected in parallel with the LC tank circuit and oscillator core, forms a low-impedance path at approximately twice the oscillator frequency, reducing noise contribution and immunizing the oscillator core from external noise. This circuit can include a series resonance tuned with a capacitor and inductor or a transmission line, with adjustable components to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a noise by-pass circuit is added to reduce phase noise, then phase noise is reduced, but device complexity increases
Solution Approach 1:
A noise by-pass circuit is introduced as an intermediary element connected in parallel with the LC tank circuit. This by-pass circuit provides a dedicated low-impedance path for noise currents at twice the oscillator frequency, allowing noise to be shunted away from the oscillator core while maintaining the primary oscillation function. The by-pass circuit acts as a mediator that separates noise suppression from the main oscillation path.
Solution Approach 2:
The noise by-pass circuit is designed with specific impedance characteristics that change with frequency. By tuning the by-pass circuit to present low impedance at twice the oscillator frequency (2fosc) while maintaining high impedance at the fundamental frequency (fosc), the circuit selectively suppresses noise without affecting the main oscillation. This parameter-based separation allows noise reduction while preserving oscillator performance.
2Object-generated harmful factors
If a low-impedance path is created at twice the oscillator frequency, then noise contribution from cross-coupled devices is reduced, but device complexity increases
Solution Approach 1:
The cross-coupled semiconductor devices inherently generate noise at twice the oscillator frequency due to their switching nature. Instead of attempting to eliminate this noise source, the invention converts this harmful effect into a manageable characteristic by designing the by-pass circuit to specifically target and shunt this frequency component. The noise energy generated by the cross-coupled devices is redirected through the low-impedance by-pass path to ground, transforming a harmful byproduct into a controlled element.
3Reliability
If the noise by-pass circuit is tuned to resonate at approximately twice the oscillator frequency, then phase noise is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The noise by-pass circuit incorporates variable or tunable components that allow the resonance frequency to be dynamically adjusted during manufacturing and operation. This dynamic tuning capability enables precise alignment of the by-pass circuit's resonance frequency with twice the oscillator frequency, compensating for component tolerances and ensuring optimal noise suppression across different operating conditions and manufacturing variations.
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 solution significantly reduces phase noise, improving the stability and efficiency of the VCO output, as demonstrated by simulations showing a substantial decrease in noise levels, enhancing the reliability and quality of data transfer in communications and radar applications.
Implementation Method 1
the noise by-pass circuit comprises a series resonance tuned to resonate at approximately twice the oscillator frequency
Implementation Method 2
forms a low-impedance path at a frequency approximately twice the oscillator frequency
Data Source
AI summary
A voltage controlled oscillator (VCO), a method of designing a voltage controlled oscillator, and a design structure comprising a semiconductor substrate including a voltage controlled oscillator are disclosed. In one embodiment, the VCO comprises an LC tank circuit for generating an oscillator output at an oscillator frequency, and an oscillator core including cross-coupled semiconductor devices to provide feedback to the tank circuit. The VCO further comprises a supply node, a tail node, and a noise by-pass circuit connected to the supply and tail nodes, in parallel with the tank circuit and the oscillator core. The by-pass circuit forms a low-impedance path at a frequency approximately twice the oscillator frequency to at least partially immunize the oscillator core from external noise and to reduce noise contribution from the cross-coupled semiconductor devices.