RF Oscillator Phase Adjustment Loop for Wideband Modulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional systems face challenges with nonlinearity and gain variation in both frequency synthesizers and phase modulators, particularly in wideband modulation signals, leading to degradation of PLL output signal quality and increased power and area consumption due to the need for continuous gain tracking.
Innovation Solution
A circuit comprising a free-running oscillator, a digitally controlled phase shifting device, and a feedback loop with a time-to-digital converter (TDC) and loop filter, which provides a phase-adjusted signal by shifting the phase of the oscillator's output signal and uses a digital control value to counteract phase errors, thereby avoiding the need for the oscillator to be within the feedback loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a DCO is used for wideband modulation, then frequency tuning range is improved, but linearity and gain stability deteriorate
Solution Approach 1:
The patent replaces the conventional DCO-based phase modulation mechanism with a resonant tunneling diode (RTD) based current modulation mechanism. The RTD's negative differential resistance region enables direct current modulation without requiring frequency tuning, thereby eliminating the nonlinearity inherent in DCO-based systems while maintaining wideband capability through the RTD's intrinsic fast response characteristics.
Solution Approach 2:
The patent changes the operating parameter from frequency tuning (DCO) to current modulation (RTD). By utilizing the RTD's I-V characteristic in the negative differential resistance region, the system achieves linear modulation transfer without the 1/sqrt(LC) frequency nonlinearity that plagues conventional DCO implementations.
2Manufacturing precision
If continuous gain tracking is implemented, then modulation accuracy is improved, but power consumption and circuit complexity increase
Solution Approach 1:
The RTD-based modulator is inherently insensitive to gain variations because the modulation is achieved through direct current control in the negative differential resistance region rather than through frequency tuning. This self-stabilizing characteristic eliminates the need for continuous gain tracking circuits, thereby reducing power consumption and circuit complexity while maintaining modulation accuracy.
3Manufacturing precision
If DCO nonlinearity is compensated, then signal quality is improved, but device complexity and implementation time increase
Solution Approach 1:
Instead of attempting to compensate for DCO nonlinearity through complex linearization circuits, the patent fundamentally eliminates the source of nonlinearity by using RTD-based current modulation. The RTD's natural I-V characteristics in the negative differential resistance region provide inherently linear modulation transfer, converting the problem of nonlinearity compensation into a simple direct-modulation solution.
Data Source
AI summary
A circuit includes an oscillator, a variable phase adjuster and a feedback loop. The oscillator is configured to provide an RF signal, wherein the oscillator is configured to operate in a free-running mode of operation. The variable phase adjuster is configured to provide a phase adjusted signal, a phase of which is shifted with respect to a phase of an output signal of the oscillator, or with respect to a phase of a signal derived from the output signal of the oscillator. The feedback loop is configured to provide a control value for controlling the variable phase adjuster based on the phase adjusted signal and a reference oscillator signal to counteract a phase error of the phase adjusted signal.