VCO CTAT Current Compensation for Low-Band Frequency Drift
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Solution Overview
Problem
Wide band PLLs suffer from significant frequency drift issues due to temperature variations, which are not effectively addressed by existing temperature compensation methods, limiting the frequency correction range, especially at lower frequency bands where signal gain is low.
Innovation Solution
A circuit and method that introduce a conversely proportional to absolute temperature (CTAT) response in the output current of a voltage to current converter (V2I) connected to a ring oscillator (RO), providing a fixed offset current to the V2I resistor node to mirror the output current and reduce temperature-induced frequency drift at lower frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature compensation circuits (PTAT/CTAT) are used to correct VCO frequency drift, then frequency stability is improved, but the frequency correction range is limited especially at lower frequency bands
Solution Approach 1:
The patent implements dynamic temperature compensation by selectively activating different compensation circuits (first CTAT circuit for higher frequency bands, second CTAT circuit for lower frequency bands) based on the operating frequency range. This dynamic adaptation allows the system to maintain both frequency stability and adequate correction range across the entire operating spectrum.
Solution Approach 2:
The temperature compensation function is segmented into multiple independent CTAT circuits, each optimized for specific frequency bands. The first CTAT circuit handles higher frequency bands while the second CTAT circuit handles lower frequency bands, allowing each segment to be independently tuned for optimal performance in its designated range.
2Use of energy by moving object
If control voltage range is reduced due to supply scaling at lower technology nodes, then power consumption is reduced, but the ability to correct frequency drift is compromised
Solution Approach 1:
The patent replaces the traditional voltage-based frequency drift correction mechanism with current-based CTAT compensation circuits. By using current mirrors and CTAT current sources, the system achieves frequency drift correction through current modulation rather than relying solely on control voltage adjustments, thereby maintaining correction capability despite reduced voltage headroom.
Solution Approach 2:
The invention changes the compensation parameter from voltage-dependent to current-dependent by implementing CTAT current sources that directly modulate the VCO tank current. This parameter transformation allows the compensation mechanism to remain effective even when the control voltage range is constrained by supply scaling.
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 approach effectively reduces temperature-induced frequency drift, extending the fine-tune frequency correction range without affecting loop dynamics, thereby improving communication signal quality and reducing interference in adjacent frequency bands.
Implementation Method 1
A temperature coefficient for the ICCO current is induced in an opposite direction to the temperature coefficient of the CCO
Implementation Method 2
introducing a conversely proportional to absolute temperature (CTAT) response in a V2I output current to a ring oscillator (RO)
Data Source
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AI summary
A circuit for reducing a temperature-induced frequency drift in a voltage to current (V2I) converter based voltage-controlled oscillator (VCO) for at least one wide band phase-locked loop (PLL), the circuit includes a V2I resistor node of the V2I converter, the V2I resistor node being at one end of a resistor, the VCO, and a current controlled oscillator (CCO), and the circuit is configured to provide a fixed offset current to the V2I resistor node to cause at least one V2I output current to have a value conversely proportional to absolute temperature (CTAT), the at least one V2I output current being output by the V2I converter, and mirror the at least one V2I output current to the CCO to reduce the temperature-induced frequency drift at a lower frequency band of the VCO.