PLL VCO Bias Current Control for Temperature Drift Compensation
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Solution Overview
Problem
Voltage-controlled oscillators (LC-VCOs) in phase-locked loops face challenges with temperature drift, as the limited range of control voltage restricts their ability to accommodate temperature changes, leading to potential PLL lock loss, especially in advanced CMOS technology nodes, where the tuning voltage has less room for counteraction.
Innovation Solution
An electronic control device and method that provide a bias current change to maintain the control voltage within a specified range, using a secondary control loop with a voltage-to-current converter and low-pass filter, allowing for temperature desensitization without additional control elements, and incorporating a difference amplifier to compare and adjust the control voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the control voltage range is limited in advanced CMOS technology nodes, then the power consumption is reduced, but the ability to accommodate temperature drift is worsened
Solution Approach 1:
The patent changes the control parameter from voltage-only to current-based control. By using a bias current that varies with temperature (having a positive temperature coefficient) to control the VCO, the system can compensate for temperature drift without requiring a larger voltage range. This parameter change allows the system to maintain adaptability to temperature changes while operating within the limited voltage supply range of advanced CMOS nodes.
2Reliability
If a second point injection with additional varactors is used to compensate drift, then the temperature compensation is improved, but the parasitics in the LC tank increase
Solution Approach 1:
The patent extracts the temperature compensation function from the VCO's LC tank circuit by implementing it in the bias current generation stage. Instead of adding compensation elements (varactors) directly to the LC tank, the temperature compensation is achieved by generating a temperature-dependent bias current that controls the VCO frequency. This separation eliminates the harmful parasitics that would result from adding additional varactors to the tank circuit.
3Reliability
If conventional bias-current based compensation uses PTAT/CTAT currents, then the temperature drift compensation is provided, but the frequency error compensation capability is limited
Solution Approach 1:
The patent implements a feedback mechanism where the bias current is dynamically adjusted based on the actual frequency error detected by the PLL. The frequency error signal is used to modulate the bias current, creating a closed-loop system that can compensate for both temperature drift and other frequency errors. This feedback approach provides greater versatility compared to open-loop PTAT/CTAT current compensation, as it can adapt to various sources of frequency deviation.
Data Source
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AI summary
Electronic control device (200), comprising: - a first input (201) for a control voltage (Vtune) of a voltage controlled device (200); - a second input (202) for a reference control voltage (Vtune0) of the voltage controlled device (200); and - an output (203), wherein - the electronic control device (200) is configured to provide a bias current change (ΔIB) via the output (203) to the voltage controlled device (200) in order to maintain a level of the control voltage (Vtune) inside a specified range.