Adaptive Biasing in LC and Ring VCOs for Low Noise Startup
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Solution Overview
Problem
Voltage controlled oscillators (VCOs) are power hungry and noisy, and existing low noise and low power designs for LC tank and ring-based VCOs are challenging due to dependence on process variations and temperature.
Innovation Solution
The design incorporates a biasing circuit that makes the transconductance of transistors proportional to the inverse of parallel equivalent resistance, allowing the startup condition for oscillation to be independent of temperature and process variations, and uses voltage-controlled resistors to control the oscillation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional VCO architectures are used, then oscillation function is achieved, but power consumption is high and phase noise is high
Solution Approach 1:
The patent changes the biasing parameters dynamically by making the tail current proportional to the inverse of the parallel equivalent resistance through a biasing circuit. This parameter change allows the VCO to adapt to process and temperature variations, achieving low phase noise while maintaining low power consumption across different operating conditions.
Solution Approach 2:
The biasing circuit automatically adjusts the tail current based on the actual parallel equivalent resistance of the inductors, making the system self-regulating. The VCO self-adjusts its bias conditions to compensate for process variations and temperature drift without external intervention, thereby maintaining optimal noise and power performance.
2Device complexity
If fixed bias current is used, then circuit is simple, but oscillation startup condition depends on process variations and temperature
Solution Approach 1:
The biasing circuit implements feedback by sensing the parallel equivalent resistance and adjusting the tail current accordingly. The feedback mechanism ensures that the oscillation startup condition (gm*Rp >= 1) is always satisfied regardless of process variations or temperature changes, while adding minimal circuit complexity.
Solution Approach 2:
The patent transitions from a static fixed bias current to a dynamic bias current that automatically adapts to changing operating conditions. The tail current becomes a function of the parallel equivalent resistance, allowing the circuit to maintain reliable oscillation startup across different processes and temperatures without becoming overly complex.
3Reliability
If high tail current is used to ensure oscillation startup, then oscillation reliability is improved, but power consumption increases
Solution Approach 1:
Instead of using a fixed high tail current, the patent changes the biasing parameter to be adaptive - the tail current is made proportional to the inverse of the parallel equivalent resistance. This allows the current to be just sufficient for reliable startup under each specific operating condition, minimizing power consumption while ensuring oscillation reliability.
Data Source
AI summary
LC tank and ring-based VCOs are disclosed that each include a differential pair of transistors for steering a tail current generated by a current source responsive to a bias voltage. A biasing circuit generates the bias voltage such that a transconductance for the transistors in the differential pairs is inversely proportional to a resistance.