LC VCO Common-Mode Boost for Low-Voltage Start-Up Gain
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Solution Overview
Problem
Voltage-controlled oscillators (VCOs) face challenges in starting up reliably in low-voltage deep submicron CMOS technologies due to reduced supply voltage and increased threshold voltages, leading to insufficient gain for oscillation and limited frequency tuning range.
Innovation Solution
Dynamically adjusting the common mode voltage at the LC tank node and/or power supply voltage of a VCO to temporarily increase gain, allowing for robust start-up without impacting frequency tuning range or phase noise, by using a control circuit to monitor and adjust the common mode voltage to exceed transistor threshold voltages during start-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If supply voltage is reduced to achieve power reduction in low-voltage deep submicron CMOS technologies, then power consumption is reduced, but device threshold voltage increases relative to supply voltage, resulting in insufficient gain for oscillation start-up
Solution Approach 1:
The patent applies preliminary action by temporarily boosting the common mode voltage at the LC tank node before and during the start-up phase. This preliminary voltage adjustment ensures sufficient gain for oscillation to initiate reliably, after which the voltage returns to its normal reduced level for power-efficient operation.
Solution Approach 2:
The patent implements dynamics by making the common mode voltage adjustable and time-dependent. The voltage is dynamically changed from a higher level during start-up to a lower level during steady-state operation, allowing the system to adapt its electrical characteristics based on operational requirements.
2Loss of energy
If device threshold voltage is increased to reduce power drawn from supply and reduce drain-source leakage, then power efficiency is improved, but the voltage difference between common mode voltage and source voltage becomes less than threshold voltage, reducing device transconductance and regenerative loop gain
Solution Approach 1:
The patent applies local quality by selectively adjusting the common mode voltage only at the LC tank node where oscillation occurs, rather than increasing all supply voltages throughout the circuit. This localized adjustment maintains low power consumption in other parts of the circuit while providing sufficient gain where needed.
Solution Approach 2:
The patent uses preliminary action by temporarily increasing the common mode voltage during the start-up phase to ensure sufficient loop gain for oscillation initiation. Once oscillation is established, the voltage returns to its lower normal level, maintaining energy efficiency during steady-state operation.
3Stability of the object's composition
If common mode voltage is maintained at half supply voltage in complementary cross-coupled VCO, then transistor matching and symmetry are optimized, but the voltage difference becomes insufficient to exceed transistor threshold voltages, preventing oscillation start-up
Solution Approach 1:
The patent applies preliminary action by temporarily adjusting the common mode voltage above the standard half-supply level during the start-up phase. This preliminary adjustment ensures that the voltage difference exceeds transistor threshold voltages, enabling oscillation to initiate reliably while maintaining symmetric transistor operation.
Solution Approach 2:
The patent implements dynamics by making the common mode voltage adjustable rather than fixed. The voltage is dynamically increased during start-up to ensure reliable oscillation initiation, then returns to the optimal half-supply level for maintaining transistor matching and symmetry during steady-state operation.
Data Source
AI summary
The present disclosure provides methods and apparatus for dynamically adjusting the common mode voltage at the LC tank node and/or the power supply voltage of a VCO with an LC resonator in order to force oscillation start-up by temporarily increasing gain. Methods according to certain preferred embodiments may reduce power consumption and/or overcome threshold voltage limitations and/or increase frequency and frequency tuning range during normal (steady-state) operation.