Ring VCO Bias Circuit for Process-Independent Startup
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing low-power voltage controlled oscillators (VCOs) are sensitive to process corners, temperatures, and supply voltage variations, leading to inefficient power consumption and startup conditions that are not independent of these factors.
Innovation Solution
A ring oscillator design with differential inverters and a bias circuit that generates a bias voltage, where transconductance is proportional to the ratio of device widths, and the use of switching-capacitor circuits to replace adjustable resistances, making the oscillation frequency and startup conditions independent of process corners and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ring oscillator design is used, then oscillation can be achieved, but power consumption is high and startup conditions are sensitive to process corners and temperature
Solution Approach 1:
The patent changes the biasing parameters by using a bias circuit that generates a bias voltage to set the transconductance of transistors in the differential pairs. The transconductance is made proportional to a factor that is a function of the ratio of device widths within the bias circuit, creating a self-adjusting mechanism that compensates for process and temperature variations without requiring excessive power.
Solution Approach 2:
The patent replaces traditional resistive biasing elements with switching-capacitor circuits. These circuits use capacitive reactance instead of resistance to control the bias conditions, which provides temperature and process independence because capacitive values are less sensitive to these variations compared to resistive values. This substitution enables the VCO to maintain stable startup conditions across different operating conditions with lower power consumption.
2Adaptability or versatility
If adjustable resistances are used to control oscillation frequency, then frequency tuning is possible, but the circuit becomes sensitive to process corners and temperature variations
Solution Approach 1:
The patent substitutes adjustable resistances with switching-capacitor circuits for frequency control. The switching-capacitor circuits use capacitive elements whose values can be adjusted through switching networks, providing frequency tuning capability. Since capacitive values are inherently more stable across process corners and temperature compared to resistive values, this substitution maintains frequency tuning versatility while improving reliability and insensitivity to environmental variations.
Solution Approach 2:
The patent changes the control parameter from resistive to capacitive. By using switching-capacitor circuits, the frequency tuning mechanism relies on changing capacitive reactance rather than resistance. This parameter change exploits the fact that capacitance values are less affected by process variations and temperature, thereby maintaining adaptability for frequency control while achieving the desired insensitivity to environmental factors.
3Reliability
If high bias current is used to ensure startup across all conditions, then startup reliability improves, but power consumption increases
Solution Approach 1:
The patent changes the biasing approach by using a bias circuit that dynamically adjusts the bias voltage based on the ratio of device widths in the differential pairs. This creates a self-regulating mechanism where the transconductance is optimized for reliable startup without requiring excessively high bias currents. The parameter change from fixed high current biasing to ratio-dependent voltage biasing enables startup reliability with reduced power consumption.
Solution Approach 2:
The patent implements a self-service mechanism where the bias circuit automatically adjusts the bias conditions based on the intrinsic device width ratios of the differential pairs. This self-adjusting biasing system ensures that the VCO starts up reliably across different process corners and temperatures without requiring external high-power intervention or manual calibration, thereby achieving startup reliability with minimal power overhead.
Data Source
AI summary
In one embodiment, a voltage-controlled oscillator (VCO) is provided that includes: a plurality of differential inverters coupled to form a loop, each differential inverter having a differential pair of transistors configured to steer a tail current from a current source, the current source sourcing the tail current responsive to a bias voltage, wherein each transistor in the differential pair couples to a power source through a corresponding switching-capacitor circuit; and a bias circuit configured to generate the bias voltage such that a transconductance for each transistor in the differential pairs is proportional to a factor that is a function of a ratio of transistor widths within the bias circuit.