Self-Biased VCO Biasing Circuit for Low Noise and High PSRR
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Solution Overview
Problem
Conventional biasing methods for voltage controlled oscillators (VCOs) fail to meet modern requirements for low noise and low power consumption due to inadequate voltage headroom, temperature variations, and low power supply rejection ratio (PSRR), leading to increased noise and instability.
Innovation Solution
A biasing circuit utilizing a triode resistor and self-biasing circuit to provide a stable voltage, canceling temperature effects and enhancing PSRR, while adjusting incoming voltage to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap biasing is used to bias the VCO, then the VCO can be biased with a reference voltage, but the voltage headroom is insufficient and noise increases
Solution Approach 1:
The patent changes the biasing parameters by using a self-biasing circuit that generates a bias voltage dynamically adapted to the supply voltage, rather than using a fixed bandgap reference. This allows the circuit to maintain proper bias conditions across different supply voltages while preserving sufficient voltage headroom for low-noise operation.
Solution Approach 2:
The self-biasing circuit automatically adjusts its own bias voltage based on the supply voltage level, eliminating the need for an external bandgap reference. The circuit services itself by generating the appropriate bias conditions internally, adapting to varying supply conditions while maintaining low noise performance.
2Reliability
If conventional bandgap biasing is used, then bias reference is provided, but power consumption increases and PSRR decreases
Solution Approach 1:
The self-biasing circuit generates its own bias voltage without requiring a power-intensive bandgap reference circuit. By using simple voltage division and buffering stages, the circuit achieves bias reference functionality with minimal power consumption, directly addressing the energy loss problem.
Solution Approach 2:
The patent extracts the essential bias reference functionality from the complex bandgap circuit and implements it through a simplified self-biasing approach. Only the necessary bias generation elements are retained, eliminating the power-consuming components of conventional bandgap circuits while maintaining bias stability.
3Reliability
If conventional biasing circuits are used, then bias current is provided, but temperature variations cause instability
Solution Approach 1:
The self-biasing circuit dynamically adjusts the bias voltage parameter in response to temperature variations, rather than using a fixed reference. This allows the bias current to remain stable across temperature changes by automatically compensating for thermal effects through the voltage division network.
4Reliability
If conventional biasing is used, then VCO operation is maintained, but noise increases due to low PSRR
Solution Approach 1:
The self-biasing circuit changes the bias voltage parameter to optimize the operating point of the VCO, improving PSRR and reducing noise. By dynamically adjusting the bias conditions rather than using a fixed reference, the circuit maintains optimal noise performance across varying supply conditions.
Data Source
AI summary
A system and method for voltage controlled oscillator (VCO) biasing in low voltage circuits including low resistance elements that are especially susceptible to noise. In one embodiment, a poly resistor and triode resistor is used to cancel or offset the effects that temperature variations have on the circuit. The triode resistor is powered by a voltage source that uses a pair of diodes coupled to a constant transconductance (gm) circuit to generate a reduced noise voltage that is independent of the power supply noise. The size of the triode resistor and poly resistors can be varied.