Closed-Loop Cascode Amplifier Biasing for Supply Variation Tolerance
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Solution Overview
Problem
Silicon-based CMOS transistors in cascode amplifier circuits face challenges with bias circuits that are not tolerant of supply and bias voltage variations, bias current fluctuations, and poor output resistance characteristics, particularly in applications with varying DC supply voltages and transistor stack heights, leading to poor RF performance and adaptability to changing RF environments.
Innovation Solution
A cascode reference circuit is used to bias the final stages of a cascode amplifier under the control of a closed loop bias control circuit, ensuring the current in the cascode reference circuit is approximately equal to a selected multiple of a known current value by adjusting the gate bias voltage, and incorporating a stack of series-connected CMOS devices to distribute the RF voltage swing, with the closed loop bias control circuit being digitally programmable for dynamic adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bias circuits are used in cascode amplifiers, then the circuit structure is simple, but the bias circuits are not tolerant of supply and bias voltage variations and bias current fluctuations
Solution Approach 1:
The patent implements a closed-loop bias control circuit that continuously monitors the bias current and adjusts the gate bias voltage accordingly. The control circuit compares the actual bias current with a reference current and generates feedback to maintain the desired bias condition, thereby providing tolerance to supply and bias voltage variations while maintaining a manageable circuit structure.
Solution Approach 2:
The patent dynamically adjusts bias parameters (gate bias voltage, bias current) based on operating conditions. By changing these parameters adaptively, the circuit maintains optimal performance across varying supply voltages and bias conditions without requiring a completely complex circuit architecture.
2Ease of manufacture
If silicon-based CMOS transistors are used in cascode amplifiers, then the fabrication cost is low and integration is easy, but the output resistance characteristics are poor
Solution Approach 1:
The patent divides the amplifier into multiple stages with distributed biasing. By segmenting the bias control into separate controllable stages, the circuit can compensate for the inherently poor output resistance of silicon CMOS transistors while maintaining the ease of CMOS fabrication. Each stage can be independently optimized to achieve the desired overall performance.
3Adaptability or versatility
If fixed bias circuits are used, then the circuit design is simple, but the adaptability to changing RF environments is poor
Solution Approach 1:
The patent transitions from fixed bias circuits to dynamic bias control circuits that can adapt to changing RF environments. The control circuit adjusts bias parameters in real-time based on operating conditions, providing adaptability while keeping the circuit complexity manageable through efficient control algorithms and circuit design.
4Use of energy by moving object
If DC supply voltage is varied to optimize operation at different power levels, then the power efficiency is improved, but the bias circuits become less stable
Solution Approach 1:
The closed-loop bias control circuit continuously monitors bias conditions and adjusts gate bias voltages to maintain stable operation even when DC supply voltage varies. The feedback mechanism ensures that power efficiency improvements from voltage variation do not compromise bias stability, as the control circuit compensates for voltage changes in real-time.
Data Source
AI summary
Bias circuits and methods for silicon-based amplifier architectures that are tolerant of supply and bias voltage variations, bias current variations, and transistor stack height, and compensate for poor output resistance characteristics. Embodiments include power amplifiers and low-noise amplifiers that utilize a cascode reference circuit to bias the final stages of a cascode amplifier under the control of a closed loop bias control circuit. The closed loop bias control circuit ensures that the current in the cascode reference circuit is approximately equal to a selected multiple of a known current value by adjusting the gate bias voltage to the final stage of the cascode amplifier. The final current through the cascode amplifier is a multiple of the current in the cascode reference circuit, based on a device scaling factor representing the relative sizes of the transistor devices in the cascode amplifier and in the cascode reference circuit.