Cascode Amplifier Bias Circuit With Closed-Loop Current Scaling
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Solution Overview
Problem
Silicon-based CMOS cascode amplifier circuits face challenges in tolerating supply and bias voltage variations, bias current variations, and transistor stack height, particularly due to poor output resistance characteristics and low breakdown voltage, which affects their performance in changing RF environments.
Innovation Solution
The implementation of a cascode reference circuit with a closed loop bias control circuit that dynamically adjusts the gate bias voltage to maintain a consistent current multiple, accommodating arbitrary supply voltage variations and improving output resistance by matching drain and gate voltages across stages, while also allowing for digital programmability to adapt to changing RF conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based CMOS cascode amplifier circuits are used, then cost and integration complexity are reduced, but output resistance characteristics deteriorate and breakdown voltage decreases
Solution Approach 1:
The amplifier is divided into multiple cascode stages with separate bias control circuits for each stage. Each stage can be independently biased to optimize output resistance characteristics while maintaining CMOS integration benefits. The segmentation allows each transistor stack to operate at optimized voltage points.
Solution Approach 2:
Dynamic bias control circuits are implemented that can adjust gate bias voltages in real-time based on operating conditions. This dynamic adjustment compensates for the inherently poor output resistance of silicon CMOS devices by adapting the bias point to maintain optimal performance across varying supply voltages and temperatures.
2Use of energy by moving object
If supply voltage is reduced for portability, then power consumption decreases, but amplifier performance and linearity deteriorate
Solution Approach 1:
The bias control circuits dynamically adjust gate-source voltage parameters to maintain optimal amplifier performance across a wide range of supply voltages. By changing the bias parameters adaptively, the amplifier maintains linearity and performance even when supply voltage is reduced for portable applications.
Solution Approach 2:
Feedback mechanisms are implemented in the bias control circuits that monitor the actual operating point and adjust bias voltages accordingly. This feedback ensures that amplifier performance metrics such as linearity and gain are maintained despite variations in supply voltage, enabling portable devices to achieve both low power consumption and high performance.
3Strength
If cascode amplifier stages are added to increase voltage handling, then breakdown voltage tolerance improves, but device complexity increases
Solution Approach 1:
The cascode amplifier stages are designed with universal bias control circuits that can be applied to transistor stacks of varying heights. The same bias control architecture works whether there are 2, 3, or more transistors in the stack, providing multi-functionality. This allows the circuit to handle higher voltages through increased stack height without proportionally increasing control complexity.
Solution Approach 2:
Standardized cascode stage modules are created that can be replicated and stacked to achieve the required voltage handling. Each module contains the necessary transistors and associated bias control circuitry, and multiple identical modules can be stacked in series. This copying approach increases voltage tolerance through stack height while keeping the complexity of each individual module manageable and reusable.
4Adaptability or versatility
If bias control circuits are made highly adaptive to tolerate voltage variations, then supply voltage tolerance improves, but circuit complexity increases
Solution Approach 1:
The bias control circuits are designed to automatically adjust and self-regulate without requiring complex external control logic. Each bias control circuit monitors its own stage's operating conditions and autonomously adjusts the gate bias voltages to maintain optimal performance. This self-service capability provides high supply voltage tolerance while keeping the control circuitry relatively simple and localized to each stage.
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.