Cross-Coupled Amplifier Stage for Low-Current High-Bandwidth Operation
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Solution Overview
Problem
Operational amplifiers with class A or AB output stages face high current consumption and low efficiency, especially in mobile communication systems, due to high quiescent current requirements, which is not effectively addressed without compromising output power or frequency bandwidth.
Innovation Solution
An amplifier stage design featuring a cross-coupled current mirror circuit with differential input signals, auxiliary current paths, and balanced current sources to control quiescent current, allowing for low current consumption while maintaining high frequency bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a class A output stage is used to maintain high frequency bandwidth, then the frequency bandwidth is preserved, but the current consumption increases significantly
Solution Approach 1:
The patent implements a dynamic class AB output stage that automatically adjusts its operating point based on signal conditions. The circuit transitions between class A and class B operation dynamically, maintaining high frequency bandwidth when needed while reducing current consumption during quiescent periods. This is achieved through automatic biasing circuits that adjust the conduction angle of the output transistors based on the signal amplitude and frequency content.
Solution Approach 2:
The patent changes the operating parameters of the output stage by implementing variable biasing conditions. The bias current and voltage are adjusted dynamically to optimize the trade-off between bandwidth and power consumption. By modifying the conduction angle and operating point of the output transistors, the circuit achieves high frequency response only when necessary, while operating in a lower power state during normal conditions.
2Use of energy by moving object
If a class AB output stage is used to reduce current consumption, then the efficiency is improved, but the frequency bandwidth is reduced substantially
Solution Approach 1:
The patent implements a dynamic class AB output stage that automatically adjusts its operating point based on signal conditions. The circuit transitions between class A and class B operation dynamically, maintaining high frequency bandwidth when needed while reducing current consumption during quiescent periods. This is achieved through automatic biasing circuits that adjust the conduction angle of the output transistors based on the signal amplitude and frequency content.
Solution Approach 2:
The patent employs feedback mechanisms to maintain high frequency bandwidth while operating in class AB mode. The feedback circuits monitor the signal characteristics and adjust the biasing conditions accordingly, ensuring that the frequency response remains adequate even when operating at lower power consumption levels. This dynamic feedback control allows the circuit to adapt to varying signal conditions and maintain performance.
3Speed
If additional current paths are added to control output transistor biasing, then the frequency bandwidth is improved, but the area consumption and current consumption increase
Solution Approach 1:
The patent implements multi-functional biasing circuits that serve multiple purposes simultaneously. The same biasing network provides both frequency compensation and output transistor biasing, eliminating the need for separate dedicated circuits. This integration reduces the overall circuit area while maintaining the necessary frequency bandwidth through shared functional elements that perform multiple roles in the signal path.
Data Source
AI summary
An amplifier stage includes a first and a second signal path having a series connection of a first transistor of a first conduction type which forms a control input for receiving an input signal to the amplifier stage and a second transistor of a second conduction type. The amplifier stage further includes a first and second signal output which are formed by a respective connection node of the respective first and second transistors. For each of the first and the second signal path, the amplifier stage includes a third transistor of the second conduction type which is connected to the respective second transistor as current mirror, and a fourth transistor of the first conduction type which is connected to the respective first transistor as a current mirror and which is for controlling the third transistor of the other signal path, respectively. Furthermore, for each of the first and the second signal path, a current source is provided with is connected in parallel to one of the respective first, second, third, and fourth transistors.