Pre-Driver Multi-Stage Amplifier for Wider Bandwidth and High Gain
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Solution Overview
Problem
Existing multi-stage amplifiers face challenges in extending bandwidth while maintaining high open-loop gain due to the nested Miller feedback loop, which limits their useful bandwidth and reduces open-loop gain.
Innovation Solution
A multi-stage amplifier configuration with a low output impedance pre-driver stage and a rail-to-rail output stage, utilizing a single Miller feedback loop and translinear loops to stabilize the amplifier, allowing for increased bandwidth without sacrificing open-loop gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a nested Miller feedback loop is used to stabilize the amplifier, then stability is improved, but bandwidth is limited and open-loop gain is reduced
Solution Approach 1:
The patent extracts the stabilizing function from the nested Miller feedback loop and implements it through a simplified single Miller feedback loop combined with a specific pre-driver stage configuration. By removing the nested structure and using emitter-coupled transistors with tailored impedance, the patent achieves stability without the bandwidth limitations imposed by multiple feedback capacitors
Solution Approach 2:
The patent changes the impedance parameters of the pre-driver stage to achieve low output impedance, which fundamentally alters how the Miller feedback loop operates. By adjusting transistor sizing and coupling configurations, the patent transforms the pre-driver from a high impedance stage to a low impedance stage, enabling bandwidth extension while maintaining stability through a single feedback loop
2Stability of the object's composition
If a nested Miller feedback loop is used to stabilize the amplifier, then stability is improved, but open-loop gain is reduced
Solution Approach 1:
The patent extracts the stabilizing function from the nested Miller feedback loop and implements it through a simplified single Miller feedback loop combined with a specific pre-driver stage configuration. By removing the nested structure and using emitter-coupled transistors with tailored impedance, the patent achieves stability without the gain reduction caused by multiple feedback capacitors
Solution Approach 2:
The patent introduces dynamic behavior through the emitter-coupled pre-driver stage, where the transistors automatically adjust their operating points based on signal conditions. This dynamic operation allows the circuit to maintain high gain at low signal levels while providing stability through the controlled impedance transformation, eliminating the need for gain-reducing feedback networks
3Adaptability or versatility
If a high output impedance Class AB pre-driver stage is used, then rail-to-rail output capability is achieved, but bandwidth is limited
Solution Approach 1:
The patent inverts the conventional approach by designing a low output impedance pre-driver stage instead of a high output impedance stage. This inversion, combined with emitter-coupled transistor configuration, allows the circuit to drive the rail-to-rail output stage effectively while extending bandwidth, proving that low impedance can also achieve full output swing capability
Solution Approach 2:
The emitter-coupled pre-driver stage acts as an intermediary between the input and output stages, providing impedance transformation and signal conditioning. By using the emitter coupling as a mediator, the patent achieves both bandwidth extension and rail-to-rail output capability, as the intermediary stage can adapt to both high and low impedance requirements
Data Source
AI summary
A multi-stage amplifier including a pre-driver stage, and method of operating the same. In one example, the amplifier includes an output stage with a first output transistor coupled to an oppositely doped second output transistor and to an output terminal. The pre-driver stage includes with a first driver transistor coupled to the first output transistor, and a second driver transistor coupled to the second output transistor. The pre-driver stage also includes a first current mirror and a second current mirror coupled to the first driver transistor and the second driver transistor. The pre-driver stage also includes a first translinear loop having a first translinear loop transistor and a second translinear loop having a second translinear loop transistor coupled to the first output transistor and the second output transistor.