Push-Pull Class A Amplifier Biasing Using DC Common-Mode Extraction
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Solution Overview
Problem
Conventional amplifier classes, such as class A and class AB, face challenges in providing the necessary operating parameters for certain electronic circuits, including high power consumption, noise addition, and limited push-pull capability, which are undesirable for applications like continuous time delta sigma modulators.
Innovation Solution
The implementation of an amplifier circuit with a differential input stage, a common mode circuit to extract DC common mode voltage, and a bias circuit to bias output devices, enabling push-pull capability while maintaining a small area and reducing noise, by using a configuration that includes diode-connected transistors and back gate biasing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional class A amplifier is used, then low noise and high linearity are achieved, but power consumption is high and push-pull capability is limited
Solution Approach 1:
The amplifier is divided into two stages: a first amplifier stage and a second amplifier stage. The first stage processes the input signal with high linearity and low noise, while the second stage provides push-pull output capability. This segmentation allows each stage to be optimized for its specific function, resolving the contradiction between signal quality and power consumption.
Solution Approach 2:
The second amplifier stage operates in a dynamic class AB manner, allowing the output devices to switch between active and inactive states based on the signal requirements. This dynamic operation provides push-pull capability while maintaining efficiency, addressing the power consumption issue of conventional class A amplifiers.
2Adaptability or versatility
If conventional class AB amplifier is used, then push-pull capability is improved, but noise and distortion increase
Solution Approach 1:
By separating the amplification function into two stages, the first stage maintains low noise and distortion characteristics while the second stage provides push-pull capability. The segmentation prevents the noise and distortion typically associated with class AB operation from affecting the overall signal quality.
Solution Approach 2:
The first amplifier stage acts as an intermediary between the input signal and the second amplifier stage. It conditions the signal with high fidelity before passing it to the second stage, which then provides the push-pull output. This intermediary function isolates the signal from the noise-generating mechanisms of the push-pull stage.
3Area of stationary object
If amplifier size is reduced, then area is minimized, but achieving appropriate operating parameters becomes difficult
Solution Approach 1:
The patent utilizes the third dimension (vertical stacking) by coupling the first and second amplifier stages in a cascaded configuration. This allows multiple functional blocks to be integrated in a compact footprint, achieving both small area and appropriate operating parameters through three-dimensional circuit design.
Solution Approach 2:
The bias circuit dynamically adjusts the operating parameters of the second amplifier stage based on the common mode voltage from the first stage. This parameter adaptation allows the amplifier to maintain optimal performance across different operating conditions while occupying minimal area.
Data Source
AI summary
An amplifier circuit comprises a first amplifier circuit stage including input devices connected to inputs of the amplifier circuit, a second amplifier circuit stage coupled to the first amplifier stage, a common mode extraction circuit configured to extract a DC common mode voltage of the first amplifier stage, and a bias circuit configured to bias one or more output devices of the second amplifier circuit stage using the DC common mode voltage.