Class AB Cascode Stage Filtering for High-Frequency Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Static class AB amplifiers suffer from high-frequency distortion due to variations in transconductance and output resistance, which cannot be suppressed by loop gain, affecting their linearity and failing to meet strict FCC requirements for third-order intermodulation distortion.
Innovation Solution
Incorporating a cascode stage with a high-pass filter to generate driving signals with AC components, increasing gain at high frequencies and reducing voltage swings, thereby improving the amplifier's linearity by reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a static class AB amplifier uses a stage before the output stage to set DC levels, then the output stage can be properly biased, but the variations in transconductance and output resistance generate high-frequency distortion
Solution Approach 1:
The patent introduces a cascode stage as an intermediary between the input stage and output stage. This cascode stage includes a filter that processes the input signal before it reaches the output stage, thereby mediating the signal path to prevent distortion generation while still allowing proper DC biasing to occur
Solution Approach 2:
The patent modifies the signal parameters by introducing a filter in the cascode stage that changes the frequency characteristics of the signal. The filter attenuates high-frequency components that would otherwise cause distortion, while maintaining the necessary DC levels for proper output stage operation
2Reliability
If loop gain is used to suppress distortion, then linearity can be improved at low frequencies, but loop gain cannot suppress high-frequency distortion
Solution Approach 1:
The patent applies preliminary action by filtering the input signal before it reaches the output stage through the cascode stage. The filter pre-processes the signal to remove problematic high-frequency components before amplification, preventing distortion from occurring in the first place rather than attempting to correct it afterward
Solution Approach 2:
The cascode stage with its integrated filter acts as an intermediary that modifies the signal characteristics before the output stage processes it. This intermediary stage ensures that high-frequency components are appropriately filtered while maintaining signal integrity for the intended frequency range
3Reliability
If the amplifier meets strict FCC requirements for third-order intermodulation distortion, then compliance is achieved, but the complexity of the amplifier increases
Solution Approach 1:
The patent merges the filter function directly into the cascode stage, combining multiple functions (DC level setting, signal filtering, and driving the output stage) into a single integrated stage. This reduces overall amplifier complexity compared to adding separate filter circuits while still achieving FCC compliance
Solution Approach 2:
The cascode stage is designed to perform multiple functions simultaneously: it sets DC levels for the output stage, filters high-frequency components to reduce distortion, and provides proper signal driving. This multi-functionality reduces the need for additional separate components, maintaining simplicity while achieving compliance
Data Source
AI summary
The present invention provides a class AB amplifier, wherein the class AB amplifier includes a cascode stage with a filter and an output stage. The cascode stage with the filter is arranged for receiving an input signal to generate a first driving signal and a second driving signal, wherein the filter filters the input signal to generate an filtered input signal, and at least one of the first driving signal and the second driving signal is generated according to the filtered input signal. The output stage is coupled to the cascode stage, and is arranged for generating an output signal according to the first driving signal and the second driving signal.