Cascode Amplifier Linearity with Phase-Shifted Auxiliary Common-Gate Path
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Solution Overview
Problem
Cascode amplifiers in integrated circuits face a challenge in reducing third-order inter-modulation distortion (IMD3) without significantly reducing signal gain, as existing techniques that use auxiliary signal paths often compromise amplifier gain to cancel IMD3 components.
Innovation Solution
The implementation of a phase shifting network that couples the cascode node signal to the source of a common-gate amplifier, allowing for IMD3 cancellation without decreasing the desired signal gain, by increasing the auxiliary current to offset the increase in principal cascode current, thereby maintaining or enhancing signal gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an auxiliary signal path is coupled in parallel with the principal cascode signal path to cancel IMD3 components, then the level of IMD3 in the output is reduced, but the signal gain of the cascode amplifier is significantly reduced
Solution Approach 1:
A phase shifting network is introduced as an intermediary component between the cascode node and the auxiliary common-gate amplifier. This network selectively phase-shifts IMD3 components while passing the desired signal with minimal phase shift, enabling the auxiliary amplifier to generate a cancellation signal that targets only the distortion components without significantly affecting the main signal gain
Solution Approach 2:
The phase shifting network applies different phase shift characteristics to different frequency components of the signal. Specifically, it applies a larger phase shift to IMD3 components (which are at higher frequencies) and a smaller phase shift to the desired signal frequencies, thereby enabling selective cancellation of distortion components while preserving signal gain
Data Source
AI summary
Techniques for improving the linearity of a cascode amplifier. In an exemplary embodiment, an auxiliary common-gate amplifier is provided in parallel with the principal cascode branch. The auxiliary common-gate amplifier samples a cascoded node in the principal cascode branch. The auxiliary common-gate amplifier generates a current which, when combined with the current generated by the principal cascode branch, cancels a distortion component to generate an output current with improved linearity characteristics. In an exemplary embodiment, a phase shifting network couples the cascoded node to the auxiliary common-gate amplifier, and may include, e.g., a capacitor coupled to an inductor.