Cascode Amplifier Current Injection for High-Frequency Linearity
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Solution Overview
Problem
Cascode amplifiers suffer from distortion due to non-linear current conduction by the cascode stage, especially at high frequencies, which affects the linearity of the output signal.
Innovation Solution
Incorporating a current injection circuit that generates out-of-phase injection currents and applies them to the cascode transistor, creating a local current loop that directs non-linear current away from parasitic capacitances, thereby reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a cascode amplifier is used to achieve high frequency operation and voltage gain, then bandwidth and impedance characteristics are improved, but non-linear current conduction by the cascode stage causes distortion and reduced linearity
Solution Approach 1:
The patent applies preliminary anti-action by introducing a current injection circuit that generates anti-phase currents before the non-linear effects can significantly distort the output. The injection circuit detects the input signal and produces compensating currents that are injected into the cascode transistor's current terminals, preemptively counteracting the non-linear current conduction that would otherwise occur during high-frequency operation.
Solution Approach 2:
The current injection circuit acts as an intermediary between the input signal and the cascode transistor. It processes the input signal and generates injection currents that mediate the interaction between the signal and the non-linear cascode stage, reducing the harmful non-linear effects while preserving the desired amplification and bandwidth characteristics.
2Reliability
If the cascode stage is added to eliminate direct coupling between output and input, then input-output isolation is improved, but non-linear current conduction increases distortion
Solution Approach 1:
The patent converts the harmful non-linear current conduction into a beneficial effect by using the same cascode transistor that generates the non-linearity to also provide the solution. The current injection circuit exploits the transistor's own characteristics and injects compensating currents that transform the non-linear behavior into a more linear overall response, effectively converting the harm into a benefit.
3Manufacturing precision
If a current injection circuit is added to reduce distortion, then linearity is improved, but device complexity increases
Solution Approach 1:
The current injection circuit is designed to perform multiple functions: it provides distortion compensation, maintains input-output isolation, and works across a broad frequency range. By integrating these functions into a single circuit block that shares components with the existing amplifier structure, the patent reduces the overall complexity increase while achieving multiple performance improvements simultaneously.
Data Source
AI summary
A cascode amplifier including an amplifier transistor, a cascode transistor, and a current injection circuit. The amplifier transistor has a first current terminal receiving a first power supply voltage, a second current terminal, and a control terminal receiving an input signal. The cascode transistor has a first current terminal coupled to the second current terminal of the amplifier transistor, a second current terminal coupled to an output terminal; and a control terminal receiving a bias voltage. The current injection circuit has an input receiving the input signal, and first and second outputs coupled to the first and second current terminals of the cascode transistor, respectively. The current injection circuit is configured to present out-of-phase currents to the cascode transistor responsive to the input signal.