Stacked FET Amplifier Gate RC Network for Source Impedance Control
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Solution Overview
Problem
Existing stacked FET amplifiers face challenges in controlling both real and imaginary parts of source impedances, leading to efficiency losses, non-linear distortion, and reliability issues, especially at higher frequencies due to unmanaged phase shifts and reactance components.
Innovation Solution
The implementation of a compensation network comprising a series-connected resistive-capacitive network coupled to the gate of each cascode transistor, which controls both the real and imaginary parts of the source impedance, ensuring aligned current phases and improved performance across a range of frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gate capacitors are configured to distribute RF voltage across drain-source nodes of stacked transistors, then RF voltage control is improved, but imaginary part of source impedance cannot be controlled leading to phase shifts
Solution Approach 1:
A compensation network is introduced as an intermediary element connected to the gate of each cascode transistor. This network includes a series resistive-capacitive circuit that acts as a mediator to control both real and imaginary parts of source impedance, thereby enabling phase alignment of currents without directly modifying the transistor structure itself.
Solution Approach 2:
The invention changes the impedance parameters by introducing adjustable resistive and capacitive elements in the compensation network. By tuning the resistance and capacitance values in the series RC circuit, both real and imaginary parts of the source impedance can be independently controlled to achieve desired current phase alignment across different operating frequencies.
2Speed
If stacked FET amplifiers operate at higher frequencies, then bandwidth is improved, but unmanaged reactance components cause efficiency losses and distortion
Solution Approach 1:
The compensation network provides a feedback mechanism where the series resistive-capacitive circuit senses the impedance conditions at the gate of each cascode transistor and adjusts the effective source impedance accordingly. This feedback control ensures that reactance components are compensated across the operating bandwidth, maintaining efficiency at higher frequencies.
Solution Approach 2:
By changing the frequency-dependent behavior of the capacitive elements in the compensation network, the invention enables dynamic adjustment of impedance parameters across the operating frequency range. The capacitive reactance varies with frequency to counteract the parasitic reactances that increase at higher frequencies, thereby maintaining amplifier efficiency.
3Measurement precision
If gate capacitors are used to control real part of source impedance, then RF voltage distribution is improved, but imaginary part remains uncontrolled causing phase shifts
Solution Approach 1:
The compensation network serves as an intermediary between the gate control mechanism and the source impedance. The series resistive-capacitive circuit within this network provides separate control paths for real and imaginary impedance components, enabling independent adjustment of each parameter to ensure both voltage distribution and current phase alignment.
Solution Approach 2:
The invention segments the impedance control function into two independent control mechanisms: gate capacitors for controlling the real part of source impedance, and the compensation network with series RC circuit for controlling the imaginary part. This segmentation allows each component to be optimized for its specific function without interfering with the other.
4Reliability
If compensation network with series resistive-capacitive network is added, then impedance control is improved, but device complexity increases
Solution Approach 1:
The compensation network is designed to perform multiple functions simultaneously: it controls both real and imaginary parts of source impedance, provides phase alignment, and maintains voltage distribution across the stacked transistors. The series resistive-capacitive circuit serves as a multi-functional element that addresses multiple impedance control requirements through a single integrated structure.
Solution Approach 2:
The invention merges the impedance control function with the existing gate biasing structure by connecting the compensation network to the gate terminal. This merging approach integrates the new control mechanism into the existing circuit topology, minimizing additional complexity while achieving enhanced impedance control precision.
Data Source
Figure 1A
Figure 1B
Figure 1C~1D
AI summary
Apparatuses for controlling impedance in intermediate nodes of a stacked FET amplifier are presented. According to one aspect, a series-connected resistive and capacitive network (Zg21, ..., Zgn1) coupled to a gate of a cascode FET transistor (M2, ..., Mn) of the amplifier provide control of a real part and an imaginary part of an impedance looking into a source of the cascode FET transistor (M2, ..., Mn). According to another aspect, a second parallel-connected resistive and inductive network (Zg22, ..., Zgn2) coupled to the first network provide further control of the real and imaginary parts of the impedance. According to another aspect, a combination of the first (Zg21, ..., Zgn1) and the second (Zg22, ..., Zgn2) networks provide control of the impedance to cancel a reactance component of the impedance. According to another aspect, such combination provides control of the real part for distribution of an RF voltage output (RFOUT) by the amplifier across stacked FET transistors of the amplifier (M1, M2, ..., Mn).