Cascode CMOS Power Amplifier Biasing for Baseband Signal Removal
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Solution Overview
Problem
Power amplifiers based on the CMOS process face challenges in linearity due to low breakdown voltage characteristics and difficulty in coupling with control circuit blocks, particularly due to the generation of baseband frequency signals at the common gate node in cascode structures.
Innovation Solution
A power amplifier design that includes a bias supply unit capable of controlling the impedance at the common gate node by using resistors, capacitors, and bonding wires to remove baseband frequency signals, and optionally incorporating diodes and switches to manage power modes and impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large resistor is inserted at the bias line of the common gate terminal to form an RF open state, then the bias power can be supplied to the common source amplifier, but baseband frequency signals are detected at the common gate node which reduce the linearity of the amplifier
Solution Approach 1:
An inductor is introduced as an intermediary component connected between the common gate node and ground. This inductor acts as a frequency-selective path that allows baseband frequency signals to be shunted to ground while maintaining the RF open state through the large resistor, thereby eliminating the harmful baseband signals without affecting the bias power supply function
Solution Approach 2:
The impedance characteristics at the common gate node are modified by adding the inductor, which changes the frequency-dependent behavior of the node. The inductor provides a low-impedance path specifically for baseband frequencies while maintaining high impedance for RF frequencies, thus selectively removing harmful signals while preserving the desired operating conditions
2Ease of manufacture
If a cascode structure with two transistors stacked is used in CMOS process, then the power amplifier can be implemented, but the low breakdown voltage characteristics of CMOS elements limit the performance compared to HBT process
Solution Approach 1:
The inductor serves as a mediator that enables the CMOS cascode structure to achieve HBT-like performance by selectively removing baseband signals that degrade linearity. This allows CMOS technology to compete with HBT in terms of performance while maintaining the manufacturing advantages of CMOS process
3Power
If bias power is supplied to the common gate node, then the common source amplifier can operate, but the nonlinear characteristics of the amplifier generate baseband signals that reduce linearity
Solution Approach 1:
The inductor converts the harmful baseband signals generated by nonlinear characteristics into a beneficial situation by providing a dedicated low-impedance path to ground for these frequencies. This transforms the problematic baseband signals from degrading factors into controlled elements that can be efficiently shunted away, improving overall amplifier linearity while maintaining full amplifying operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances the linearity of the power amplifier by effectively removing baseband frequency signals, improving the asymmetry and sideband signal characteristics, and increasing the power added efficiency and reducing third-order intermodulation distortion.
Implementation Method 1
The bias supply unit may control an impedance of harmonic components of the common gate node according to an inductance component of a bonding wire connected to a ground.
Implementation Method 2
a first capacitor connected to be parallel to the first resistor
Data Source
AI summary
There is provided a power amplifier including an amplifying unit having at least two cascode amplifiers connected in parallel to amplify an input signal; and a bias supply unit supplying bias power to a common gate node of the two cascode amplifiers, and removing a signal of a pre-set frequency band corresponding to a baseband at the common gate node by controlling impedance of the common gate node.