Cascode HEMT-HBT Power Amplifier Cutoff Bias
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Solution Overview
Problem
In fifth-generation mobile communication systems, the increased frequency band leads to higher power loss in radio frequency circuits, necessitating higher gain and output for radio-frequency power amplifiers, while existing power amplifiers using enhancement-type field effect transistors suffer from significant power consumption due to non-negligible drain current at zero gate voltage, reducing talk time in communication devices.
Innovation Solution
A power amplifier design incorporating a cascode-connected high electron mobility transistor and heterojunction bipolar transistor configuration, where the heterojunction bipolar transistor is brought into a cutoff region at zero voltage, preventing drain current flow and reducing power consumption, utilizing a choke inductor and bias circuits to manage bias voltages and suppress wasteful current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an enhancement-type field effect transistor is used as the initial-stage amplifier element to operate the power amplifier only with a positive power supply, then the power amplifier can eliminate a negative power supply, but the drain current Idss cannot be completely cut off even when the gate voltage is set to 0 V, resulting in increased power consumption
Solution Approach 1:
A bias circuit is introduced as an intermediary component between the power supply and the enhancement-type field effect transistor. The bias circuit generates and supplies a negative bias voltage to the gate terminal of the transistor, enabling complete cutoff of the drain current Idss even though the power amplifier itself operates with only a positive power supply. This resolves the contradiction by adding a control mechanism without complicating the main power supply configuration.
2Ease of operation
If the drain current Idss flows in a non-negligible amount at zero gate voltage, then the power amplifier can operate with positive power supply only, but the power consumption of the battery increases, shortening the talk time
Solution Approach 1:
The bias circuit acts as an intermediary that decouples the simplicity of single-power-supply operation from the need for current cutoff. It provides the necessary negative gate voltage to eliminate Idss flow during standby, thereby extending battery talk time while maintaining ease of operation with a single positive power supply.
Solution Approach 2:
The bias circuit dynamically changes the gate voltage parameter from 0 V to a negative value, transforming the transistor's operating state from conducting (with Idss flow) to cutoff (with Idss eliminated). This parameter change enables complete current suppression without altering the power supply configuration, thus extending talk time while maintaining operational simplicity.
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
The solution effectively suppresses power consumption by preventing wasteful current flow and increasing power gain, enabling longer talk times and more efficient operation in fifth-generation communication devices.
Implementation Method 1
an initial-stage amplifier circuit including a first high electron mobility transistor having a source electrically connected to a reference potential, and a gate to which a radio-frequency input signal is inputted, and a first heterojunction bipolar transistor having an emitter electrically connected to a drain of the first high electron mobility transistor
Implementation Method 2
an output-stage amplifier circuit including a second heterojunction bipolar transistor having an emitter electrically connected to the reference potential, a base to which the radio-frequency signal outputted from the first heterojunction bipolar transistor is inputted, and a collector to which direct-current power is supplied and from which a radio-frequency output signal is outputted
Data Source
AI summary
A power amplifier includes initial-stage and output-stage amplifier circuits, and initial-stage and output-stage bias circuits. The initial-stage amplifier circuit includes a first high electron mobility transistor having a source electrically connected to a reference potential, and a gate to which a radio-frequency input signal is inputted, and a first heterojunction bipolar transistor having an emitter electrically connected to a drain of the first high electron mobility transistor, a base electrically connected to the reference potential in an alternate-current fashion, and a collector to which direct-current power is supplied and from which a radio-frequency signal is outputted. The output-stage amplifier circuit includes a second heterojunction bipolar transistor having an emitter electrically connected to the reference potential, a base to which the radio-frequency signal outputted from the first heterojunction bipolar transistor is inputted, and a collector to which direct-current power is supplied and from which a radio-frequency output signal is outputted.