Cascode Power Amplifier Feedback for Noise-Suppressed Output Control
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Solution Overview
Problem
Existing power amplifier circuits in mobile communication devices experience noise interference due to cascode configurations, which can deteriorate receiving sensitivity by mixing noise into the transmission signal and causing output power fluctuations.
Innovation Solution
A power amplifier circuit design incorporating a first transistor, a bias circuit, a second transistor, and feedback circuits to control the gain and suppress noise, where the second transistor is cascode-connected to the first transistor, and feedback circuits are used to reduce the gain of the upper-stage transistor, thereby minimizing noise amplification and maintaining stable output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a cascode configuration is used to suppress output power fluctuations, then output power stability is improved, but noise is mixed into the transmission signal and receiving sensitivity deteriorates
Solution Approach 1:
The patent introduces a feedback circuit connected between the collector of the upper-stage transistor and the base of the lower-stage transistor. This feedback circuit includes a capacitor and resistor that form a noise filter, which selectively feeds back signals while filtering out noise components. The feedback mechanism stabilizes the operating point and reduces noise mixing by compensating for variations in the cascode configuration.
Solution Approach 2:
The patent introduces an intermediate feedback network between the upper and lower stage transistors. This intermediary circuit includes capacitive and resistive elements that mediate the interaction between stages, allowing signal transmission while blocking noise. The intermediary feedback path provides a controlled coupling that prevents direct noise transfer while maintaining the cascode stability benefit.
2Ease of operation
If an additional transistor is cascode-connected to control collector current changes, then output power control is improved, but device complexity increases
Solution Approach 1:
The upper-stage transistor in the cascode configuration serves multiple functions: it controls the collector current of the lower stage, provides output impedance, and participates in the feedback mechanism. By making the transistor multi-functional, the patent reduces the need for additional separate control circuits, thereby managing device complexity while maintaining ease of operation.
Solution Approach 2:
The feedback circuit provides automatic control of the lower-stage transistor's base current based on the upper-stage transistor's collector voltage. This feedback mechanism enables easy output power control through a single control voltage applied to the upper-stage transistor base, eliminating the need for complex external control circuits.
3Object-affected harmful factors
If feedback circuit is added to reduce upper-stage transistor gain, then noise amplification is suppressed, but device complexity increases
Solution Approach 1:
The feedback circuit changes the effective gain parameter of the upper-stage transistor by introducing a feedback path. The capacitive and resistive elements in the feedback circuit create a frequency-dependent feedback factor that reduces the gain at noise frequencies while maintaining signal amplification. This parameter change approach suppresses noise amplification using simple passive components rather than complex active control circuits.
Data Source
AI summary
The present disclosure provides a power amplifier circuit capable of suppressing the occurrence of noises while enabling control of an output power level. The power amplifier circuit includes a first transistor that amplifies a first signal; a bias circuit that supplies a bias current or voltage based on a control signal to the first transistor; a second transistor to which a control current based on the control signal is supplied, which has an emitter or a source thereof connected to a collector or a drain of the first transistor, and from which a second signal obtained by amplifying the first signal is output; and a first feedback circuit provided between the collector or the drain of the second transistor and the base or the gate of the second transistor.