Envelope-Tracking Power Supply Circuit With Low-Parasitic Current Sensing
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Solution Overview
Problem
The tracking accuracy of power supply voltage with respect to the envelope of an RF signal is decreased due to parasitic capacitance and inductance in power supply paths and probes used in power amplifying modules employing the envelope tracking (ET) technique.
Innovation Solution
A power supply circuit that includes a transistor with a collector or drain connected to a fixed voltage source and a current detecting resistor between the fixed voltage source and the transistor, which reduces the influence of parasitic capacitance and inductance, allowing for accurate tracking of the envelope signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a probe is attached across a small resistance to monitor power supply current, then current monitoring is enabled, but parasitic capacitance and inductance decrease tracking accuracy
Solution Approach 1:
The patent extracts the harmful probe and its associated parasitic elements from the power supply path by using the transistor's built-in current detection capability. The emitter resistance serves as an intrinsic current sensing element that eliminates the need for external probes, thereby removing the source of parasitic capacitance and inductance that degraded tracking accuracy.
Solution Approach 2:
The patent introduces the transistor as an intermediary device between the power supply and the power amplifier. The transistor's emitter resistance acts as a built-in current sensor that provides accurate current information without requiring external probing, thus mediating the measurement process to avoid parasitic effects.
2Measurement precision
If a small resistance is provided in the power supply path, then current monitoring is possible, but voltage drop occurs
Solution Approach 1:
The patent changes the resistance value parameter to an extremely small level (0.01Ω or less) for the emitter resistance. This parameter optimization allows sufficient current monitoring capability while keeping the voltage drop negligible, thus resolving the contradiction between measurement precision and energy loss.
3Loss of energy
If envelope tracking is implemented to improve efficiency, then power loss is reduced, but tracking accuracy decreases due to parasitic elements
Solution Approach 1:
The patent removes the external probe from the system by utilizing the transistor's intrinsic emitter resistance for current sensing. This extraction of the harmful probing mechanism eliminates parasitic capacitance and inductance, thereby maintaining high tracking accuracy while preserving the power efficiency benefits of envelope tracking.
Solution Approach 2:
The transistor serves itself by using its own emitter resistance as the current sensing element. This self-service approach eliminates the need for external probing infrastructure, removing parasitic effects while maintaining the envelope tracking functionality and its associated power efficiency improvements.
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 configuration suppresses the decrease in tracking accuracy, particularly in high frequency bands, and broadens the frequency band supported by the ET technique.
Implementation Method 1
The transistor includes a collector or drain that is supplied with a voltage from a fixed voltage source, a base or gate that receives an envelope signal tracking an envelope of the RF signal, and an emitter or source that outputs the variable voltage that is based on the envelope signal
Implementation Method 2
The current detecting resistor is electrically connected between the fixed voltage source and the collector or drain of the transistor
Data Source
AI summary
A power supply circuit supplies a variable voltage to a power amplifier that amplifies a radio-frequency signal, and includes a transistor and a current detecting resistor. The transistor includes a collector or drain that is supplied with a fixed voltage from a fixed voltage source, a base or gate that receives an envelope signal tracking an envelope of the radio-frequency signal, and an emitter or source that outputs the variable voltage that is based on the envelope signal. The current detecting resistor is electrically connected between the fixed voltage source and the collector or drain of the transistor.