Power Amplifier Bias Control Circuit for Stable RF Output Power

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Solution Overview

Problem

Radio frequency power amplifiers in GSM communication systems face issues with large chip area occupation, reduced maximum output power, and efficiency due to power transistors, and are prone to low frequency oscillations and spectral strays due to closed loop instability and transient response inconsistencies.

Innovation Solution

A power control circuit comprising a voltage-current converter, programmable current amplifier, waveform shaper, temperature compensator, and voltage compensator, which converts output power control signals into control currents and amplifies them as bias currents for the power amplifier, eliminating the need for a power transistor and creating an open-loop structure to improve stability and efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a power transistor is used in the voltage modulation circuit to control output power, then the output power can be controlled, but the chip area increases and power consumption increases

Engineering Contradiction:

Improveoutput power control capabilityVSAvoidchip area

Core Design Contradiction:

PowerVSArea of stationary object

Solution Approach 1:

The patent extracts and removes the power transistor from the voltage modulation circuit. Instead of using a power transistor to control output power, the invention uses a current amplifier to directly control the bias current of the power amplifier, thereby eliminating the need for a power transistor and reducing chip area occupation.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the voltage modulation mechanism (which requires a power transistor) with a current modulation mechanism. By using a current amplifier to directly control the bias current, the system substitutes the mechanical/voltage-based control with a current-based control system, achieving power control without the area penalty of a power transistor.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Power

If a power transistor is used in the voltage modulation circuit to control output power, then the output power can be controlled, but the maximum output power and efficiency are reduced

Engineering Contradiction:

Improveoutput power control capabilityVSAvoidpower consumption and efficiency

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Power

If a closed loop voltage modulation circuit is used to control power, then power control is achieved, but low frequency oscillation and spectral stray occur due to stability issues

Engineering Contradiction:

Improveoutput power control capabilityVSAvoidcircuit stability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Power

If a closed loop control is used to manage power amplifier output, then power control is achieved, but transient response speeds differ greatly and spectral stray occurs

Engineering Contradiction:

Improveoutput power control capabilityVSAvoidtransient response speed consistency

Core Design Contradiction:

PowerVSProductivity

Solution Approach 1:

The patent introduces a feedback mechanism where the output power control signal directly controls the bias current through the current amplifier. This feedback approach allows for consistent transient response across different power levels by directly adjusting the bias current based on the desired output power, eliminating the issues of inconsistent response speeds and spectral stray associated with closed-loop voltage modulation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS11177772B2Power control circuit and power amplification circuit

Publication Date: 2021.11.16 GUANGZHOU HUIZHI MICROELECTRONICS

AI summary

A power control circuit includes: a voltage-current converter and a programmable current amplifier; the voltage-current converter is configured to detect an inputted output power control signal, and to convert the output power control signal to a control current and output same; and the programmable current amplifier is configured to receive the control current and output the amplified control current as a bias current of the power amplifier connected to the power control circuit.