Sliding Bias Controller for RF Power Amplifier Efficiency

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Solution Overview

Problem

RF power amplifiers face inefficiencies due to high quiescent current consumption at lower power output levels, which increases DC power consumption and reduces amplifier efficiency, especially when using diode-based detectors that suffer from delay and small signal level issues.

Innovation Solution

A two-stage power amplifier circuit employing a sliding bias controller to reduce bias currents at lower power output levels, combined with a controllable DC to DC converter to optimize supply voltage, thereby improving efficiency by operating at Class B at lower levels and Class AB at higher levels, without the need for extra reference generators or calibration time.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If bias current is maintained at nominal levels to ensure adequate operation, then amplifier linearity and reliability are improved, but quiescent current consumption increases and efficiency deteriorates at lower power output levels

Engineering Contradiction:

Improveamplifier operation reliabilityVSAvoidquiescent current consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The bias controller dynamically adjusts the bias current based on the power output level. At lower power output levels, the bias current is reduced from nominal levels to decrease quiescent current consumption. At higher power output levels, the bias current is maintained at nominal levels to ensure adequate amplifier operation and linearity. This dynamic adjustment resolves the contradiction between reliability and energy consumption.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the bias current parameter according to the operating conditions. By detecting the power output level and相应地 adjusting the bias current, the system optimizes the trade-off between amplifier performance and power consumption. The bias current transitions from a fixed nominal value to a variable parameter that adapts to different operating points.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If bias current is reduced at lower power output levels to improve efficiency, then power consumption decreases, but amplifier linearity and operation reliability may deteriorate

Engineering Contradiction:

Improvepower consumptionVSAvoidamplifier linearity

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The bias controller implements dynamic bias current adjustment that is contingent on the power output level. The system maintains nominal bias current at higher power levels where linearity is critical, and reduces bias current only at lower power levels where the amplifier can operate with reduced current while maintaining adequate linearity. This conditional dynamic adjustment resolves the contradiction between power consumption and linearity.

Inventive Principle:

Principle #15Dynamics

3Device complexity

If diode-based detectors are used to detect RF signal magnitude, then device complexity is reduced, but delay and small signal level detection issues arise

Engineering Contradiction:

Improvedetector circuit complexityVSAvoiddetection delay

Core Design Contradiction:

Device complexityVSLoss of time

Solution Approach 1:

The invention replaces diode-based detection with a transimpedance amplifier-based detection system. The transimpedance amplifier converts the RF signal current directly to voltage with high bandwidth and no inherent delay, eliminating the detection delay and small signal level issues associated with diode-based detectors. This substitution resolves the contradiction between device complexity and detection performance.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS7315211B1Sliding bias controller for use with radio frequency power amplifiers

Publication Date: 2008.01.01 CANON KK

AI summary

A two stage power amplifier circuit that employs both a DC to DC converter and sliding bias controller to improve power amplifier efficiency. The control signal that is generated by the power detector circuit to control the input voltage to the DC to DC converter is also used to provide the reference voltage that controls the sliding bias controller. The sliding bias controller reduces the quiescent current of the power amplifiers by reducing the bias currents, and thus the DC voltage at lower power output levels driving the power amplifiers. This causes the power amplifiers to operate at or near higher efficiency Class B operation at lower power output levels. As the power level increases, the sliding bias controller reduces its control on the bias currents so that the power amplifier can be driven at necessary higher power output levels.