Direct-Coupled Push-Pull BJT Driver for RF Power Amplifier Bias

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Solution Overview

Problem

Current power amplifiers for cellular communication systems face challenges in achieving high output power, power added efficiency, and ruggedness due to the low voltage handling capability of CMOS transistors, which necessitates costly compound semiconductor processes and results in significant losses and complex design cycles.

Innovation Solution

A driver circuit with a programmable stage using CMOS technology, integrated with a high voltage handling GaAs or GaN output stage, providing dynamic DC bias and RF signal gain through a push-pull configuration with variable current sources and adjustable capacitors, eliminating the need for impedance transformation and enabling intrinsic short circuit protection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If CMOS transistors are used in power amplifiers to reduce cost, then manufacturing cost decreases, but voltage handling capability and output power are limited

Engineering Contradiction:

Improvemanufacturing costVSAvoidoutput power

Core Design Contradiction:

Ease of manufactureVSPower

Solution Approach 1:

The power amplifier is divided into two distinct stages: a CMOS driver stage for signal generation and a GaAs/GaN output stage for power amplification. This segmentation allows each stage to be optimized for its specific function, with the CMOS stage providing cost-effective signal processing and the GaAs/GaN stage delivering high voltage handling capability and output power.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs a hybrid architecture combining CMOS and GaAs/GaN technologies in a single power amplifier system. The CMOS driver stage utilizes standard semiconductor processes for cost-effectiveness, while the GaAs/GaN output stage leverages compound semiconductors for superior voltage and power handling, creating a composite system that balances cost and performance.

Inventive Principle:

Principle #40Composite materials

2Power

If GaAs compound semiconductor processes are used to achieve high output power, then power and efficiency improve, but manufacturing cost increases

Engineering Contradiction:

Improveoutput powerVSAvoidmanufacturing cost

Core Design Contradiction:

PowerVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Inventive Principle:

Principle #40Composite materials

3Stress or pressure

If transformers are used for impedance transformation in CMOS power amplifiers, then voltage handling is improved, but circuit losses and complexity increase

Engineering Contradiction:

Improvevoltage handling capabilityVSAvoidpower combining losses

Core Design Contradiction:

Stress or pressureVSLoss of energy

Solution Approach 1:

The patent eliminates transformers and power combining circuits from the amplifier architecture by using a direct coupled push-pull configuration. The differential to single-ended conversion is achieved through direct transistor coupling rather than magnetic components, removing the source of power losses and reducing overall circuit complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a direct coupled push-pull stage as an intermediary between the CMOS driver and the final output stage. This intermediate stage performs impedance transformation and voltage boosting through direct transistor coupling, eliminating the need for lossy transformers while maintaining voltage handling capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Loss of energy

If direct coupled push-pull configuration is used, then transformer losses are eliminated, but bias control and gain adjustment complexity increases

Engineering Contradiction:

Improvepower combining lossesVSAvoidbias circuitry complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The differential pair transistors in the push-pull stage serve multiple functions simultaneously: they provide impedance transformation, voltage boosting, and bias control. The current sources connected to the differential pair enable dynamic bias adjustment and gain control, consolidating multiple functions into a single circuit topology that reduces overall complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent employs variable current sources to dynamically adjust the bias conditions of the push-pull stage. By changing the current parameters, the circuit can control both the bias point and the gain of the amplifier, providing flexible control without requiring complex separate bias circuitry.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8497736B1Direct DC coupled push-pull BJT driver for power amplifier with built-in gain and bias current signal dependent expansion

Publication Date: 2013.07.30 SKYWORKS SOLUTIONS INC

AI summary

A power amplifier having a driver stage and an output stage is configured to provide an amplified RF input signal. The driver stage of the power amplifier consists of one or more driver circuits consisting of a network of transistors, current sources, capacitive elements and resistive elements. An RF input signal is fed into the driver stage which is configured to provide a dynamic DC bias and an RF signal gain to a base terminal of a Bipolar Junction Transistor (BJT) power device present in the output stage. The output stage includes of a network of transistors, capacitive and resistive elements and when driven by the DC bias and the RF signal from the driver stage produces an amplified RF input signal at an output side of the output stage.