Schottky Bias Circuit for Low-Voltage RF Leakage Compensation

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Solution Overview

Problem

Bias circuits for power amplifiers face performance degradation due to RF energy leakage, which affects the bias voltage and gain, especially when operating at lower voltage supplies, limiting the efficiency and bandwidth of the amplifier.

Innovation Solution

The use of a bias circuit design incorporating a Schottky diode and a common-drain amplifier, along with a frequency compensation RC circuit, allows the bias circuit to operate at lower voltages (e.g., 2.5 volts or less) while maintaining performance by rectifying RF energy and stabilizing the feedback loop, thereby reducing the required power supply voltage and increasing battery life.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a bias circuit is used to set operating voltage for power amplifier, then the power amplifier can operate, but RF energy leaks onto the bias circuit line causing bias shift and performance degradation

Engineering Contradiction:

Improvebias circuit performanceVSAvoidRF energy leakage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The Schottky diode captures the harmful RF energy that leaks onto the bias circuit and rectifies it to generate additional bias voltage. This converts the previously harmful RF interference into a useful signal that enhances the bias voltage, compensating for voltage drops and maintaining stable operation of the power amplifier.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The Schottky diode acts as an intermediary element between the RF signal path and the bias circuit. It selectively interacts with RF energy on the bias line, rectifying it to DC voltage while allowing the bias circuit to continue its normal function of setting the operating point for the power amplifier.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Duration of action of moving object

If operating voltage is reduced to save power, then battery life increases, but bias circuit performance degrades due to insufficient voltage headroom

Engineering Contradiction:

Improvebattery lifeVSAvoidbias circuit performance

Core Design Contradiction:

Duration of action of moving objectVSReliability

Solution Approach 1:

By rectifying RF energy present on the bias circuit line, the Schottky diode generates additional voltage that compensates for the low supply voltage. This allows the bias circuit to maintain proper operating levels even when powered from low-voltage batteries, enabling extended battery life without sacrificing performance.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The circuit changes the voltage parameter by adding rectified RF voltage to the bias circuit supply. This dynamic voltage supplementation allows the circuit to operate reliably at lower nominal supply voltages, effectively extending battery life while maintaining performance through the added voltage from RF rectification.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If wide bandwidth biasing is implemented, then the bias circuit can operate across frequency ranges, but RF energy leakage affects broader frequency spectrum causing more significant performance degradation

Engineering Contradiction:

Improvebias bandwidthVSAvoidRF energy leakage across frequencies

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The Schottky diode's broad frequency response allows it to capture and rectify RF energy across a wide frequency spectrum. This converts harmful RF leakage across multiple frequencies into useful DC voltage, maintaining bias stability for wideband power amplifier operation while simultaneously mitigating the harmful effects of RF interference across the entire operating bandwidth.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 solution effectively reduces the required battery voltage, enhances battery life, and maintains the rectification effect and wide bandwidth of the bias circuit, improving the power amplifier's efficiency and performance even at lower voltage supplies.

Implementation Method 1

a Schottky diode configured to receive a bias signal and a radio frequency (RF) signal and generate a rectified signal

Methodology Applied

Scientific EffectRectification: Diode

Data Source

PatentUS10320334B2Schottky enhanced bias circuit

Publication Date: 2019.06.11 SKYWORKS SOLUTIONS INC

AI summary

Embodiments disclosed herein relate to a bias circuit that uses Schottky diodes. Typically, a bias circuit will include a number of transistors used to generate a bias voltage or a bias current for a power amplifier. Many wireless devices include power amplifiers to facilitate processing signals for transmission and/or received signals. By substituting the bias circuit design with a design that utilizes Schottky diodes, the required battery voltage of the bias circuit may be reduced enabling the use of lower voltage power supplies.