How a Radio Amplifier Saves Energy by Sharing Work
This patent describes a power amplifier design that dynamically adjusts the power supplied to two amplifier stages based on the strength of the incoming radio signal, making it more efficient.
Original patent title: “Bias circuit for a power amplifier”
This patent describes a power amplifier design that dynamically adjusts the power supplied to two amplifier stages based on the strength of the incoming radio signal, making it more efficient. Granted to Motorola in 1998 with 11 claims and 94 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
This patent describes a power amplifier that improves efficiency by dynamically adjusting how two internal amplifiers operate. It starts by splitting an incoming radio frequency (RF) signal into two parts: an "in-phase" signal and a "quadrature phase" signal using a power divider (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 1). A "carrier amplifier" boosts the in-phase signal, and a "peaking amplifier" boosts the quadrature phase signal (Claim 1). The clever part is how the power supplied to these amplifiers (their "bias inputs") is controlled. As the strength of the incoming RF signal changes, the bias to the carrier amplifier decreases while the bias to the peaking amplifier increases (Claim 1). This ensures that the amplifiers only work as hard as needed, saving energy. Finally, the boosted signals are combined to create the strong output signal (Claim 1). For example, when a cell phone transmits a weak signal, the carrier amplifier might handle most of the work, but for a strong signal, the peaking amplifier kicks in more to help.
The gap
What does this patent NOT cover?
- Does not cover power amplifiers that use only a single amplifier stage.
- Does not cover power amplifiers where the bias inputs for the carrier and peaking amplifiers are fixed or adjusted independently without the inverse relationship described (carrier bias decreases as peaking bias increases).
- Does not cover power amplifiers that split the RF input signal into more than two components (in-phase and quadrature phase).
- Does not cover power amplifiers where the bias control signals are not derived from the magnitude of the RF input signal or the current drawn by the carrier amplifier.
- Does not cover power amplifiers where the two amplified signals are not combined in additive phase.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The innovation lies in dynamically and inversely controlling the power (bias) to two separate amplifier stages based on the incoming signal's strength. This allows one amplifier to handle low-power signals efficiently, while the other steps in to provide additional power only when needed for stronger signals, preventing wasted energy.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Cellular base station power amplifiers
Smartphone radio frequency front-ends
Wi-Fi access point transmitters
Satellite communication transceivers
Broadcast radio and TV transmitters
Why it matters
The bigger picture
Efficient power amplifiers are crucial for any device that transmits radio signals, like cell phones, Wi-Fi routers, and broadcast equipment. They consume a significant portion of a device's power, so improving their efficiency directly translates to longer battery life for mobile devices and reduced energy consumption for base stations. This patent describes a technique to achieve higher efficiency, especially when the signal strength varies, which is common in wireless communication.
Filed
June 28, 1996
Granted
May 26, 1998
Market context
Who's building on this
Companies in this space
Companies like Qualcomm, Broadcom, Qorvo, and Skyworks Solutions are continuously developing highly efficient power amplifiers for cellular, Wi-Fi, and other wireless communication standards. These companies integrate advanced biasing techniques, including those similar to the Doherty amplifier principle this patent describes, into their RF front-end modules for smartphones and base stations.
Market impact
This type of efficiency-enhancing technology for power amplifiers has been fundamental in the evolution of wireless communication. It enabled longer battery life in mobile devices and reduced operational costs for cellular network providers by making their base stations more energy-efficient. It became a standard approach for designing power amplifiers that need to handle signals with varying power levels, which is typical for modern modulated signals.
Claim 1 — Plain English
What this patent covers
This patent describes a power amplifier that improves efficiency by dynamically adjusting how two internal amplifiers operate. It starts by splitting an incoming radio frequency (RF) signal into two parts: an "in-phase" signal and a "quadrature phase" signal using a power divider (Claim 1). A "carrier amplifier" boosts the in-phase signal, and a "peaking amplifier" boosts the quadrature phase signal (Claim 1). The clever part is how the power supplied to these amplifiers (their "bias inputs") is controlled. As the strength of the incoming RF signal changes, the bias to the carrier amplifier decreases while the bias to the peaking amplifier increases (Claim 1). This ensures that the amplifiers only work as hard as needed, saving energy. Finally, the boosted signals are combined to create the strong output signal (Claim 1). For example, when a cell phone transmits a weak signal, the carrier amplifier might handle most of the work, but for a strong signal, the peaking amplifier kicks in more to help.
The clever bit
The innovation lies in dynamically and inversely controlling the power (bias) to two separate amplifier stages based on the incoming signal's strength. This allows one amplifier to handle low-power signals efficiently, while the other steps in to provide additional power only when needed for stronger signals, preventing wasted energy.
What it does not cover
- Does not cover power amplifiers that use only a single amplifier stage.
- Does not cover power amplifiers where the bias inputs for the carrier and peaking amplifiers are fixed or adjusted independently without the inverse relationship described (carrier bias decreases as peaking bias increases).
- Does not cover power amplifiers that split the RF input signal into more than two components (in-phase and quadrature phase).
- Does not cover power amplifiers where the bias control signals are not derived from the magnitude of the RF input signal or the current drawn by the carrier amplifier.
- Does not cover power amplifiers where the two amplified signals are not combined in additive phase.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Strong
Citation count
39/40
Highly cited
Claim breadth
7/20
Moderate scope
Recency
0/20
Older than 20 years
Assignee scale
20/20
Major company or institution
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$32K – $101K
Midpoint $63K · expired or expiring · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
The original legal language
Original claims
11 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Mitzlaff, J. E. (1998). How a Radio Amplifier Saves Energy by Sharing Work (U.S. Patent No. 5,757,229). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/5757229/bias-circuit-for-a-power-amplifier
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How a Radio Amplifier Saves Energy by Sharing Work cover?
This patent describes a power amplifier design that dynamically adjusts the power supplied to two amplifier stages based on the strength of the incoming radio signal, making it more efficient.
Who owns patent US 5757229?
Motorola owns this patent, granted in 1998.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 5757229 cited by?
This patent has been cited by 94 later patents that build on its ideas.
What problem does this patent solve?
Efficient power amplifiers are crucial for any device that transmits radio signals, like cell phones, Wi-Fi routers, and broadcast equipment. They consume a significant portion of a device's power, so improving their efficiency directly translates to longer battery life for mobile devices and reduced energy consumption for base stations. This patent describes a technique to achieve higher efficiency, especially when the signal strength varies, which is common in wireless communication.
What does this patent NOT cover?
Does not cover power amplifiers that use only a single amplifier stage.
Patent monitoring