Patent limitations

Thread Starter


Joined Jan 10, 2012
Hello I'm new here. I have a question about patents.

Let's take a 2 different audio amplifiers for example. They both do the same job, and so you would assume that the circuitry is about 75% the same. There are only so many ways to configure a clean gain stage.

How different of an amplifier most you design for it not to be under someone else patent? Sorry if my question isn't clear. I'm designing something and when I see similar schematics, there are just parts to the circuit which can't be different without being ridiculous about it. (like changing a 10ohm with two 20's in parallel)


Joined Feb 19, 2009
This is something you essentially need a patent lawyer to look at for you if you are going into mass production.

If you plan to build a one off, not for profit, you are free to copy the exact circuit from the patent to see how it works, if it works good, you can keep it. You can even make another for yourself. You can't build any to sell.

Patents are an Excellent source for learning some good engineering practices. There are also a lot which are horrible examples. Stick with patents from well known companies for circuits to build.

A patent is only a piece of paper that gives the inventor the right to sue, so if you are looking to file a patent, unless you plan to make roughly $500,000/year from the design, do not patent it. Simply produce and keep the design proprietary. No matter what, somebody is simply going to copy the design to sell anyway, such as overseas fab shops, which don't need to obey the US Patent Office.


Joined Dec 26, 2010
Many basic configurations will be in the public domain. Some particular circuit inventions will be covered by patents or copyrights. If you really want to know what's what to avoid legal issues, you will require expert advice.

This applies particularly if you are deliberately basing a design on information obtained from existing products.


Joined Mar 24, 2008
Patents are a frequent subject of discussion in the off topic area. The general consensus is pretty much what TOG said in post #2. Basically our system is broken, and when taken in context with the global economy, is irrelevant.


Joined Oct 26, 2011
You are talking about a Nuts and Bolts type patent in which the circuit becomes intellectual property and cannot be copied exactly--changing a relatively small detail gets around this--your example probably would be an infringement. This type of patent is not very valuable, but tends to scare away garage shop operations that might make copies. Litigation is very rare in such cases.

A better and cheaper method to protect intellectual property is to grind part numbers off the ICs etc--anyone that can figure out which ICs are being used has the expertise to design his own product.

If you are concerned about patent infringement in a specific circuit, simply read the patent--in many cases, it is merely a bluff with no legitimate claims.

The other case is "Patent Applied For" which may or may not have any teeth--usually not because many applications are not followed up after application just so the product can be labeled so--they are really unpatentable

A patent becomes much broader and more valuable if legitimate claims are made about circuit techniques and topologies that have not been used before--these cannot be copied even with minor changes.

My advise--don't worry about infringement as amplifiers are so ubiquitous and diverse that nobody is checking or even cares about such stuff. Consider the difficulties involved:

1. Is the schematic published? if not, who is going to bother trace out the circuit to get it?

2. Does your product serious compete with the big guys? if not, there is no financial incentive go go after the competition

3. Is anyone going to notice? there is so much stuff out there already that the little operations are almost invisible

4. Litigation is very expensive and starts with a demand letter--if it ever comes to this point (very unlikely) all that has to be done is to comply with the demand and stop manufacture

5. Litigation is risky for the patent owner--up to this point nobody has proven or really cares that the claims are accurate--yes, the patent office has rules and procedures, but many patents are problematic--the claims must now be proven in a court of law--something that is generally avoided

6. Patents expire and become public domain--toward the end of their lives, they cease to be as valuable

For instance, output stages use push-pull, complementary symmetry, quasi complementary symmetry, totem pole, and bootstrap topologies--these are now all public domain--where you could run into problems is copying and large scale manufacture using the most recent Class D topologies.


Joined May 11, 2009
A patent protect (sort of) others from using a invention in a comercial setting. In a non comerecial setting. Then you as hobbyist buildin an amplifier for your self. You are free to do as you want.
Then an invention is granted a patent. The invention will also be public for evryone to read about it. And it is no law that keep others from discussing it in a forum like this. So it is no need to be cryptic. Just tell us what you want to do


Joined Apr 16, 2010
And the irony is that there are now companies who do nothing but buy intellectual property (patents), and use them to bully anyone and everyone who has money and a product that might infringe on "their property." Most defendents don't have the will and/or the resources to fight it out, and end up capitulating to these immoral moneygrubbers.


Joined Jun 6, 2011
How different of an amplifier most you design for it not to be under someone else patent?
As mentioned above, a patent attorney helps, but is not always necessary. If you have a copy of the patent in question, do the following:

1. Ignore the "specification". This is the descriptive part of the patent that talks about the invention and various embodiments of it. Its purpose is only to support the "claims", protect the inventor from others who may try to patent an extension of his ideas, and disclose additional concepts that may be covered later under a "divisional" application. It has no legal standing with respect to what concepts the patent covers.

2. Pay close attention to the claims, especially "independent" claims. These are the claims that are not dependent on other claims in the patent. You can tell the difference because dependent claims refer to previous claims.

3. For each independent claim, make a check list, where each item represents each individual aspect of the claim.

4. Compare each item on the checklist to your design. Check off those that that cover an element of your design.

5. If you check off all of the items on any one independent claim, then you probably infringe. If no one claim is entirely checked off, then you probably do not infringe.

6. If you intend to make lots of money off your idea, and keep it, pay an attorney for his opinion. You can save lots on attorney's fees if you do the previous homework first! (provide the attorney with your analysis).

There are some who believe that trying to determine infringement is a bad idea, whether by yourself or through an attorney.

This is because, if you are sued, and you had prior knowledge of the particular patent, you could be found to have "willfully" infringed the patent. The damages for willful infringement are significantly more painful than unintentional infringement.

Note: I am *not* an attorney, and I am *not* providing legal advise. Just IMHO!


Joined Jun 7, 2009
you'll find most patents today revolve around the deployment of some new technology. The basic circuits are public domain. Applying them in unique ways, could be patentable to protect a commercial enterprise. If your idea came about because of someone else's idea, it's best to do research on the legal ramifications. The other approach is to house public domain in a sealed black box, but an identifiable name/logo on it, and copyright.

Thread Starter


Joined Jan 10, 2012
Thanks for the wealth of information! And thanks for the pdf link.

I'll be browsing the forums, to try and give back some knowledge.


Joined Feb 24, 2006
If you are an inventor, the very last thing you want to do is behave like one. There is nobody out there who will ever hand you a pile of cash for an idea. It is far more cost effective to infringe and dare you to sue. You have to start a business to commercialize the idea and when the copycats show up you have to move on to the next NEW-NEW thing. Short and simple wins the day. One single isolated idea won't make you rich. One hundred ideas, one of which is profitable will however lead to a wealth increase.


Joined Oct 2, 2009
It is very unlikely that you can obtain a patent for an electronic circuit. Any "knowledgeable practitioner in the field" (which includes many here on AAC) would be able to arrive at the identical circuit in the normal course of pursuit.

Secondly, a patent application must reveal fully all components, procedures and processes in the proposed patent. Once your patent is made public, the whole world knows about it and someone is likely to copy it. A patent does not prevent others from stealing your idea.

The patent gives you the opportunity to spend all your life-savings in suing someone for possible patent infringement, which you will probably lose anyway.