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Patent Claim Interpretation for Infringement Purposes

Posted Thursday, September 27, 2012 by Mike Cicero

Generally, a patent owner’s exclusive rights are violated when another entity infringes on those rights and, as a result, the infringing entity might be liable to the patent owner for monetary damages. This may seem straight forward, but determining whether patent infringement has occurred requires determining whether someone has, without authority, made, used, offered to sell, or sold the patented invention, within the United States, during the term of the patent. 35 U.S.C. §271(a). Because the claims of a patent define the owner’s exclusive rights, it is necessary to perform patent claim interpretation in order to determine exactly what the patented invention is.

In order to perform patent claim interpretation, Federal Courts conduct, prior to trial, what have come to be known as “Markman hearings” during which a judge, based on evidence provided by both parties, issues an order that construes the claims. The claim construction takes place prior to the hearing because in Markman v. Westview Instruments, Inc., the Supreme Court ruled that claim construction was purely a question of law and, therefore, could not be conducted by the jury, the sole purpose of which is finder of fact. 517 U.S. 370 (1996). The claim construction issued by the judge after a Markman hearing becomes the basis for determining, at the trial, whether the patented invention has been infringed upon.

During the Markman hearing, there exists at least a general methodology for applying the evidence provided to construe the claims. The judge first considers any intrinsic evidence, evidence that is directly related to the patent, to determine the meaning and scope of the claims. Intrinsic evidence includes the patent specification, including the actual patent claims, as well as the patent’s prosecution history. In some cases, extrinsic evidence is considered; however, the consideration of extrinsic evidence is limited. Examples of extrinsic evidence might include dictionaries, treatise, expert testimony, and possibly even other unrelated patent documents.

Within the intrinsic evidence category, a judge will typically first look to the claim at issue and the other claims in the patent and employ claim differentiation. Essentially, the Doctrine of Claim Differentiation assumes that an applicant would not have drafted two claims using different language with the intention that the claims are identical in scope and meaning. As such, the court should not apply an identical meaning to different patent claims. For example, if independent claim 1 comprises limitations A, B, and C, and dependent claim 2 comprises limitations A, B, C, and D, then it would be improper for the court to read limitation D into claim 1. (For more on this see Doctrine of Claim Differentiation).

Also included within the category of intrinsic evidence is the patent specification as a whole and the prosecution history or image file wrapper. Even though it is the claims, and nothing else, that define the scope of the patent’s protection, the claims are to be interpreted in light of the specification and prosecution history to resolve issues of ambiguity or indefiniteness.

The specification is a natural choice of sources of information to gain an understanding of the claims. If fact, the patent applicant even possesses the ability to act as her own lexicographer, which means she can use the specification to define terms as she chooses, so long as she doesn’t provide a definition that is confusing, inconsistent, or simply incorrect. For example, an applicant could provide a definition for a term which has multiple common usage meanings if she intends for only one of the common usage meanings to control the claims. In the order issued from a Markman hearing the judge would most likely import the defined meaning into the claims to limit the scope of the patented invention.

Prosecution history is another good source of intrinsic evidence. A prime example is that the prosecution history is commonly looked to for evidence to invoke the doctrine of prosecution history estoppel. Essentially, this doctrine provides that when an applicant narrows her claims by an amendment during prosecution of the patent in order to work around the cited prior art and overcome a rejection, she is later estopped from invoking the doctrine of equivalents to broaden the scope of her protection. (For more on this see Doctrine of Equivalents).

Extrinsic evidence is not offered in every case but may include, for example, expert testimony tending to establish, for example, what a term in a claim meant to a person of ordinary skill in the art at the time the invention was made.

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