Intellectual property is an important intangible asset of today's enterprises. Among them, patent is the main tool for technology enterprises to keep their horses in the industry. The way of drafting claims will affect the quality of patents. The technical solution protected by claims is embodied in the technical features. Functional limitations are essential when defining the technical features of claims. Therefore, how to interpret the scope of the technical features of functional limitation in the phases of patent granting, litigation and infringement directly affects the scope of protection of the claims.

Through the analysis interpretation of functional technical features and their differences in the administrative and judicial organs of the patent granting, litigation and infringement of the three procedures between China and the United States, the suggestions is provided on the operation of functional technical features in practice.

Although our country has adopted inconsistent rules of interpretation in the stage of granting, litigation and infringement, it believes that such rules of interpretation are applicable to the existing drafting and examination. In the granting and invalidation procedure, we adopt the method of "covering all the implementations that can achieve the functions described" and the method of "concrete implementations and equivalent" in the tort procedure. In our judgment of functional limitation supported by description in practice, the examiner will determine all implementations. There is suggestion that introducing the method of determining equivalent of functional features into substantive examination so as to facilitate the examiner to prove that functional limitation include the embodiments of the disclosure and other equivalents realizing such function. The examiner needs to consider the equivalent of embodiments. The equivalents will be existing technology, equivalents of existing technology. Due to the examiner's personal subjective factors in the examination, it is recommended that the broadest reasonable interpretation will be adopted at the examination to ensure that the patent right is commensurate with the contribution made by the applicant.

At the same time, this paper argues that due to the particularity of functional features in infringement, it is necessary to distinguish equivalents of the functional features in the interpretation of infringement and the traditional equivalent principle under infringement. The scope of protection of functional features will be determined after the equivalent of embodiments. Because during the examination, the examiner will exam whether the functional limitation is supported by the description, therefore the description will disclose one or multiple embodiments. When defining the scope of claims, the equivalents of the embodiments of the description will be considered, but the equivalents of equivalents will not be considered. The equivalents of interpretation of the functional feature is realized based on the embodiments of the description. In the infringement procedure, the accused product and functional features need to be compared under literal infringement, the use of the method of two elements determine whether the accused product is the equivalent of the functional feature. The traditional doctrine of equivalents can be applied to the case where the literal infringement is not constituted.

The time point of judging the equivalents in the functional technical feature interpretation becomes the focus. The time point adopted by the U.S. Patent and Trademark Office for functional equivalence is the date of application, while the date adopted by the court in judging infringement is the granting publication date. At the examination, functional equivalence is considered primarily for creativity examination, and the cited references in the examination are all existing technologies, so functional equivalents are limited to the existing technologies and equivalents of the existing technology. For equivalents of the functional features are defined in the description, the functional features will be explained to the embodiments of the description and the described equivalents, and the equivalents will no longer consider the equivalents. The setting of the time node of the equivalents on the application day is beneficial to the maintenance of the public notification function of the patent system, while the setting of the time node on the granting date is beneficial to the protection of the interests of the patentee. Because of the inconsistency between the interpretation in the examination and that in the infringement stage, functional limitation equivalent does not appear in the examination but only in the infringement proceedings. In China's judicial interpretation, the time point is used on the date of application to identify the equivalents of functional limitation of technical features, while the time point of the principle of tort equivalence is on the date of infringement.

Identifying functional features is the basis of interpretation of the functional features. The 3-Prong Analysis of identifying functional features in the United States can be reference for China. Especially for the requirements of functional determinants, we can use the "structural" term of the United States to guide functional features.

The study of the interpretation of the functional technical features in the United States can provide a better understanding of the evolution and historical development of functional limits in the United States, especially the interpretation mechanism, the equivalents, the equivalents doctrine, the time points for determining equivalents,  and the method for determining functional limitation equivalents in substantive examination and infringement proceedings, and is conducive to understanding the meaning of functional features and the application of interpretation.

By comparing the complete process of functional features interpretation between China and the United States, this paper provides suggestions for the perfection of functional features interpretation rules in China, from the definition of functional features, the identification of functional features, the identification of equivalents of functional features in the substantive review, and the identification of the equivalents in infringement proceedings.