Synopsys, Inc. v. Real Intent, Inc.

Background

Synopsys sued Real Intent for allegedly infringing U.S. Patent No. 9,721,057, which concerns a system and method for verifying clock domain crossings in chip designs. Synopsys also alleged that Real Intent improperly copied copyrighted expression and integrated-circuit designs, although this order addresses claim construction for the patent claims.

Clock domain crossing verification examines signals moving between parts of a circuit that operate under different clocks. The patent describes an automated process for carrying clock-domain-crossing constraints from the register-transfer level of a chip design to the later netlist level. The parties disputed the meaning of eight terms in the patent claims.

Request to Strike Expert Evidence

Real Intent asked the court to strike the report and declaration of Synopsys’s expert, Dr. Baris Taskin. Real Intent argued that the declaration was an untimely supplemental expert report and that Dr. Taskin’s opinions were unreliable because he adopted constructions prepared by Synopsys’s attorneys and did not consider extrinsic evidence.

The court denied the request to strike. It found that Dr. Taskin’s original report was timely, Real Intent had deposed him before the claim-construction hearing, and the short declaration summarized portions of his deposition. The court also found no showing of prejudice from the alleged delay. It treated Real Intent’s other challenges as going to the weight of the report rather than its admissibility.

Claim Constructions

The court construed the disputed terms as follows:

1. “Clock domain crossing” or “CDC.” The court adopted Real Intent’s construction: “the sending and receiving of signals between at least two sections of a circuit design driven by different clocks.” The court rejected Synopsys’s proposal because clock-domain crossings can be either synchronous or asynchronous; they are not limited to crossings involving asynchronous clocks.

2. “Asynchronous clock domain crossings.” The court rejected both parties’ proposed constructions and defined the term as “clock domain crossings between clocks with a variable phase relationship.” The court explained that “asynchronous” describes the relationship between clocks, while “unsynchronized” concerns whether synchronization mechanisms are being used. An asynchronous crossing can therefore be synchronized.

3. “Register transfer-level” or “RTL” design. The court adopted Synopsys’s proposal with an addition, defining the term as a “description of a digital electronic circuit at the register level written in a behavioral hardware design language such as Verilog or VHDL.” The added phrase “at the register level” distinguishes RTL design from the later netlist stage.

4. “RTL-level CDC constraints.” The court adopted Synopsys’s construction: “one or more limits on parameter values for a clock signal identified by its RTL-level name.” The court declined to add references to blocks and paths because it understood those as separate exclusion constraints rather than part of the definition of CDC constraints.

5. “Netlist CDC constraints.” The court adopted Synopsys’s construction: “one or more limits on parameter values for a clock signal identified by its gate-level netlist name.”

6. “Migrating” or “migrate” RTL-level CDC constraints to netlist CDC constraints. The court adopted Synopsys’s construction: “creating netlist CDC constraints from RTL-level CDC constraints.” It declined to require that the process use signal-mapping heuristics or operate on the received RTL design. The court found that the patent describes heuristics as an example rather than a required technique, and that the mapping is applied to signal names rather than to the design as a whole.

7. “Identify correspondences between RTL and netlist level crossings.” The court found that no special construction was necessary and applied the term’s plain and ordinary meaning. It rejected Real Intent’s position that corresponding crossings must be equivalent, reasoning that the patent allows corresponding items to have differences.

8. “Previously provided by a user for sign-off.” The court also found that no special construction was necessary and applied the term’s plain and ordinary meaning. The court rejected Real Intent’s position that sign-off makes the constraints permanently final. The patent describes an iterative design process in which later findings can lead to changes at the RTL stage.

Disposition

The court denied Real Intent’s request to strike Dr. Taskin’s report and declaration. It construed the eight disputed terms as described above and ordered that the claim-construction rulings govern the patent litigation. The order was signed by Judge Edward J. Davila.