EXHIBIT 5

                AMENDMENT NO. 2 TO AGREEMENT AND PLAN OF MERGER

          This AMENDMENT NO. 2 TO AGREEMENT AND PLAN OF MERGER (this
"Amendment"), dated as of January 4, 1999, is entered into by and among
Quickturn Design Systems, Inc., a Delaware corporation (the "Company"), Cadence
Design Systems, Inc., a Delaware corporation ("Parent"), and CDSI Acquisition,
Inc., a Delaware corporation and a wholly owned subsidiary of Parent
("Acquisition").  Capitalized terms used herein but not defined herein shall
have the meanings set forth in the Merger Agreement (defined below).

          WHEREAS, (i) the Company, Parent and Acquisition have previously
entered into that certain Agreement and Plan of Merger, dated as of December 8,
1998, as amended by Amendment No. 1 to Agreement and Plan of Merger, dated as of
December 16, 1998 (the "Merger Agreement"), and (ii) the Company, Parent and
Acquisition have determined that it is advisable to amend the terms of the
Merger Agreement.

          NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, and intending to be legally bound
hereby, the Company, Parent and Acquisition hereby agree as follows:

                                   ARTICLE 1

                      AMENDMENTS TO THE MERGER AGREEMENT

          1.1.  Section 1.8(b) of the Merger Agreement is hereby amended and
restated to read in its entirety as follows:

     "(b) The Exchange Ratio shall be (i) $15.00 divided by (ii) the average
     closing price of one share of Parent Common Stock (as reported on the NYSE
     Composite Transactions reporting system) during the five trading days
     immediately preceding the second business day prior to the Closing Date."

                                   ARTICLE 2

                                 MISCELLANEOUS

          2.1.  Affirmation.  All terms of the Merger Agreement not expressly
                ------------                                                 
amended in this Amendment remain unmodified and in full force and effect.

          2.2.  Entire Agreement.  The Merger Agreement, as amended by this
                ----------------                                           
Amendment (including the Company Disclosure Schedule), constitutes the entire
agreement among the parties hereto with respect to the subject matter hereof and
supersedes all other

 
prior agreements and understandings both written and oral between the parties
with respect to the subject matter hereof.

          2.3.  Validity.  If any provision of this Amendment or the Merger
                --------                                                   
Agreement, the application thereof to any person or circumstance is held invalid
or unenforceable, the remainder of this Amendment and the Merger Agreement and
the application of such provision to other persons or circumstances shall not be
affected thereby and to such end the provisions of this Amendment and the Merger
Agreement are agreed to be severable.

          2.4.  Governing Law.  This Amendment shall be governed by and
                -------------                                          
construed in accordance with the laws of the State of Delaware without regard to
the principles of conflicts of law thereof.

          2.5.  Descriptive Headings.  The descriptive headings herein are
                --------------------                                      
inserted for convenience of reference only and are not intended to be part of or
to affect the meaning or interpretation of this Amendment.

          2.6.  Personal Liability.  This Amendment shall not create or be
                ------------------                                        
deemed to create or permit any personal liability or obligation on the part of
any direct or indirect stockholder of the Company or Parent or Acquisition or
any officer, director, employee, agent, representative or investor of any party
hereto.

          2.7.  Counterparts.  This Amendment may be executed in one or more
                ------------                                                
counterparts, each of which shall be deemed to be an original but all of which
shall constitute one and the same agreement.

                 (Remainder of page intentionally left blank)

 
          IN WITNESS WHEREOF, each of the parties has caused this Amendment to
be duly executed on its behalf as of the day and year first above written.
                                 CADENCE DESIGN SYSTEMS, INC.
 
                                 By:   /s/H. Raymond Bingham
                                     -----------------------
                                 Name:    H. Raymond Bingham
                                 Title:   Executive Vice President and
                                          Chief Financial Officer


                                 QUICKTURN DESIGN SYSTEMS, INC.
 
                                 By:    /s/Keith R. Lobo
                                     -----------------------
                                 Name:    Keith R. Lobo
                                 Title:   President and Chief Executive Officer


                                 CDSI ACQUISITION, INC.
 
                                 By:    /s/H. Raymond Bingham
                                     ------------------------
                                 Name:    H. Raymond Bingham
                                 Title:   Executive Vice President and
                                          Chief Financial Officer