EXHIBIT 2
 
                        QUICKTURN DESIGN SYSTEMS, INC.

                                      AND

                               BANKBOSTON, N.A.
             (FORMERLY KNOWN AS THE FIRST NATIONAL BANK OF BOSTON)
                                 RIGHTS AGENT

                                AMENDMENT NO. 1
                                      TO
                       PREFERRED SHARES RIGHTS AGREEMENT


                          DATED AS OF AUGUST 25, 1998

 
                      AMENDMENT NO. 1 TO RIGHTS AGREEMENT


     Amendment No. 1 to Rights Agreement, dated as of August 25, 1998
("AMENDMENT NO. 1"), between Quickturn Design Systems, Inc., a Delaware
corporation (the "COMPANY"), and BankBoston, N.A. (formerly known as the First
National Bank of Boston) (the "RIGHTS AGENT").

     WHEREAS, on January 10, 1996 the Company and the Rights Agent entered into
a Rights Agreement (the "ORIGINAL AGREEMENT," as amended hereby is hereinafter
referred to as the "AGREEMENT");

     WHEREAS, the Company, with the approval of the Board of the Directors of
the Company, and the Rights Agent have mutually agreed to modify the terms of
the Agreement in certain respects pursuant to this Amendment No. 1.

     NOW, THEREFORE, in consideration of the promises and the mutual agreements
herein set forth, the parties hereto hereby agree that the Original Agreement is
amended as follows:

 1.  Amendment of "Certain Definitions" Section.
     ------------------------------------------ 

     (a) Section 1(g) of the Original Agreement is hereby deleted in its
entirety.

     (b) Section 1(h) of the Original Agreement is hereby deleted in its
entirety and the following is substituted therefore:

          (g) "DISTRIBUTION DATE" shall mean the earlier of (i) the Close of
          Business on the tenth day (or such later date as may be determined by
          action of the Company's Board of Directors) after the Shares
          Acquisition Date (or, if the tenth day after the Shares Acquisition
          Date occurs before the Record Date, the Close of Business on the
          Record Date), (ii) except as otherwise provided in clause (iii) below,
          the Close of Business on the tenth day (or such later date as may be
          determined by action of the Company's Board of Directors) after the
          date that a tender or exchange offer by any Person (other than the
          Company, any Subsidiary of the Company, any employee benefit plan of
          the Company or of any Subsidiary of the Company, or any Person or
          entity organized, appointed or established by the Company for or
          pursuant to the terms of any such plan) is commenced within the
          meaning of Rule 14d-2(a) of the General Rules and Regulations under
          the Exchange Act, if, assuming the successful consummation thereof,
          such Person would be the Beneficial Owner of 15% or more of the shares
          of Common Stock then outstanding, or (iii) with respect to (A) the
          tender offer (the "MENTOR TENDER OFFER") disclosed in a Tender Offer
          Statement on Schedule 14D-1, dated August 12, 1998, filed with the
          Securities and Exchange Commission by MGZ Corp., a Delaware
          corporation and wholly-owned subsidiary of Mentor Graphics
          Corporation, an Oregon corporation ("MENTOR"), and any amendment to
          such Mentor Tender Offer or (B) the commencement of a separate tender
          offer within the meaning of Rule 14d-2(a) of the General Rules and

 
          Regulations under the Exchange Act by Mentor or any Affiliate or
          Associate of Mentor, a date to be determined by the Company's Board of
          Directors.

     (c)  Paragraphs (i) through (k) of Section 1 of the Original Agreement are
hereby amended such that such paragraphs shall be labeled (h) through (j),
respectively.

     (d)  The following shall be inserted into Section 1 of the Agreement
immediately following Section 1(j):

          (k) "INTERESTED PERSON" with respect to a Transaction shall mean any
          Person who (i) is or will become an Acquiring Person if such
          Transaction were to be consummated or an Affiliate or Associate of
          such a Person, and (ii) is, or directly or indirectly proposed,
          nominated or financially supported, a director of the Company in
          office at the time of consideration of such Transaction who was
          elected at an annual or special meeting of stockholders.

     (e)  Section 1(l) of the Original Agreement is hereby deleted in its
entirety.

     (f)  Paragraphs (m) through (x) of Section 1 of the Original Agreement are
hereby amended such that such paragraphs shall be labeled (l) through (w),
respectively.

     (g)  The following shall be inserted into Section 1 of the Original
Agreement immediately following Section 1(w):

          (x) "TRANSACTION" shall mean any merger, consolidation or sale of
          assets described in Section 13(a) hereof or any acquisition of Common
          Shares which would result in a Person becoming an Acquiring Person.

2.   Amendment of "Adjustment of Purchase Price, Number of Shares or Number of
     -------------------------------------------------------------------------
Rights" Section. Section 11(a) of the Original Agreement is hereby deleted in
- ---------------                                                              
its entirety and the following is substituted therefore:

     (a)  (i)  In the event the Company shall at any time after the date of this
     Agreement (A) declare a dividend on the Common Shares payable in Common
     Shares, (B) subdivide the outstanding Common Shares, (C) combine the
     outstanding Common Shares (by reverse stock split or otherwise) into a
     smaller number of Common Shares, or (D) issue any shares of its capital
     stock in a reclassification of the Common Shares (including any such
     reclassification in connection with a consolidation or merger in which the
     Company is the continuing or surviving corporation), then, in each such
     event, except as otherwise provided in this Section 11(a) and Section 7(e)
     hereof: (1) each of the Rights outstanding at the time of the record date
     for such dividend or the effective date of such subdivision, combination or
     reclassification shall be proportionately adjusted to that number of Rights
     (calculated to the nearest one ten-thousandth (1/10,000) of a Right) equal
     to a fraction (the "EXCHANGE RATIO"), the numerator of which shall 

                                      -2-

 
     be the total number of Common Shares or shares of capital stock outstanding
     immediately following such subdivision, combination or reclassification and
     the denominator of which shall be the total number of Common Shares
     outstanding immediately prior to such time, and the number of Rights that
     shall thereafter be issued with respect to each Common Share or share of
     such other capital stock that shall become outstanding thereafter prior to
     the Distribution Date shall be equal to the total number of outstanding
     Rights immediately after such event (as adjusted pursuant to this clause
     (1)) divided by the total number of outstanding Common Shares or shares of
     such other capital stock immediately after such event (subject to further
     adjustment pursuant to the provisions of this Agreement); (2) the Purchase
     Price in effect at the time of the record date for such dividend or of the
     effective date of such subdivision, combination or reclassification shall
     be adjusted so that the Purchase Price thereafter shall equal the result
     obtained by dividing the Purchase Price in effect immediately prior to such
     time by the Exchange Ratio; provided, however, that in no event shall the
                                 --------  -------                            
     consideration to be paid upon the exercise of one Right be less than the
     aggregate par value of the shares of capital stock of the Company issuable
     upon exercise of such Right; and (3) the number of Common Shares or shares
     of such other capital stock issuable upon the exercise of each Right shall
     remain unchanged immediately after such event, but, in the event of a
     reclassification, the kind of shares issuable upon the exercise of each
     Right immediately after such reclassification shall be adjusted to be the
     kind of shares of such other capital stock issued in such reclassification,
     rather than Common Shares. If an event occurs which would require an
     adjustment under both this Section 11(a)(i) and Section 11(a)(ii) hereof,
     the adjustment provided for in this Section 11(a)(i) shall be in addition
     to, and shall be made prior to, any adjustment required pursuant to Section
     11(a)(ii) hereof.

          (ii)  Subject to Section 24 of this Agreement, in the event a
     Triggering Event shall have occurred, then promptly following such
     Triggering Event, proper provision shall be made so that each holder of a
     Right, except as provided in Section 7(e) hereof, shall thereafter have the
     right to receive for each Right, upon exercise thereof in accordance with
     the terms of this Agreement and payment of the then-current Total Exercise
     Price, in lieu of a number of one-thousandths of a Preferred Share, such
     number of Common Shares of the Company as shall equal the result obtained
     by multiplying the then-current Purchase Price by the then number of one-
     thousandths of a Preferred Share for which a Right was exercisable (or
     would have been exercisable if the Distribution Date had occurred)
     immediately prior to the first occurrence of a Triggering Event, and
     dividing that product by 50% of the current per share market price
     (determined pursuant to Section 11(d) hereof) for Common Shares on the date
     of occurrence of the Triggering Event (such number of shares being
     hereinafter referred to as the "ADJUSTMENT SHARES").

          (iii)  In lieu of issuing Common Shares in accordance with Section
     11(a)(ii) hereof, the Company may, if the Board of Directors determines
     that such action is necessary or appropriate and not contrary to the
     interest of holders of Rights (and, in the event that the number of Common
     Shares which are authorized by the Company's Certificate of Incorporation
     but not outstanding or reserved for issuance for purposes other than upon
     exercise of the Rights are not sufficient to permit the exercise in full of
     the Rights, or if any necessary regulatory approval for 

                                      -3-

 
     such issuance has not been obtained by the Company, the Company shall): (A)
     determine the excess of (1) the value of the Common Shares issuable upon
     the exercise of a Right (the "CURRENT VALUE") over (2) the Purchase Price
     (such excess, the "SPREAD") and (B) with respect to each Right, make
     adequate provision to substitute for such Common Shares, upon exercise of
     the Rights, (1) cash, (2) a reduction in the Purchase Price, (3) other
     equity securities of the Company (including, without limitation, shares or
     units of shares of any series of preferred stock which the Board of
     Directors of the Company has deemed to have the same value as Common Shares
     (such shares or units of shares of preferred stock are herein called
     "common stock equivalents")), except to the extent that the Company has not
     obtained any necessary stockholder or regulatory approval for such
     issuance, (4) debt securities of the Company, except to the extent that the
     Company has not obtained any necessary stockholder or regulatory approval
     for such issuance, (5) other assets, or (6) any combination of the
     foregoing, having an aggregate value equal to the Current Value, where such
     aggregate value has been determined by the Board of Directors of the
     Company based upon the advice of a nationally recognized investment banking
     firm selected by the Board of Directors of the Company; provided, however,
                                                             --------  -------
     if the Company shall not have made adequate provision to deliver value
     pursuant to clause (B) above within thirty (30) days following the later of
     (x) the first occurrence of a Triggering Event and (y) the date on which
     the Company's right of redemption pursuant to Section 23(a) expires (the
     later of (x) and (y) being referred to herein as the "SECTION 11(A)(II)
     TRIGGER DATE"), then the Company shall be obligated to deliver, upon the
     surrender for exercise of a Right and without requiring payment of the
     Purchase Price, Common Shares (to the extent available), except to the
     extent that the Company has not obtained any necessary stockholder or
     regulatory approval for such issuance, and then, if necessary, cash, which
     shares and/or cash have an aggregate value equal to the Spread. If the
     Board of Directors of the Company shall determine in good faith that it is
     likely that sufficient additional Common Shares could be authorized for
     issuance upon exercise in full of the Rights or that any necessary
     regulatory approval for such issuance will be obtained, the thirty (30) day
     period set forth above may be extended to the extent necessary, but not
     more than ninety (90) days after the Section 11(a)(ii) Trigger Date, in
     order that the Company may seek stockholder approval for the authorization
     of such additional shares or take action to obtain such regulatory approval
     (such period, as it may be extended, the "SUBSTITUTION PERIOD"). To the
     extent that the Company determines that some action need be taken pursuant
     to the first and/or second sentences of this Section 11(a)(iii), the
     Company (x) shall provide, subject to Section 7(e) hereof, that such action
     shall apply uniformly to all outstanding Rights and (y) may suspend the
     exercisability of the Rights until the expiration of the Substitution
     Period in order to seek any authorization of additional shares, to take any
     action to obtain any required regulatory approval and/or to decide the
     appropriate form of distribution to be made pursuant to such first sentence
     and to determine the value thereof. In the event of any such suspension,
     the Company shall issue a public announcement stating that the
     exercisability of the Rights has been temporarily suspended, as well as a
     public announcement at such time as the suspension is no longer in effect.
     For purposes of this Section 11(a)(iii), the value of the Common Shares
     shall be the current per share market price (as determined pursuant to
     Section 11(d) hereof) of the Common Shares on the Section 11(a)(ii) Trigger
     Date and the value of any "common stock equivalent" shall be deemed to have
     the same value as the Common Shares on such date.

                                      -4-

 
3.   Amendment of "Consolidation, Merger or Sale or Transfer of Assets or
     --------------------------------------------------------------------
Earning Power" Section. Section 13(d) of the Original Agreement is hereby
- ----------------------                                                   
deleted in its entirety and paragraphs (e) and (f) of Section 13 shall be
relabeled paragraphs (d) and (e), respectively.

4.   Amendment of "Redemption" Section.  Section 23 of the Original Agreement is
     ---------------------------------                                          
hereby deleted in its entirety and the following is substituted therefore:

     Section 23.  Redemption.
                  ---------- 

          (a) The Company may, at its option and with the approval of the Board
     of Directors, at any time prior to the Close of Business on the earlier of
     (i) the tenth day following the Shares Acquisition Date or such later date
     as may be determined by action of a majority of the Company's Board of
     Directors and publicly announced by the Company and (ii) the Final
     Expiration Date, redeem all but not less than all the then outstanding
     Rights at a redemption price of $0.01 per Right, appropriately adjusted to
     reflect any stock split, stock dividend or similar transaction occurring
     after the date hereof (such redemption price being herein referred to as
     the "REDEMPTION PRICE") and the Company may, at its option, pay the
     Redemption Price either in Common Shares (based on the current per share
     market price thereof (as determined pursuant to Section 11(d) hereof) at
     the time of redemption) or cash.  Such redemption of the Rights by the
     Company may be made effective at such time, on such basis and with such
     conditions as the Board of Directors in its sole discretion may establish.

          (b) Notwithstanding the provision of Section 23(a), in the event that
     a majority of the Board of Directors of the Company is elected by
     stockholder action at an annual or special meeting of stockholders, then
     until the 180th day following the effectiveness of such election (including
     any postponement or adjournment thereof), the Rights shall not be redeemed
     if such redemption is reasonably likely to have the purpose or effect of
     facilitating a Transaction with an Interested Person.

          (c) Immediately upon the action of the Board of Directors of the
     Company ordering the redemption of the Rights, evidence of which shall have
     been filed with the Rights Agent, and without any further action and
     without any notice, the right to exercise the Rights will terminate and the
     only right thereafter of the holders of Rights shall be to receive the
     Redemption Price. The Company shall promptly give public notice of any such
     redemption; provided, however, that the failure to give or any defect in,
                 --------  -------                                            
     any such notice shall not affect the validity of such redemption.  Within
     ten (10) days after the action of the Board of Directors ordering the
     redemption of the Rights, the Company shall give notice of such redemption
     to the Rights Agent and the holders of the then outstanding Rights by
     mailing such notice to all such holders at their last addresses as they
     appear upon the registry books of the Rights Agent or, prior to the
     Distribution Date, on the registry books of the transfer agent for the
     Common Shares.  Any notice which is mailed in the manner herein provided
     shall be deemed given, whether or not the holder receives the notice.  Each
     such notice of redemption will state the method by which the payment of the
     Redemption Price will be made.  Neither the Company nor any of its
     Affiliates or Associates may redeem, acquire or purchase for value any
     Rights at any time in any manner 

                                      -5-

 
     other than that specifically set forth in this Section 23 or in Section 24
     hereof, and other than in connection with the purchase of Common Shares
     prior to the Distribution Date.

5.   Amendment of "Exchange" Section.  Section 24 of the Original Agreement is
     -------------------------------                                          
hereby deleted in its entirety and the following is substituted therefore:

     Section 24.  Exchange.
                  -------- 

          (a) Subject to applicable laws, rules and regulations, and subject to
     subsections (b) and (d) below, the Company may, at its option, by action of
     the Board of Directors, at any time after the occurrence of a Triggering
     Event, exchange all or part of the then outstanding and exercisable Rights
     (which shall not include Rights that have become void pursuant to the
     provisions of Section 7(e) hereof) for Common Shares at an exchange ratio
     of one Common Share per Right, appropriately adjusted to reflect any stock
     split, stock dividend or similar transaction occurring after the date
     hereof (such exchange ratio being hereinafter referred to as the "RATIO OF
     EXCHANGE").  Notwithstanding the foregoing, the Board of Directors shall
     not be empowered to effect such exchange at any time after any Person
     (other than the Company, any Subsidiary of the Company, any employee
     benefit plan of the Company or any such Subsidiary, or any entity holding
     Common Shares for or pursuant to the terms of any such plan), together with
     all Affiliates and Associates of such Person, becomes the Beneficial Owner
     of 50% or more of the Common Shares then outstanding.

          (b) Notwithstanding the provision of Section 24(a), in the event that
     a majority of the Board of Directors of the Company is elected by
     stockholder action at an annual or  special meeting of stockholders, then
     until the 180th day following the effectiveness of such election (including
     any postponement or adjournment thereof), the Rights shall not be exchanged
     pursuant to Section 24(a) if such exchange is reasonably likely to have the
     purpose or effect of facilitating a Transaction with an Interested Person.

          (c) Immediately upon the action of the Board of Directors ordering the
     exchange of any Rights pursuant to subsection (a) of this Section 24 and
     without any further action and without any notice, the right to exercise
     such Rights shall terminate and the only right thereafter of a holder of
     such Rights shall be to receive that number of Common Shares equal to the
     number of such Rights held by such holder multiplied by the Ratio of
     Exchange.  The Company shall give public notice of any such exchange;
     provided, however, that the failure to give, or any defect in, such notice
     --------  -------                                                         
     shall not affect the validity of such exchange.  The Company shall mail a
     notice of any such exchange to all of the holders of such Rights at their
     last addresses as they appear upon the registry books of the Rights Agent.
     Any notice which is mailed in the manner herein provided shall be deemed
     given, whether or not the holder receives the notice.  Each such notice of
     exchange will state the method by which the exchange of the Common Shares
     for Rights will be effected and, in the event of any partial exchange, the
     number of Rights which will be exchanged.  Any partial exchange shall be
     effected pro rata based on the number of Rights (other than Rights which
     have become void pursuant to the provisions of Section 7(f) hereof) held by
     each holder of Rights.


                                      -6-

 
          (d) In the event that there shall not be sufficient Common Shares
     issued but not outstanding or authorized but unissued to permit any
     exchange of Rights as contemplated in accordance with Section 24(a), the
     Company shall either take such action as may be necessary to authorize
     additional Common Shares for issuance upon exchange of the Rights or
     alternatively, at the option of a majority of the Board of Directors, with
     respect to each Right (i) pay cash in an amount equal to the Current Value
     (as hereinafter defined), in lieu of issuing Common Shares in exchange
     therefor, or (ii) issue debt or equity securities or a combination thereof,
     having a value equal to the Current Value, in lieu of issuing Common Shares
     in exchange for each such Right, where the value of such securities shall
     be determined by a nationally recognized investment banking firm selected
     by majority vote of the Board of Directors, or (iii) deliver any
     combination of cash, property, Common Shares and/or other securities having
     a value equal to the Current Value in exchange for each Right.  For
     purposes of this Section 24(d) only, the Current Value shall mean the
     product of the current per share market price of Common Shares (determined
     pursuant to Section 11(e) on the date of the occurrence of the event
     described above in subparagraph (a)) multiplied by the number of Common
     Shares for which the Right otherwise would be exchangeable if there were
     sufficient shares available.  To the extent that the Company determines
     that some action need be taken pursuant to clauses (i), (ii) or (iii) of
     this Section 24(d), the Board of Directors may temporarily suspend the
     exercisability of the Rights for a period of up to sixty (60) days
     following the date on which the event described in Section 24(a) shall have
     occurred, in order to seek any authorization of additional Common Shares
     and/or to decide the appropriate form of distribution to be made pursuant
     to the above provision and to determine the value thereof.  In the event of
     any such suspension, the Company shall issue a public announcement stating
     that the exercisability of the Rights has been temporarily suspended.

          (e) The Company shall not be required to issue fractions of Common
     Shares or to distribute certificates which evidence fractional Common
     Shares.  In lieu of such fractional Common Shares, there shall be paid to
     the registered holders of the Rights Certificates with regard to which such
     fractional Common Shares would otherwise be issuable, an amount in cash
     equal to the same fraction of the current per share market value of a whole
     Common Share (as determined pursuant to the second sentence of Section
     11(e) hereof).

          (f) The Company may, at its option, by majority vote of the Board of
     Directors, at any time before any Person has become an Acquiring Person,
     exchange all or part of the then outstanding Rights for rights of
     substantially equivalent value, as determined reasonably and with good
     faith by the Board of Directors, based upon the advice of one or more
     nationally recognized investment banking firms.

          (g)  Immediately upon the action of the Board of Directors ordering
     the exchange of any Rights pursuant to subsection (f) of this Section 24
     and without any further action and without any notice, the right to
     exercise such Rights shall terminate and the only right thereafter of a
     holder of such Rights shall be to receive that number of rights in exchange
     therefor as has been determined by the Board of Directors in accordance
     with subsection (f) above.  The Company shall give public notice of any
     such exchange; provided, however, that the failure to 
                    --------  -------                                         

                                      -7-

 
     give, or any defect in, such notice shall not affect the validity of such
     exchange. The Company shall mail a notice of any such exchange to all of
     the holders of such Rights at their last addresses as they appear upon the
     registry books of the transfer agent for the Common Shares of the Company.
     Any notice which is mailed in the manner herein provided shall be deemed
     given, whether or not the holder receives the notice. Each such notice of
     exchange will state the method by which the exchange of the Rights will be
     effected.

6.   Amendment to "Supplements and Amendments" Section.  Section 27 of the
     -------------------------------------------------                    
Original Agreement is hereby deleted in its entirety and the following is
substituted therefore:

     Section 27.  Supplements and Amendments.
                  -------------------------- 

         (a) Prior to the Distribution Date, the Company may supplement or amend
     this Agreement in any respect without the approval of any holders of Rights
     and the Rights Agent shall, if the Company so directs, execute such
     supplement or amendment.  From and after the Distribution Date, the Company
     and the Rights Agent may from time to time supplement or amend this
     Agreement without the approval of any holders of Rights in order to (i)
     cure any ambiguity, (ii) correct or supplement any provision contained
     herein which may be defective or inconsistent with any other provisions
     herein, (iii) shorten or lengthen any time period hereunder, or (iv) change
     or supplement the provisions hereunder in any manner that the Company may
     deem necessary or desirable and that shall not adversely affect the
     interests of the holders of Rights (other than an Acquiring Person or an
     Affiliate or Associate of an Acquiring Person); provided, this Agreement
                                                     --------                
     may not be supplemented or amended to lengthen, pursuant to clause (iii) of
     this sentence, (A) a time period relating to when the Rights may be
     redeemed at such time as the Rights are not then redeemable or (B) any
     other time period unless such lengthening is for the purpose of protecting,
     enhancing or clarifying the rights of, and/or the benefits to, the holders
     of Rights (other than an Acquiring Person or an Affiliate or Associate of
     an Acquiring Person). Upon the delivery of a certificate from an
     appropriate officer of the Company that states that the proposed supplement
     or amendment is in compliance with the terms of this Section 27, the Rights
     Agent shall execute such supplement or amendment.  Prior to the
     Distribution Date, the interests of the holders of Rights shall be deemed
     coincident with the interests of the holders of Common Shares.

         (b) Notwithstanding the provisions of Section 27(a), in the event that
     a majority of the Board of Directors of the Company is elected by
     stockholder action at an annual or special meeting of stockholders, then
     until the 180th day following the effectiveness of such election (including
     any postponement or adjournment thereof), this Agreement shall not be
     supplemented or amended in any manner reasonably likely to have the purpose
     or effect of facilitating a Transaction with an Interested Person.

7.   Amendment of "Determinations and Actions by the Board of Directors, etc."
     -------------------------------------------------------------------------
Section.  Section 29 of the Original Agreement is hereby deleted in its entirety
- -------                                                                         
and the following is substituted therefore:


                                      -8-

 
       Section 29.  Determinations and Actions by the Board of Directors, etc.
                    ---------------------------------------------------------- 
     For all purposes of this Agreement, any calculation of the number of Common
     Shares outstanding at any particular time, including for purposes of
     determining the particular percentage of such outstanding Common Shares of
     which any Person is the Beneficial Owner, shall be made in accordance with
     the last sentence of Rule 13d-3(d)(1)(i) of the General Rules and
     Regulations under the Exchange Act. The Board of Directors of the Company
     shall have the exclusive power and authority to administer this Agreement
     and to exercise all rights and powers specifically granted to the Board, or
     the Company, or as may be necessary or advisable in the administration of
     this Agreement, including, without limitation, the right and power to (i)
     interpret the provisions of this Agreement and (ii) make all determinations
     deemed necessary or advisable for the administration of this Agreement
     (including a determination to redeem or not redeem the Rights or to amend
     the Agreement).  All such actions, calculations, interpretations and
     determinations (including, for purposes of clause (y) below, all omissions
     with respect to the foregoing) which are done or made by the Board in good
     faith, shall (x) be final, conclusive and binding on the Company, the
     Rights Agent, the holders of the Rights Certificates and all other parties
     and (y) not subject the Board to any liability to the holders of the
     Rights.

8.   Amendment of "Exhibit C".  Exhibit C of the Original Agreement is hereby
     ------------------------                                                
deleted in its entirety and Exhibit C as attached hereto is substituted
therefore.

9.   Ratification of Original Agreement.  Except as amended hereby, the Original
     ----------------------------------                                         
Agreement remains unchanged and is ratified and confirmed in all respects.



                                      -9-

 
     IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 1 to
Rights Agreement to be duly executed as of the day and year first above written.

"COMPANY"                           QUICKTURN DESIGN SYSTEMS, INC.


                                    By: /s/ Keith R. Lobo
                                        -------------------------------------
                                        Keith R. Lobo
                                        President and Chief Executive Officer


"RIGHTS AGENT"                      BANKBOSTON, N.A.


                                    By: /s/ Geoffrey D. Anderson
                                        ---------------------------------------
 
                                    Name: Geoffrey D. Anderson
                                         -------------------------------------- 
                                    Title:  Director
                                         -------------------------------------- 





                     [AMENDMENT NO. 1 TO RIGHTS AGREEMENT]

 
                                   EXHIBIT C
                                   ---------

                        QUICKTURN DESIGN SYSTEMS, INC.

                            STOCKHOLDER RIGHTS PLAN

                               Summary of Rights
                               -----------------


Distribution and        The Board of Directors has declared a dividend of one 
- ----------------        Right for each outstanding share of Common Stock of   
Transfer of Rights;     Quickturn Design Systems, Inc. (the "COMPANY"). Prior 
- -------------------     to the Distribution Date referred to below, the Rights
Rights Certificate:     will be evidenced by and trade with the certificates  
- ------------------      for the Common Stock. After the Distribution Date, the
                        Company will mail Rights certificates to the Company's
                        stock holders and the Rights will become transferable  
                        apart from the Common Stock.                            
                         
Distribution Date:      Rights will separate from the Common Stock and become
- -----------------       exercisable on the earlier of (i) the tenth day (or such
                        later date as may be determined by a majority of the
                        Company's Board of Directors) after a person or group
                        acquires beneficial ownership of 15% or more of the
                        Company's Common Stock, (ii) the tenth day (or such
                        later date as may be determined by the Company's Board
                        of Directors) after a person or group announces a tender
                        or exchange offer, the consummation of which would
                        result in ownership by a person or group of 15% or more
                        of the Company's Common Stock, or (iii) with respect to
                        (A) the tender offer (the "TENDER OFFER") disclosed in a
                        Tender Offer Statement on Schedule 14D-1, dated August
                        12, 1998, filed with the Securities and Exchange
                        Commission by MGZ Corp., a Delaware corporation and
                        wholly-owned subsidiary of Mentor Graphics Corporation,
                        an Oregon corporation ("MENTOR"), and any amendment to
                        such Tender Offer or (B) the commencement of a separate
                        tender offer within the meaning of Rule 14d-2(a) of the
                        General Rules and Regulations under the Exchange Act by
                        Mentor or any Affiliate or Associate of Mentor, a date
                        to be determined by the Company's Board of Directors.

Preferred Stock         After the Distribution Date, each Right will entitle the
- ---------------         holder to purchase, for fifty dollars ($50) a fraction
Purchasable Upon        of a share of the Company's Preferred Stock with      
- ----------------        economic terms similar to that of one share of the    
Exercise of Rights:     Company's Common Stock.                                
- ------------------                                                           
                        

 
Flip-In:                If an acquiror obtains 15% or more of the Company's 
- -------                 Common Stock, thereby becoming an "ACQUIRING PERSON",
                        then each Right (other than Rights owned by an Acquiring
                        ----
                        Person or its affiliates) will entitle the holder
                        thereof to purchase, for the exercise price, a number of
                        shares of the Company's Common Stock having a then
                        current market value of twice the exercise price.

Flip-Over:              If, after the Shares Acquisition Date (defined below), 
- ---------               (a) the Company merges into another entity, (b) an
                        acquiring entity merges into the Company or (c) the
                        Company sells more than 50% of the Company's assets or
                        earning power, then each Right (other than Rights owned
                                       ----
                        by an Acquiring Person or its affiliates) will entitle
                        the holder thereof to purchase, for the exercise price,
                        a number of shares of Common Stock of the person
                        engaging in the transaction having a then current market
                        value of twice the exercise price.

Exchange Provision:     At any time after an event triggering the flip-in or 
- ------------------      flip-over rights and prior to the acquisition by the
                        Acquiring Person of 50% or more of the outstanding
                        Common Stock, the Board of Directors of the Company may
                        exchange the Rights (other than Rights owned by the
                        Acquiring Person or its affiliates), in whole or in
                        part, at an exchange ratio of one Common Share per Right
                        (subject to adjustment).

Redemption of           Rights will be redeemable at the Company's option for 
- -------------           $0.01 per Right at any time on or prior to the 
the Rights:             Distribution Date, (i.e., the tenth day (or such later  
- ----------              date as may be determined by the Company's Board of
                        Directors) after public announcement that a person has  
                        acquired beneficial ownership of 15% or more of the     
                        Company's Common Stock (the "SHARES ACQUISITION DATE")).
                        
Expiration of           The Rights expire on the earliest of (a) January 10,  
- -------------           2006, (b) exchange or redemption of the Rights as     
the Rights:             described above, or (c) consummation of a merger or   
- ----------              consolidation resulting in expiration of the Rights as
                        described above.                                       
                        
Amendment of            The terms of the Rights and the Rights Agreement may be 
- ------------            amended in any respect without the consent of the Rights
Terms of Rights:        holders on or prior to the Distribution Date;          
- ---------------         thereafter, the terms of the Rights and the Rights
                        Agreement may be amended without the consent of the    
                        Rights holders in order to cure any ambiguities or to  
                        make changes which do not adversely affect the interests
                        of Rights holders (other than the Acquiring Person).   
                        
                                      -2-
                        

 
Delay of Exchange,      The Company's ability to exchange or redeem the Rights 
- ------------------      and the Company's ability to amend the Rights Agreement
Redemption              will be prohibited for a period of 180 days following  
- ----------              the election of a majority of the Company's directors if
or Amendment            it would have the purpose or effect of facilitating a  
- ------------            Transaction with an Interested Person.
                        
Voting Rights:          Rights will not have any voting rights.
- -------------                                          

Anti-Dilution           Rights will have the benefit of certain customary anti-
- -------------           dilution provisions. 
Provisions:  
- ----------                                                                  
              
Taxes:                  The Rights distribution should not be taxable for      
- -----                   federal income tax purposes. However, following an 
                        event which renders the Rights exercisable or upon
                        redemption of the Rights, stockholders may recognize
                        taxable income.                        

The foregoing is a summary of certain principal terms of the Stockholder Rights
Plan only and is qualified in its entirety by reference to the detailed terms of
the Rights Agreement dated as of January 10, 1996, as amended, between the
Company and the Rights Agent.





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