<PAGE>


                                  EXHIBIT 10.20
                                -----------------

                                 NOGATECH, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT

         THIS SERIES A PREFERRED STOCK PURCHASE AGREEMENT is entered into as of
December 27, 1995, by and among NOGATECH, INC., a California corporation
(hereinafter the "Corporation"), and Andrew Schonzeit (hereinafter referred to
as the "Investor").

                                    RECITALS

         A.       The Corporation desires to raise money by the sale of Series A
Preferred Stock to the Investor.

         B.       The Investor desires to purchase shares of Series A Preferred
Stock from the Corporation, and the Corporation desires to sell shares of Series
A Preferred Stock to the Investor, on the terms and conditions hereinafter set
forth.

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the mutual agreements, covenants,
representations and warranties contained in this Agreement, the parties agree as
follows:

         1.       AUTHORIZATION AND SALE OF PREFERRED STOCK.

                  a.       AUTHORIZATION. The Corporation will authorize on, or
before, the Closing the sale and issuance of up to four million four hundred
forty-four thousand four hundred forty-four (4,444,444) shares of its Series A
Convertible Preferred Stock (hereinafter the "Series A Preferred Stock") to the
Investor, having the rights, privileges and preferences as set forth in the
Amended and Restated Articles of Incorporation (hereinafter the "Articles") in
the form attached to this Agreement as Exhibit A.

                  b.       SALE OF SERIES A PREFERRED STOCK. Subject to the
terms and conditions hereof, the Corporation will issue and sell to the
Investor, one hundred forty-eight thousand one hundred forty-eight (148,148)
shares of Series A Preferred Stock (the "Shares") at a per share purchase price
of 3,375/10,000 U.S. Dollars ($0.3375), for an aggregate purchase price of Fifty
Thousand U.S. Dollars (U.S. $50,000).

         2.       ISSUANCE AND PAYMENT.

                  a.       CLOSING. Subject to the terms and conditions hereof,
the closing of the purchase and sale of the Shares (here-

<PAGE>

inafter the "Closing") shall be held (via facsimile transmittal and wire
transfers or cashier's check) at the Corporation's counsel's offices located at
1999 Harrison Street, Suite 1300, Oakland, California, on, or about, December
27, 1995, at 5:00 p.m., local time, or at such other time and place upon which
the Corporation and the Investor shall agree (the date of the Closing is
hereinafter referred to as the "Closing Date"). If Investor chooses to wire the
purchase price, the wire transfer shall be sent to Pezzola & Reinke's Attorney
Trust Account at: SUMMIT BANK, 2969 Broadway, Oakland, CA 94611; for deposit
into ACCOUNT NO. 01-20019741 (Summit Bank's telephone number is (510) 839-8800
and its ABA Number is 121138958). The wire instructions shall include a message
identifying the name of the Investor as the originator of the wire. If Investor
chooses to send a cashier's check, it shall be made payable to "Pezzola & Reinke
Trust Account for the benefit of Nogatech, Inc." and shall identify Investor as
the originator.

                  b.       CLOSING. At the Closing or as soon as practical
thereafter, the Corporation will deliver to the Investor a certificate,
registered in its name, representing the Shares to be purchased by the Investor,
against payment of the purchase price therefor, by cashier's check payable to
the Corporation, or by wire transfer through the Corporation's counsel, Pezzola
& Reinke, or as otherwise instructed by the Corporation.

         3.       CORPORATION'S WARRANTIES. The Corporation hereby represents
and warrants effective as of the Closing as follows:

                  a.       CORPORATE ORGANIZATION AND STANDING. The Corporation
is a corporation duly organized, existing and in good standing under the laws of
the State of California. The Corporation has the requisite corporate power to
carry on its business as presently conducted, and as proposed or contemplated to
be conducted in the future, and to enter into and carry out the provisions of
this Agreement and the transactions contemplated hereby. The Corporation is not
presently qualified to do business as a foreign corporation in any jurisdiction
where the failure to be so qualified would materially and adversely affect the
Corporation's business.

                  b.       SUBSIDIARIES. The Corporation has no subsidiaries or
affiliated companies and does not otherwise own or control, directly or
indirectly, any equity interest in any corporation, association or business
entity, except for its Israeli subsidiary, Nogatech, Ltd.

                  c.       CORPORATE CAPITALIZATION.

                           i.       Immediately prior to, or simultaneously
with, the Closing, the Corporation's authorized capital stock shall include only
two authorized classes of capital stock consisting of (i) sixteen million
(16,000,000) shares of Preferred Stock, fifteen million (15,000,000) shares of
which shall be designated as Series


                                      -2-

<PAGE>

A Convertible Preferred Stock, and (ii) forty million (40,000,000) shares of a
sole class of Common Stock. The Corporation intends to issue in late November,
1995 through early December, 1995 an aggregate of four million four hundred
forty-four thousand four hundred forty-four (4,444,444) shares of series A
Preferred Stock, including the issuance of the shares hereunder (the "Intended
Series A Shares"). Immediately prior to, or simultaneous with, the Closing
(without taking into consideration the Closing), the Corporation will have a
total of five hundred seventy-three thousand two hundred fifty (573,250) shares
of Common Stock outstanding; and up to one million four hundred eighty thousand
three hundred twenty-five (1,480,325) shares of Common Stock subject to issuance
pursuant to outstanding options (the "Options") granted to employees under stock
plans or to certain investors under option agreements. All issued and
outstanding shares of capital stock will have been duly authorized and validly
issued and will be fully paid and nonassessable. The Corporation has reserved
four million four hundred forty-four thousand four hundred forty-four
(4,444,444) shares of Series A Preferred Stock for issuance of the Intended
Series A Shares and four million four hundred forty-four thousand four hundred
forty-four (4,444,444) shares of Common Stock for issuance upon conversion. The
Corporation has also reserved (a) four million four hundred forty-four thousand
four hundred forty-four (4,444,444) shares of its Common Stock for issuance upon
conversion of the Series A Convertible Preferred Stock issued and outstanding
prior to the issuance hereunder; (b) one million four hundred eighty thousand
three hundred twenty-five (1,480,325) shares of its Common Stock for issuance
upon exercise of the Options.

                           ii.      Except as contemplated or set forth in this
Agreement, there are no outstanding preemptive or other rights, options,
warrants, conversion rights or agreements for the purchase or acquisition from
the Corporation of any shares of its capital stock.

                           iii.     As of the date hereof, the Corporation does
not have any declared and unpaid dividends (whether payable in cash, securities
or other consideration).

                  d.       AUTHORIZATION. All corporate action on the part of
the Corporation, its directors and shareholders necessary for the authorization,
execution, delivery and performance of this Agreement by the Corporation, the
authorization, sale, issuance and delivery of the Series A Preferred Stock (and
the Common Stock issuable upon conversion of the Series A Preferred Stock) and
the performance of all of the Corporation's obligations hereunder has been taken
or will be taken prior to the Closing. This Agreement, when executed and
delivered by the Corporation, shall constitute a valid and binding obligation of
the Corporation, enforceable in accordance with its terms, except as may be
limited by principles of public policy, and subject to laws of general
application relating to bankruptcy, insolvency and the relief of debtors and
rules of law governing specific performance, injunctive relief or


                                      -3-

<PAGE>

other equitable remedies. The Shares, when issued in compliance with the
provisions of this Agreement, will be validly issued, will be fully paid and
nonassessable, and will have the rights, preferences and privileges described in
the Articles; the Common Stock issuable upon conversion of the Shares has been
duly and validly reserved and, when issued in compliance with the provisions of
this Agreement and the Articles, will be validly issued, fully paid and
nonassessable; and the Shares and such Common Stock will be free of any liens or
encumbrances, assuming the Investor takes the Shares with no notice thereof,
other than any liens or encumbrances created by or imposed upon the Shares
hereunder; provided, however, that the Shares (and the Common Stock issuable
upon conversion thereof) may be subject to restrictions on transfer under state
and/or federal securities laws.

                  e.       FINANCIAL STATEMENTS. The Corporation has made
available to the Investor the consolidated audited Balance Sheet and Statement
of Operations of the Corporation, together with its subsidiaries, for the period
ended August 31, 1995 (collectively the "Financial Statements"). The Financial
Statements are complete and correct in all material respects. To the
Corporation's knowledge, the Financial Statements accurately set out and
describe the Corporation's financial condition and operating results and that of
its subsidiary as of the dates, and during the periods, indicated therein. To
the Corporation's knowledge, since August 31, 1995 there has not been any
material change in the assets, liabilities, financial condition or operations of
the Corporation or its subsidiary, from that reflected in the Financial
Statements, except changes in the ordinary course of business which have not
been, either in any case or in the aggregate, materially adverse.

                  f.       MATERIAL LIABILITIES. Neither the Corporation nor its
subsidiary has any material liabilities or obligations, absolute or contingent
(individually or in the aggregate), except (i) the liabilities and obligations
set forth in the Financial Statements; (ii) liabilities and obligations which
have been incurred subsequent to August 31, 1995 in the ordinary course of
business which have not been, either in any case or in the aggregate, materially
adverse; and (iii) liabilities and obligations under a lease for its principal
offices and leases for equipment and liabilities and obligations under sales,
procurement and other contracts and arrangements entered into in the normal
course of business.

                  g.       LITIGATION. There are no actions, proceedings or, to
the Corporation's best knowledge, investigations pending, or any threat thereof,
against or affecting the Corporation which, either individually or in the
aggregate, might result in any material adverse change in the business,
prospects, condition, affairs or operations of the Corporation or in any of its
properties or assets, or in any material impairment of the right or ability of
the Corporation to carry on its business as proposed to be


                                      -4-

<PAGE>

conducted, and none which questions the validity of this Agreement or any action
taken or to be taken in connection herewith.

                  h.       GOVERNMENTAL CONSENTS. To the Corporation's
knowledge, no consent, approval, order, authorization or registration,
qualifications, designation, license, declarations or filings with any Federal
or state governmental authority is required on the part of the Corporation in
connection with the consummation of the transactions contemplated herein, except
for applicable security law filings and the IITSSA filing set forth in Section
4(h) below.

                  i.       REGISTRATION RIGHTS. The Corporation has granted
registration rights to the current holders of the shares of Series A Convertible
Preferred Stock, as successors in interest to the prior holders of such shares,
pursuant to the terms and conditions set forth in a Stock Purchase Agreement
dated as of January 1, 1993 (the "1993 Agreement"), among the Corporation, DSP
Group, Inc. and Scitex Corporation, Ltd. Except as provided hereunder and in the
1993 Agreement, the Corporation is not a party to any "registration rights
agreement" or any similar agreement pursuant to which any person would have the
right to cause, under any circumstances, the registration of securities under
the Securities Act of 1933, as amended (the "Securities Act").

                  j.       DISCLOSURE. No representation or warranty by the
Corporation in this Agreement or in any statement or certificate furnished or to
be furnished to the Investor pursuant hereto or in connection with the
transactions contemplated hereby contains or will contain any untrue statement
of a material fact or omits or will omit to state a material fact necessary to
make the statements made therein, in the light of the circumstances under which
they were made, not misleading.

                  k.       SURVIVAL OF REPRESENTATIONS. All representations made
by the Corporation in or under this Agreement shall be true and accurate as of
the Closing.

         4.       INVESTOR REPRESENTATIONS AND WARRANTIES. The Investor
represents and warrants to the Corporation that:

                  a.       INVESTMENT. The Investor is acquiring the Shares and
any shares of Common Stock issuable pursuant to conversion of the Shares
(hereinafter collectively the "Securities") for investment for their own
account, and not with a present intention to resell in connection with, any
distribution thereof, and they have no present intention of selling or
distributing any such Securities. It understands that the Securities have not
been registered under the Securities Act by reason of a specific exemption from
the registration provisions of the Securities Act which depends upon, among
other things, the bona fide nature of the investment as expressed herein.


                                      -5-

<PAGE>

                  b.       RULE 144. The Investor acknowledges that because the
Securities have not been registered under the Securities Act, the Securities
must be held indefinitely unless subsequently registered under the Securities
Act or an exemption from such registration is available. The Investor is aware
of the provisions of Rule 144 promulgated under the Securities Act which permits
limited resale of shares purchased in a private placement under certain
circumstances.

                  c.       NO PUBLIC MARKET. The Investor understands that no
public market now exists for any securities issued by the Corporation and that
it is uncertain whether a public market will ever exist for any such securities.

                  d.       ACCESS TO DATA. The Investor has had an opportunity
to discuss the Corporation's business, management and financial affairs with its
management and to obtain any additional information given to it necessary or
appropriate for deciding whether or not to purchase the Securities. The Investor
acknowledges that no representations or warranties have been made by the
Corporation or any agent thereof except as set forth in this Agreement.

                  e.       INVESTMENT EXPERIENCE. The Investor is an "accredited
investor" as that term is defined in Regulation D promulgated by the Securities
and Exchange Commission.

                  f.       PREVIOUS INVESTMENTS. The Investor is an investor in
securities of companies in the development stage and acknowledges that it is
able to fend for itself, can bear the economic risk of its investment and has
such knowledge and experience in financial or business matters that it is
capable of evaluating the merits and risks of the investment contemplated
herein.

                  g.       RISKS. The Investor understands that an investment in
the Corporation involves a high degree of risk and is suitable only for an
investor who can afford a loss of their entire investment and who have no need
for liquidity from their investment.

                  h.       IITSSA COMPLIANCE. The Investor shall provide to the
Corporation all such information as is necessary to complete the forms required
to be filed by the Corporation with the U.S. Department of Commerce, Bureau of
Economic Analysis, under the International Investment and Trade in Services
Survey Act, as amended, and regulations issued thereunder.

                  i.       GOVERNMENTAL CONSENTS. To the Investor's knowledge,
no consent, approval, order, authorization or registration, qualifications,
designation, license, declarations or filings with any Israeli governmental
authority is required on the part of the Investor in connection with the
consummation of the transactions contemplated herein.


                                      -6-

<PAGE>

         5.       RESTRICTIVE LEGENDS. Each certificate or other written
documentation representing any of the Securities which the Investor is
purchasing or may purchase hereunder and any other securities issued upon any
stock split, stock dividend, recapitalization, merger, consolidation or similar
event (unless no longer required in the opinion of the counsel for the
Corporation) shall be stamped or otherwise imprinted with a legend substantially
in the following form:

         "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
         REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR QUALIFIED
         UNDER ANY STATE SECURITIES LAW, AND MAY NOT BE SOLD, TRANSFERRED,
         ASSIGNED OR HYPOTHECATED UNLESS THERE IS AN EFFECTIVE REGISTRATION
         STATEMENT UNDER SUCH ACT COVERING SUCH SECURITIES, OR THE HOLDER
         RECEIVES AN OPINION OF COUNSEL FOR THE HOLDER OF THE SECURITIES
         SATISFACTORY TO THE CORPORATION, STATING THAT SUCH SALE, TRANSFER,
         ASSIGNMENT OR HYPOTHECATION IS EXEMPT FROM THE REGISTRATION AND
         PROSPECTUS DELIVERY REQUIREMENTS OF SUCH ACT AND THE QUALIFICATION
         REQUIREMENTS UNDER STATE LAW."

         The Corporation shall be entitled to enter stop transfer notices on its
stock books with respect to the Securities.

         6.       AFFIRMATIVE COVENANTS OF THE CORPORATION. So long as the
Investor owns of record and beneficially at least fifty percent (50%) of the
Series A Preferred Stock shares purchased by it hereunder, until the Corporation
effects a registered underwritten public offering of its common stock, the
Corporation shall deliver to such Investor internally prepared quarterly and
annual financial statements.

         7.       REGISTRATION RIGHTS. At any time after three (3) years from
the Closing Date, or eighteen (18) months after the Corporation's initial public
offering, whichever is earlier, Persons holding at least twenty percent (20%) of
the Common Stock issuable upon conversion of all the Series A Preferred Stock
may request registration by the Corporation of their shares, if the anticipated
aggregate gross cash proceeds would exceed Ten Million Dollars ($10,000,000). In
such event, the Corporation will use its best efforts to cause such shares to be
registered. The Corporation shall only be obligated to effect two (2)
registrations under these demand registration rights provisions. Persons holding
Series A Preferred Stock or Common Stock issuable upon conversion of the Series
A Preferred Stock, shall be entitled to S-3 registration rights no more often
than once per every eighteen (18) month period on form S-3, if available for use
by the Corporation, for an aggregate offering price of at least One Million
Dollars ($1,000,000) per offering. Persons holding Series A Preferred Stock or
Common Stock issuable upon conversion of the Series A Preferred Stock shall be
entitled to unlimited "piggyback" registrations on a registration of the
Corporation's equity, subject to a prorata cutback with all those holding
"piggyback" registration rights in the underwriters' discretion and reasonable


                                      -7-

<PAGE>

lock-ups as requested by underwriters. The registration expenses (exclusive of
underwriting discounts and commissions) shall be borne by the Corporation for
all permitted registrations.

         8.       NEGATIVE COVENANTS. The Corporation shall not, without the
vote or written consent of the holders of a majority of the shares of Series A
Stock, voting as a separate class:

                           i.       create any new class or series of shares
having preference over the Series A Stock;

                           ii.      merge, consolidate, or reorganize, where
such merger, consolidation, or reorganization results in the change of a
majority of the members of the Board of Directors;

                           iii.     sell all or substantially all of its assets
or sell more than 50% of the Corporation's Common Stock in one transaction or
series of related transactions.

                           iv.      enter into a transaction with a related
party on terms and conditions which are not done in the ordinary course of
business or which are not done on terms and conditions which represent a fair
value to the Corporation.

         9.       MISCELLANEOUS.

                  a.       SURVIVAL. The covenants and agreements made herein
shall survive the Closing of the transactions contemplated hereby and shall end
when fewer than fifty percent (50%) of the Shares are outstanding or upon the
consummation of an initial public offering of any of the Corporations' shares.

                  b.       SUCCESSORS AND ASSIGNS. Except as otherwise expressly
provided herein, the provisions hereof shall inure to the benefit of, and be
binding upon, the successors, assigns, heirs, executors and administrators of
the parties hereto.

                  c.       ENTIRE AGREEMENT. This Agreement and the exhibits
attached hereto and the other documents delivered pursuant hereto constitute the
full and entire understanding and agreement between and among the parties with
regard to the subjects hereof and thereof.

                  d.       NOTICE. Any notice, payment, report or other
communication required or permitted to be given by one party to any other party
by this Agreement shall be in writing and either (i) served personally on the
other party or parties; (ii) sent by express, registered or certified first
class mail, postage prepaid, addressed to the other party or parties at its or
their address or addresses as indicated next to their signatures below, or to
such other address as any addressee shall have theretofore furnished to


                                      -8-

<PAGE>

the other parties by like notice; (iii) delivered by commercial courier to the
other party or parties; or (iv) sent by facsimile. Such notice shall be deemed
received on the second day after transmittal if sent by one day courier together
with a transmission of such notice by facsimile if the recipient has the
capability to receive a facsimile at its address and if sent by other methods
shall be deemed received upon receipt.

                  e.       FINDER'S AND BROKER'S FEES. The Corporation and
Investor each represents and warrants that it has retained no finder or broker
in connection with the transactions contemplated by this Agreement. Each party
hereby agrees to indemnify and to hold the other harmless from any liability for
any finder's or broker's fee to any broker or other person or firm (and the
costs and expenses of defending against such liability or asserted liability)
for which such indemnifying person, or any of its employees or representatives,
are responsible.

                  f.       TITLES AND SUBTITLES. The titles of the Sections and
subsections of this Agreement are for the convenience of reference only and are
not to be considered in construing this Agreement.

                  g.       COUNTERPARTS. This Agreement may be executed in any
number of counterparts, each of which shall be an original, but all of which
together shall constitute one instrument.

                  h.       APPLICABLE LAW. This Agreement shall be governed by
and construed in accordance with the laws of the State of California applicable
to contracts between California residents entered into and to be performed
entirely within the State of California.

                  i.       USE OF PROCEEDS. The Corporation may use the proceeds
of this financing for (i) working capital purposes; or (ii) capital investment.

                  j.       ARBITRATION. Any dispute between the parties arising
out of this Agreement shall be submitted to final and binding arbitration in the
City of Cupertino, County of Santa Clara, State of California, under the
Commercial Arbitration Rules of the American Arbitration Association then in
effect, upon written notification and demand of either party therefor. In the
event either party demands such arbitration, the American Arbitration
Association shall be requested to submit a list of prospective arbitrators
consisting of persons experienced in matters involving securities offerings. The
provisions of California Code of Civil Procedure Section 1283.05 and the laws of
the State of California are incorporated herein and shall be applicable to the
arbitration. In making the award, the arbitrator shall award recovery of costs
and expenses of the arbitration and reasonable attorneys' fees to the prevailing
party. Any award may be entered as a judgment in any court of competent
jurisdiction.


                                      -9-

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                  (REMAINDER OF PAGE INTENTIONALLY LEFT BLANK.)


                                      -10-

<PAGE>

         Should judicial proceedings be commenced to enforce or carry out this
provision or any arbitration award, the prevailing party in such proceedings
shall be entitled to reasonable attorneys' fees and costs in addition to other
relief. Either party shall have the right, prior to receiving an arbitration
award, to obtain preliminary relief from a court of competent jurisdiction to
avoid injury or prejudice to that party.

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the day and year hereinabove first written.

CORPORATION:

NOGATECH, INC.
a California corporation
20300 Stevens Creek Boulevard, 4th Fl.
Cupertino, California 95014

By: /s/ Arie Heiman
   ------------------------------
           (Signature)

---------------------------------
      (Print Name and Title)

<TABLE>
<CAPTION>

INVESTOR:                                                 NUMBER OF SHARES:
--------                                                  ----------------
<S>                                                       <C>
                                                               148,148
</TABLE>


/s/ Andrew Schonzeit
------------------------------------
         (Signature)

Andrew U. Schonzeit
------------------------------------
         (Print Name)

255 W. 88th St.  #2c
------------------------------------
         (Print Address)
NY, NY 10024
------------------------------------


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