Camarillo, Calif.-based Semtech Corp., a supplier of analog and mixed-signal semiconductors for computer, communication and industrial applications, announced that the employment of its president and CEO, Jason L. Carlson, has been terminated, effective immediately, by mutual agreement. Carlson also resigned as a member of Semtech's board of directors. Former CEO John D. Poe, now board chairman, will serve as acting CEO until a permanent replacement is found.    . . .    Grier C. Raclin has been named executive vice president, general counsel and corporate secretary of broadband service provider Charter Communications Inc. of St. Louis. Raclin most recently served as chief legal officer and corporate secretary for Savvis Communications Corp., an IT outsourcing services company based in St. Louis.    . . .    Telecom equipment manufacturer ECI Telecom Ltd. of Petah Tikva, Israel, and its Russian counterpart, MMG Ltd. of Moscow, have agreed to end their joint marketing activities in Russia, effective immediately. As part of the agreement, MMG's telecom sales and support teams will join ECI's Russian subsidiary to serve customers.