Current Progress

Time Line




            Negative resistance is a difficult parameter to measure in most crystal oscillator circuits.  As of now, there is no standard method to measure negative resistance and methods that do exist are heavily dependent on the oscillator circuit topology.  Hence, the goal of the project is to develop a standard method to measure negative resistance that will work for any oscillator topology.  The main focus of this method will be to measure the negative resistance supplied during oscillator startup.  If insufficient negative resistance exists at startup the oscillator will never reach steady state oscillation.               The motivation for developing a standard method to measure negative resistance is two fold.  First is customer satisfaction.  Cypress develops oscillator circuits to be paired with customer’s crystal resonators.  These oscillator circuits are required to provide adequate negative resistance to the crystal to reliably achieve startup.  Customers who purchase these Cypress oscillator circuits measure the negative resistance to be sure it will be enough to meet specifications for the crystal.  However, because there is no standard method of measurement for negative resistance the customer may employ a method that will not work with the Cypress oscillator topology the end result being an erroneous measurement.  Although Cypress simulations may show that the oscillator circuit will meet specifications for the crystal, the customer may conclude the opposite based on the erroneous measurement.  This discrepancy between simulation and customer measurements can loose customers and hurt business. 
            The second motivation is related to the first.  To satisfy the customer, Cypress may be forced to over-design for negative resistance.  Trades offs exist between negative resistance and other oscillator circuit performance parameters such as phase noise and jitter.  Over-designing for negative resistance will require sacrificing performance in these other areas, so optimizing the negative resistance is important.