Negative R is gain that an active device provides in an oscillator circuit to overcome losses and sustain oscillation. Major component of the circuit loss is the resistance of the quartz crystal. Crystal Manufacturers specify this resistance in their crystal data sheets. Dominant Failure Mode for an Oscillator Circuit with Low Negative R or High Crystal Resistance is the oscillator failing to start when power is applied to the circuit. Negative R is an important concept in designing Oscillators. Definition of Terminology and Test Methodology is crucial for successful communication between customers and vendors. Terms should be clearly defined as misstated Jargon can cause catastrophic production and field failures.
To know how much negative R do we need? Refer to Cypress white paper- Crystal Oscillator Design and Negative Resistance by Anthony M. Scalpi available at:
http://www.cypress.com/?docID=9180
