Frequency reference standards are essential to achieving frequency accuracy and phase stability in electronic systems. Such sources require low phase noise and excellent frequency stability. But requirements for modern systems are also pressuring designers to reduce the size and cost of these reference standards, creating a set of conflicting requirements. Fortunately, a patented approach1-16 for voltage-controlled crystal oscillators (VCXOs)—even those with relative low quality-factor (Q) resonators—helps achieve excellent phase noise and frequency stability.