Timing is everything for many systems, especially for modern electronic systems with high-speed data converters and high-resolution sampling. A clock source is “the keeper of time” in these systems and system timing performance is very much dependent upon the performance of its clock source. For some system designers, a clock source automatically means a crystal oscillator, typically a single-frequency source. But some system designers, especially those faced with synchronizing systems at multiple clock frequencies, have learned to appreciate the flexibility of using voltage-controlled oscillators (VCOs) as clock sources.
Voltage Controlled Oscillators (VCOs) are normally designed for operation in an ideal 50 ohm environment. However, the actual load that these oscillators must drive are considerably different. It is a standard industry practice to measure frequency variation when the VCO output realizes a load with 12dB return loss (for all possible phase angles). This is usually performed as a manual measurement and is very time consuming. It may take a skilled technician several minutes to several hours. Fortunately, with the development of a novel electronic line stretcher from Mini-Circuits, these once tedious tests can now be executed quickly and a automatically.