Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 74

Oscillators in some ways represent the most non‐linear of electrical circuits with frequencies created at the output with no input (other than noise). Oscillators have a wide variety of characteristics that are important to characterize, including output frequency, output power, harmonics, phase noise, frequency pushing (change in frequency with change in DC power), frequency pulling (change in frequency due to change in load impedance), and output match.

Voltage‐controlled oscillators (VCOs) have the additional ability to control the frequency of the output due to a voltage change at the input. The voltage‐to‐frequency control factor is a key attribute of a VCO. A related microwave component is a yttrium‐iron‐garnet (YIG) oscillator, which uses a spherical YIG resonator as the frequency control element of the YIG‐tuned‐oscillator (YTO). The YIG resonator has the characteristic that the resonant frequency changes with magnetic field. YTOs have wide tuning bandwidth (up to 10:1) and low phase noise. Tuning is performed by changing the current in an electromagnet but can be very low bandwidth due to the large inductance of the magnet. YTOs often have a second, lower inductance coil (called the FM coil), which provides small change to frequency but with high bandwidth.

As the focus of this book is stimulus/response measurements, the measurement of oscillators will not be covered.