An oscillator creates a new radio frequency signal from a DC source.
Any element with gain can be made to oscillate through the use of positive feedback. The active device is biased on, and creates noise. The output noise spectrum is sampled, filtered to the desired frequency of oscillation, and fed back in phase to the input of the device, using either shunt or series feedback. The result is an AC output signal at the frequency for which the feedback is peaked.
Alternately, a reflection oscillator can be created from any acitve device that has gain and is not unconditionally stable. The active element, called the negative R (resistance) cell, is biased on. It is then terminated with a load (called the resonator or tank circuit) that reflect the output noise spectrum of the negative R cell in such a way that the standing wave produced creates a new AC signal. If the resonator can be tuned by an external voltage, for example by using a varactor diode which changes capacitance as a function of applied voltage, then the oscillator is called a Voltage Controlled Oscillator, or VCO.
Agilent Technologies Products for Oscillator Applications
- Discrete Devices:
- Comparison of transistors as RF/uw oscillators
- Transistors as oscillators in millimeter wave Receivers, Direct Tansmitters, or Upconverting Transmitters
- Hybrid Circuits:
- VTO-8000 series, VTO-9000 series
- System Soultions:
- The oscillator function is included in the HPMX-5001 IC.