Meaning
Electronic circuit that generates a high-frequency sinusoidal signal for use in frequency conversion is the reference source in transceiver architectures. This local oscillator provides the stable frequency that is mixed with an incoming radio signal to produce an intermediate frequency. The signal must have high spectral purity and low phase noise to prevent signal degradation during the mixing process.
It is used in both receivers and transmitters to shift signals up or down the frequency spectrum. Modern communication systems require these circuits to tune across wide frequency bands quickly while maintaining excellent frequency stability.
Frequency Synthesizer
Generation of this frequency often involves a voltage-controlled oscillator driven by a phase-locked loop. This configuration allows the output frequency to be adjusted in precise steps by changing the division ratio in the feedback loop. The stability of the generated signal is derived directly from a high-quality reference oscillator, such as a temperature-compensated crystal oscillator.
Mixer Interaction
Port-to-port isolation within the frequency converter prevents the generated signal from leaking into the antenna port. If the signal leaks to the antenna, it can be radiated and cause interference with other receivers in the vicinity. Additionally, a strong local signal leaking into the input port can self-mix, creating a DC offset that desensitizes the receiver.
Circuit Sourcing
Procuring the active oscillator components requires balancing phase noise specifications against power consumption and cost. For demanding applications like satellite communications or radar, designers select oven-controlled oscillators to achieve the lowest possible temperature drift. In mass-produced consumer electronics, integrated silicon synthesizers are preferred for their small size and low cost, even if they have higher phase noise.
