RF Oscillator Features and Performance Considerations For 5G Applications

Given the stringent timing requirements of 5G network and wireless applications, RF oscillator performance is of increasingly critical importance. Noise and phase noise are among the most significant of these requirements, as these parameters have the greatest impact on communication signal quality and receiver capability. Though noise and phase noise have always been RF oscillator key considerations, phase noise requirements are becoming even more stringent with the extremely high levels of modulation for 5G modulation, such as 64-256QAM, cyclic prefix Orthogonal Frequency Division Multiplexing (CP-OFDM, and discrete Fourier transform OFDM (DFT-s-OFDM). These higher order modulation schemes are more susceptible to signal quality degradation from noise and phase noise, and hence the increase in oscillator requirements when deploying these technologies to achieve higher throughput.

Noise and phase noise are intrinsic aspects of oscillators, and no current oscillator technologies are without these unwanted phenomena. There are a variety of different noise generating components within an RF oscillator, the main cause of phase noise is the conversion of these noise sources to the frequency domain (as phase modulation of the signal) where they emerge as jitter/phase noise (random variations of the frequency) in the oscillator signal. The phase noise introduced in the oscillator signal may then be passed along and exacerbated by the active frequency translation electronics and other active components in the signal chain resulting in potentially significant performance impact.

Other use-case level concerns include timing stability in time-synchronized networks. For instance, new 5G applications such as augmented reality, responsive edge networks, and real-time 5G applications require high levels of time synchronization to function with an acceptable user experience. IEEE 1588 and eCPRI are technologies designed to enable time synchronization over packet networks. However, packet network technologies come with the catch of introducing time-delay variation in the packets traveling between links, packet delay variation (PDV), from the interconnect and active components, such as switches. These time variations can be minimized sign extremely stable, low noise, and low phase noise oscillators.

When connecting a central unit (CU) to a remote radio head (RRU), PDV can be mitigated somewhat by high performance oscillators within the IEEE 1588 servo loop. This is due to the servo loop acting as a low pass filter to the PDV and a high pass filter to oscillator-induced timing noise. Hence, a higher performance oscillator will allow for a lower servo-loop bandwidth adjustable to the input PDV and result in an output clock that is an accurate recreation of the time scale at the origin. This corrected clock signal is able to accurately discipline the oscillator within the continuously updating feedback loop.

Given that 5G systems may also be in more integrated packages installed in a wide variety of environments, the environmental ruggedness of oscillators is also among the top considerations. For instance, some oscillator technologies exhibit poor frequency stability over temperature and during shock/vibration events. Therefore, it is important to have oscillator technology that is compensated and ruggedly packaged to reduce the influence of environmental factors on oscillator performance in 5G networks that are ever more susceptible to performance degradation due to weak oscillator performance.

Learn more about Pasternack’s RF Oscillators for 5G Applications: https://www.pasternack.com/pages/RF-Microwave-and-Millimeter-Wave-Products/rf-oscillators-for-5g.html

Also, you can learn more about 5G Oscillator requirements in this article by Pasternack experts published by Microwave Journal: https://www.microwavejournal.com/articles/34412-the-growing-importance-of-oscillators-with-5g