RF power supply tech is one of the most important parts of radio frequency (RF) design. There are many factors to consider when selecting a power supply. Here are a few things to keep in mind:
Low-noise regulators
There are many benefits of low-noise regulators in RF power supply tech. First, these regulators preserve signal integrity and allow for high-speed operation without any loss in RF power. Secondly, linear regulators preserve signal integrity by eliminating the effect of AM noise. A p1dB compression circuit is used to reduce the impact of AM noise. Most engineers have not tested their own RF power supply to measure it’s AM-PM conversion.
Moreover, low-noise regulators are indispensable for noise-sensitive RF applications. These regulators feature low-noise linear operation and are often used in conjunction with a multi-loop error amplifier. Low-noise regulators have excellent power supply ripple rejection and low output voltage noise. They also allow for low ground current consumption, making them a perfect fit for battery-operated portable applications.
Injection-locked magnetrons
RF power supply tech uses injection-locked magnetrons. This technology works by locking the output frequency of the magnetron to a drive signal, usually an LLRF. The drive signal is provided to the transmitter by an amplifier 115. The magnetron receives this signal and injects it through circulators. The magnetrons lock to the drive signal’s phase and frequency, thereby maintaining a constant output frequency.
Among its advantages, this method has an enhanced average relative efficiency and an extended range of power control. The power control bandwidth is approximately 10 dB, which is appropriate for various SRF accelerators and ADS-class projects. Additionally, a single-channel magnetron transmitter with an injection-locking signal is capable of dynamic wideband phase and mid-frequency power control. In a frequency-locked magneton, the phase-pushing process is controlled by controlling the current of the magnetron.
Class D amplifiers
When it comes to RF power supply tech, Class D amplifiers are an excellent choice. They provide power efficiency and low losses, and are easy to design for battery power. The use of off-the-shelf ICs makes them easy to incorporate into a battery-powered device. Recent advances have made it possible to design Class D amplifiers without any external filters, which reduces the size and cost of the design.
While reducing the size and power consumption of a Class D amplifier, it can also be used to boost signal levels. Low-resistance output transistors are especially important, as the simultaneous turn-on of MH and ML transistors can lead to large shoot-through currents, damaging the transistors. To avoid this condition, break-before-make control is a good choice. Nonoverlap time, also known as dead time, is also important to the overall sound quality of Class D amplifiers.
Low-noise transformers
High-frequency RF applications have high demands on low-noise transformers. As the frequency of the signals increases, parasitic properties of the transformer become more critical. These characteristics are often a part of the customer specification. Furthermore, resonant circuit topologies are driving new requirements for transformers. Below are some tips to help you make the best choice for your application. The following article explores some of the key factors to consider when purchasing low-noise transformers for RF power supply tech.
The noise from the RF power supply is usually conditioned before routing to the antenna or a u.FL or SMA coaxial line. The output of the RF power supply goes through a filter, which may be a BAW or SAW. These filters are not always able to accept high RF powers, so it is crucial to choose a low-noise transformer to ensure your RF power supply is free from unwanted noise.
Filtering
EMI (electromagnetic) emissions from switch-mode power supplies are notoriously large. The high-voltage nodes and fast switching of current results in a huge di/dt, or difference in voltage/current ratio, at an extremely wide frequency range. In fact, regulatory bodies have put limits on the maximum allowed levels of electromagnetic noise. While power supply manufacturers have spent considerable time developing and incorporating ways to reduce these emissions, some still remain. Fortunately, manufacturers have spent considerable time identifying sources of noise and then using filters to reduce the amount of residual emissions.
While traditional RF power amplifiers use discrete filters, newer components allow for aggressive form factors and the consolidation of multiple elements onto a single board. Before choosing a filter design, engineers should consult with the design team to ensure the proposed filtering system will be fabricated on a hybrid board. Additionally, transmission line design should take into account copper roughness and dielectric dispersion. By understanding these issues, the final RF power supply will function efficiently without noise, a necessary criterion in the design process.
