With the ever-increasing use of electronic equipment comes a greater likelihood of interference from all the other equipment out there. In the same vein, we’re seeing more circuits, with lower power levels, that are easily disturbed; so, there’s a need to protect equipment from EMI (electromagnetic interference). In automotive or medical applications, for example, there can be no false alarms due to external interference. The level of uncertainty has pushed EMI compliance testing to the component level.

To meet international legislation such as the EU Directive on EMC or the FCC, EMI filtering is an essential element of equipment design. Introducing screening measures to case or cables, for example, may suffice in many instances, but you might need to introduce low-pass filtering for additional protection as well. Here, we will begin to explore EMI filtering and the terminology used in designing effective protection.

In mission-critical applications, additional screening and testing is required to ensure that only the most robust parts make it to the finished product. Preventative measures, like high quality standards, lessen the possibility of failure in the field and minimize the likelihood of astronomical downstream costs.

Supply noise creates challenges in RF systems where it can mix with RF signals, impacting signal-to-noise ratios and potentially causing spurious output. Thus, high-frequency monolithic microwave integrated circuit (MMIC) amplifiers with broadband gain need to be protected from RF noise on the supply lines. Avoiding these issues with supply line noise requires RF designers to use a bypass capacitor that provides an efficient path to ground for RF energy on the supply line before it enters a gain stage (Figure 1).

Imaging systems account for a significant portion of the medical devices and electronics industry. There is an expanding range of imaging modalities, and one of the most common is magnetic resonance imaging (MRI). MRI equipment uses a strong magnetic field and computer-generated radio waves to create cross sectional images of the body; these images enable health care professionals to investigate and diagnose without the need for an invasive procedure.

One of the questions we get asked regularly is:

‘why not just integrate a filter in the board stack?’

Our answer to this comes in two parts: First there are manufacturing tolerances to consider, and second there is size.

With the promised delivery date of 5G wireless communication fast approaching, the world is waiting to see if this next-generation network will hit its ambitious goals of 10 Gbps peak data rates, less than 1 ms latency, 10 times greater energy efficiency, and more. In past decades, each generation of mobile systems – from 1G analog systems to 2G digital standards to 3G mobile broadband capabilities to 4G LTE and LTE-Advanced networks – has overcome a unique set of challenges. Leaps in technology are necessary to enable these advancements in performance.

From Ultrasound to Radars, in a phased array system some of the most important design considerations are the number of elements and the element spacing since both drive cost and performance. In traditional arrays an inter element spacing of less than half the wavelength (<λ/2) is required to mitigate grating lobes.

Microwave and mmWave frequencies are found in RF applications and in optical communications. As we see increasing interest in mmWave for RF communications and move from 28Gbps to 56Gbps NRZ and 112Gbps PAM4 in the optical world, the system as a whole needs to maintain a high interconnect bandwidth.

Planar Filters

Manufactured using a thin-film process, Microstrip (planar) filters can offer a high quality factor (Q) and a reduced packaging envelope when compared to discrete lumped element designs, and are more practical at higher frequencies. The thin-film design can hold tighter design tolerances due to the distributed transmission lines forming resonant structures. Planar filters are a robust solution, attractive for applications ranging from established platforms, such as military warfare, to emerging technologies, like 5G. Below are some general-purpose resources for additional background, applications, and benefits of Microstrip filters: