Ceramic CapacitorApplication Support
Approach in selection of capacitors for base station issues

In the design of base stations, which are becoming progressively smaller and are using even higher frequency bands, it is difficult to compromise due to the number of components that can be mounted on limited substrate space, and restrictions in the size and operating temperature of components.

To solve these issues, Murata Manufacturing Co., Ltd. presents a lineup of small capacitors with excellent high frequency characteristics. These capacitors can reduce the number of mounted components needed, and whose operation is guaranteed at high temperatures.

Base station PAs become hot due to heat generated by circuit boards and components. In particular, the amplification transistor generates a large amount of heat, and the DC cut and matching capacitors placed in the vicinity are exposed to high temperatures. In addition, the amplified power is received, and the capacitor itself generates more heat.

While the number of components has increased due to the recent trend of multiple-output (increase in Tx), the base station has become smaller, so there is less space for heat sink. In addition, as the frequency band used increases, the heating value of components increases and it becomes apparent that controlling the heating value of capacitors and the ambient temperature to a maximum of 125°C is a constraint on circuit design. In this situation, as well as the High-Q capacitors used for DC cutting and matching capacitors, decoupling capacitors for PA Vdrain power supply have also experienced cases exceeding 125°C.

Murata offers a lineup that includes conventional 150°C-guaranteed High-Q capacitors and 150°C -guaranteed general decoupling capacitors. This lineup reduces the temperature constraints for using capacitors around the PA and increases design flexibility. In addition, in order to meet conventional temperature requirements, Murata offers a lineup of 125°C guaranteed products, so that you can choose the product with the maximum temperature required according to the environment around the parts.

While the number of components mounted on base station PAs is increasing due to the shift to multiple-output (increase in Tx), the size of the equipment would be maintained or reduced, so it is becoming important to increase the density of circuit boards.
In addition, PA peripheral circuits, which were traditionally designed in discrete form, are increasingly being designed in modular form to increase size constraints and manufacturing efficiency as Tx increases. Therefore, it is necessary to reduce the matching capacitor.

Murata offers a lineup of High-Q capacitors that include the conventional 0402 size as well as the 0201 size and less. By using a special structure and materials, higher Q value is achieved compared to standard specifications (GRM series), even for capacitors with a low capacitance value. This small size and high Q value matching capacitor contributes to the higher density of high-frequency PA circuits.

Due to improved communication performance, IC performance at base stations is also increasing, and the total capacitors capacitance required continue to increase. On the other hand, because the size of equipment must be maintained or reduced in size, it is becoming important to increase the density of circuit boards.

As electronics become more and more sophisticated, they require tighter power line voltage controls, such as CPUs, and larger capacitance to maintain power line stability. This trend is also evident in base stations, where IC performance is increasing as the amount of information processing increases. As a result, large-capacitance capacitors are being used while being connected in parallel. Meanwhile, as the number of on-board parts increases due to multiple-output (increased Tx) specifications, the area of the decoupling capacitor must be reduced. In addition, while the advantage of an electrolytic capacitor is the large capacitance that can be obtained per unit, there is a risk of reliability in an environment of long-term continuous use at high temperatures, as with a base station.

Murata offers a lineup of over 100uF capacitors that can achieve a high capacitance while occupying a small area. Because the base station is used in a severe environment, the components on board are subject to severe operating conditions. However, Murata offers a lineup of 125°C guaranteed products, which can be used in such a severe temperature environment. In addition to capacitors over 100uF, Murata has also expanded a lineup of capacitors with a rated voltage of 100 V, which can be widely used in the 48 V power supply line, to be compact and capable of handling high temperatures. The combination of space saving, high capacitance, and high temperature support enhances design flexibility.