The final task is to conduct radiated measurements on a TxM without the shield and compare the results to those of a TxM with MicroShield integrated RF shielding technology applied. For accurate measurements, leaking RF power from connectors and other onboard circuitry on the test board must be prevented; therefore, the test board designed for these measurements contains separate shield cans as shown in Figure 5.

All radiated measurements were performed at Delta Technologies in Copenhagen, Denmark. The device under test is placed on top of a non-absorbing and non-reflective material (Figure 6). In this example another one of RFMD's TxM products, the RF3282, was used as the test vehicle.

Figure 7 shows the radiated power from the RF3282 TxM. The red graph represents the TxM with no shield and the blue graph represents the TxM using MicroShield. Note that the blue graph has been shifted slightly to the right to better illustrate the difference between the two devices under test. As shown in the graph, MicroShield integrated RF shielding reduces the radiated power significantly. Only one caveat was observed at 10.5 GHz. It appears that either another mode exists (cavity mode) or perhaps the results could be related to ground current flowing on the top surface of the shield. Nevertheless, the average attenuation in radiated power amounts to 15 dB or better.

We have discussed the benefits of MicroShield as it relates to EMI and RFI emissions, improving the ability to meet specifications. Additionally, MicroShield integrated RF shielding minimizes exposure to external EMI/RFI as well, resulting in lower susceptibility to performance shifts seen during handset design. A component's sensitivity to board placement is a critical factor as handset designers and manufacturers increasingly rely upon handset platforms to satisfy their time and cost requirements. Traditionally, when these platforms are applied to individual handset designs, performance can suffer, with EMI and RFI emissions often prime contributors to performance inconsistencies. With MicroShield enabled RF components, handset manufacturers are able to place highly complex RF modules as they would any component that is insensitive to EMI/RFI, providing a true “plug-and-play” solution that is robust to board design and layout changes. By eliminating sensitivity to board placement, MicroShield eliminates the risk of circuit retuning, thereby accelerating time-to-market and reducing the cost of RF implementation.

The authors would like to thank in particular Mick Zhou in the modeling team at RFMD and also Scott Morris and Milind Shah at RFMD Corporate R&D packaging.

1. David M. Pozar, Microwave engineering, ISBN 0-201-50418-9.

Ulrik Riis Madsen received his B.Sc with honours in Electrical Engineering from Aarhus University, Denmark, in June 1996. Until October 1999, he was employed with Dancall Telecom in Denmark. He joined RFMD in 1999 and has designed several key power amplifier modules and also conceptualized the PowerStar concept. Madsen is currently a staff engineer in the corporate research and development group with RF Micro Devices.

Carsten Hinrichsen received his M.Sc.EE. from AAU, Denmark in 1993. During his career in the RF industry he has worked in DanPhone (PMR), Dancall/Bosch telecom and Texas Instruments. For the past three years he has worked as a GSM PA designer at RF Micro Devices. Hinrichsen holds several patents in various aspects of RF design.

Click here for the enhanced PDF version of this article

Previous 1 2 3