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Power detectors shrink to 1mm?

Posted: 15 Jul 2005 ?? ?Print Version ?Bookmark and Share

Keywords:lmv225? lmv228? lmv226? power detector? national semiconductor?

For handset designers on the look out for power detectors, there are some major areas of concern: temperature stability, dynamic range, waveform response, power consumption and size. With its new line of LMV225/226/228 log amp RF power detectors and the LMV232 mean-square RF detector, National Semiconductor Corp. has skillfully looked over the list and hit or exceeded all of its design target specs.

It's imperative that RF detectors provide a response that is temperature independent, and the design team at National Semiconductor worked to achieve power measurement errors that were as tight as possible. For instance, at 900MHz, RFIN = 0dBm, the LMV225 features 0.64/-1.07dB variation due to temperature, and at 1,800MHz, RFIN = 15dBm, the LMV226 features 0.07/-0.10dB variation due to temperature.

In terms of dynamic range, the LMV225 features an RF power detection range of -30dBm to 0dBm, and the other members of the family offer variants in dynamic range and configurations for application-specific reasons.

"Output voltage response to different input power signals is another critical area of concern for RF power detectors, which is why we have launched both traditional log linear/log amp detectors as well as a means squared architecture, or accurate power measurement with the LMV232," explains David Bernardo from National Semiconductor's Amplifiers product group. The LMV232 provides a DC output voltage that is independent of the wave shape of the input signal, which can be very important in systems with complex wave shapes, such as wideband CDMA (W-CDMA).

These RF power detectors gain a competitive edge in size, since they are available in micro SMD packaging that measures 1-by-1-by-0.6mm. The LMV225 and LMV228 are also available in a 2.2-by-2.5-by-0.8mm Leadless lead frame package (LLP). The LMV232 mean-square RF detector measures 1.5-by-1.5-by-0.6mm.

Manufactured using a BiCMOS process, the devices were carefully optimized for power consumption, another major concern for handset designers who are struggling to pack more functionality into phones while maintaining talk time. All of the devices operate with a single supply range from 2.7Vdc to 5Vdc. The LMV225/226/228 devices typically draw 4.8mA power in active mode and 0.44?A in shutdown mode. The LMV232 mean-square RF detector typically draws 9.8mA power in active mode and 0.09?A in shutdown mode.

These are National Semiconductor's first entries in the RF power detector market, and they have leveraged some intellectual property form PA loop controllers as well as their experience in wireless handset markets to optimize the new devices. "We developed these products because we felt that we had a technology that is compelling to our customers," observes Bernardo, "And, it will allow us to move into additional applications, such as communication infrastructure and test and measurement."

According to the LMV225/226/228 design team, the primary challenge was to achieve sufficient accuracy at high frequencies with as low power consumption as possible. The designers looked carefully at architectures, optimized circuitry, and also spent a significant amount of time on layout optimization.

For the LMV232, the team focused on reducing internal device offsets to be able to achieve a wide dynamic range and a high temperature accuracy. To do this on a small die area, they used a proprietary offset cancellation technique.

The teams' work has clearly paid off, and these RF detectors deserve a closer look from handset designers.

The LMV225 and LMV228 are priced at 41 cents each in 1,000-piece quantities, while the LMV226 is priced at 53 cents in 1,000-piece quantities. Samples and production quantities are already available.

- Janine Love


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