PA manages to boost standard, EDR Bluetooth signals

Designers of Bluetooth devices know that Bluetooth with enhanced data rate (EDR) gives a performance boost and extends battery life as compared to standard Bluetooth, and these are two very important considerations in portable devices that are being asked now to use Bluetooth for multiple functions, sometimes simultaneously.

The team at SiGe Semiconductor, always on the lookout for how they can help designers get the job done faster and better, has extended their RangeCharger IC product line with the SE2425U power amplifier (PA) for Bluetooth.

There are two especially interesting things about this new PA. First, it is optimized for both standard Bluetooth and Bluetooth with EDR. How can that be? Well, they put a CMOS mode pin on the PA, which interfaces directly with the baseband or transceiver and allows the biasing to be changed. So, with a standard packet, the mode can be set low, and, with an EDR packet, you pull the pin high so it will give optimal performance in EDR mode. With this PA, you can get optimal performance in either mode, as compared to picking a PA with performance that falls in the middle of both.

The second notable characteristic of this device is its integration. Typically, you would expect a Bluetooth PA to require eight to 12 external components to complete the circuit. With the SE2425U, all you need are two external capacitors because the input match, interstage match and most of the output match are integrated. The obvious benefits here are the smaller footprint and simpler design. Since there is no need to design matching circuitry, this makes it easier to add Bluetooth functionality to existing designs.

When the design team at SiGe was working on this new product, one of their goals was to integrate as much as possible, yet still make it small enough to fit in embedded devices. The result is a PA that is only 0.5mm in height and measures 3-by-3mm.

"Achieving this level of integration was the greatest design challenge with the SE2425U," reports Andrew Parolin, director of wireless data products, SiGe Semiconductor, "There is a reason the other PAs are not as well integrated, and that's because it is difficult to do." Truth be told, the team admits that you can integrate, but the real challenge is keeping a high level of performance. So, how'd they do it? "We saw the same trends in our cellphone and WLAN PAs, so we were able to leverage our work there to the Bluetooth market."

Another challenge was the difficulty in offering a low quiescent current and high output power. "The EDR modulation has similar requirements as WLAN where you need a very linear PA, and we were able to bring that design experience over to Bluetooth. It's relatively easy to get good linearity by throwing current at the problem. The challenge was to keep the quiescent current low."

So, what about performance? SiGe reports that the SE2425U delivers 25dBm output power in standard mode and 19.5dBm in EDR mode. Another notable spec for this product is its quiescent current, which runs at 29mA.

If you're looking to design a product with Bluetooth, especially an embedded design, it might serve you well to give this product a closer look. The good news is, it is already sampling. In fact, some devices are already in play on customers' boards. Also available, a full evaluation kit, Gerber files, schematics and BOM.

The SE2425U is currently available, and is priced at 95 cents in 10,000 quantities.

- Janine Love
eeProductCenter