Electronic Design

Bluetooth EDR Apps Get Giant Range Boost From Tiny Power Amplifier

Bluetooth is a great short-range wireless technology for cell phones, laptops, PDAs, headsets, peripherals, and other devices. But it quickly runs out of steam when the range goes beyond 10 m. It's particularly troublesome with enhanced data rate (EDR) Bluetooth applications that use the full-bore 3-Mbit/s rate. SiGe Semiconductor's SE2425U power amplifier (PA) may have the solution (Fig. 1).

The Bluetooth specifications include three classes of power amplification. Class 3 is standard 1 dBm. The SE2425U supports classes 1 and 2 with 20-dBm and 4-dBm power output, respectively. With class 1 power, a Bluetooth EDR device can reach up to 100 m, depending, of course, on the environment.

The three-stage amplifier is made with silicon-germanium (SiGe) biCMOS (Fig. 2). It operates from a 3.3-V supply and delivers an output power of +25 dBm using the standard Bluetooth mode with

Gaussian frequency shift keying (GFSK) and a power of +19.5 dBm when operating with 9/4-DQPSK (differential quadrature phase-shift keying) or 8-DPSK ( differential phase-shift keying) as required for EDR. Operating current is 110 mA at the maximum EDR rate. The quiescent current is 29 mA.

The SE2425U also can reduce over-power consumption, boosting battery life. The EDR rate sends data faster, so the total transmit time for a packet is significantly reduced. This greatly lowers power consumption as well. And, the SE2425U can control the bias on the amplifier to optimize its operation to the Bluetooth mode.

In standard mode, the packet header and the payload both are transmitted using GFSK at 1 Mbit/s. In the EDR mode, the header is transmitted using GFSK so any nearby Bluetooth device, including non-EDR devices, can determine the mode from the header. The EDR packet payloads are then transmitted in 8-DPSK.

When transmitting in the standardrate GFSK mode (1 Mbit/s), the amplifier can operate fully saturated. This greatly improves efficiency (45%) and reduces power consumption. In the EDR mode, the bias is readjusted for more linear operation to accommodate the 8-DPSK modulation, with 22% efficiency. Bias is changed with the mode pin on the chip.

Finally, the SE2425U eliminates the need for most external components, especially those used for input and output impedance matching. The input and interstage matches are all on-chip. Most of the output matching components, including inductors, are on-chip. All you need is a couple of external capacitors to complete the match to the antenna.

The device comes in a 16-pin quad flat no-lead (QFN) package that measures 3 by 3 by 0.5 mm. With these dimensions, as well as its low power consumption, there's no longer any excuse to avoid including extra power in your Bluetooth application, extending its range and reliability. Available now, the SE2425U costs $0.95 in quantities of 10,000.

SiGe Semiconductor Inc.

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