Electronic Design

Class 1 Power Amplifiers Handle Any Bluetooth Application

The PA2423 family of Class 1 power amplifiers (PAs) from SiGe Semiconductor provides something for every designer of Bluetooth-enabled applications. Its members are available in three different packages—an eight-lead MSOP, a six-lead LPCC, and a gold-bumped flip chip—accommodating almost any design variation.

The Bluetooth standard specifies three power levels: Class 3 with with 0 dBm (1 mW), Class 2 with 4 dBm (2.5 mW), and Class 1 with 20 dBm (100 mW). Over 40% of all Bluetooth designs will use the higher-power Class 1 configuration.

Most Bluetooth RF chips put out 1 mW, or 2.5 mW at most, severely restricting the signal's reach. That's enough for many applications that range up to 10 m. But longer distances, applications that require wireless operation through walls, and applications with potential multipath obstructions all need higher power to ensure a reliable connection. For wireless LANs and some personal-area network (PAN) uses, the 100-mW power level is essential to achieving a robust system. This extra power is obtained with an external PA.

The PA2423 family fills this need in Bluetooth products. These Class A bipolar silicon-germanium (SiGe) linear amplifiers have a 45% efficiency. They're designed for 100% duty cycle operation and operate with a supply of 3 to 3.6 V. Their current drain is 125 mA with the full power output. They put out a total of 22.5 dBm. The extra 2.5 dBm is added to compensate for the losses associated with filters, Z matching, and transmission lines between the PA and the antenna. Power stability is 1 dB over the −40°C to 85°C range. Full-power output is readily achieved with a 0- to 4-dBm input and a maximum input power of 8 dBm.

The chips have two power control inputs. The digital input line turns the device off or on with less than 3 dB of overshoot as required by the Bluetooth specifications. In the off mode, the chips draw only 0.5 µA. The other power control input is full analog with zero power out with zero control input and maximum power output with a full Vcc input as specified by the Bluetooth standard.

The PA2423MB MSOP costs $1.44 in 10,000-unit quantities. The PA2423G flip chip and PA2423L LPCC cost $1.50 and $1.44, respectively, in 10,000-unit quantities.

SiGe Semiconductor, 2680 Queensview Dr., Ottawa, Ontario, Canada K2B 8J9; (613) 820-9244, (877) 602-SIGE; www.sige.com.

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