APPLICATION INFORMATION 2.45 GHz power amplifier with the BFG480W Philips Semiconductors Application information 2.45 GHz power amplifier with the BFG480W ABSTRACT • Description of the product The BFG480W, one of the Philips double polysilicon wideband transistors of the BFG400 series. These transistors are characterised by a transition frequency higher than 20 GHz at low supply voltages. • Application area Low voltage high frequency wireless applications. • Presented application A power amplifier for a 2.45 GHz WLAN. • Main results At a frequency of 2.45 GHz, a supply voltage of 3.0 V, and a control voltage of 3.0 V, the amplifier delivers an output power of 19 dBm at an input power of 8 dBm, with a power added efficiency of 38 %. PHILIPS ELECTRONICS N.V. 1999 All rights are reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor imply any license under patent- or other industrial or intellectual property rights. 1999 Dec 03 2 Philips Semiconductors Application information 2.45 GHz power amplifier with the BFG480W INTRODUCTION With the Philips double polysilicon wideband transistor BFG480W, it is possible to design Power Amplifiers (PAs) for high frequency applications with a low current and a low supply voltage. The transistors have a transition frequency higher than 20 GHz at low supply voltages. This application note gives an example of a power amplifier with the BFG480W for a frequency of 2.45 GHz for a Wireless Local Area Network (WLAN). PERFORMANCE OVERVIEW The measurements on the amplifier in the Continuous Wave (CW) mode of operation have been done under the following conditions: • Vsupply = 3.0 V • Vcrtl = 3.0 V • Isupply = 64 mA • Pi = 8 dBm • f = 2.45 GHz • Zi =50 Ω; Zo = 50 Ω. Table 1 Measuring results of the PA (CW mode of operation) SYMBOL PARAMETER CONDITIONS VALUE UNIT Po output power 19 dBm GP power gain 11 dB ηPA power added efficiency note 1 38 % ηtot total efficiency note 2 41 % VSWRIN input voltage standing wave ratio 2 Notes 1. Po – Pi The power added efficiency is defined as η PA = ----------------------------------------× 100% . V supply × I supply 2. Po The total efficiency is defined as η tot = ----------------------------------------× 100% . V supply × I supply 1999 Dec 03 3 Philips Semiconductors Application information 2.45 GHz power amplifier with the BFG480W CIRCUIT DESCRIPTION The power amplifier operates at a single supply voltage of 3.0 V. It consists of the BFG480W wideband transistor, operating in class AB. Biasing for load power adjustment is performed by an external control voltage and a circuit with an NPN transistor BC817. The BFG480W has two emitter-leads which have to be carefully grounded to ensure stable operation and performance according to the specification. The PCB layout (see Fig.2) of the amplifier results in an emitter-to-ground inductance of 130 pH (typical value). CIRCUIT DIAGRAM handbook, full pagewidth Vsupply Vctrl R1 L1 R3 R2 C7 C6 TR2 µS4 C3 µS3 µS1 input 50 Ω µS2 C1 C4 TR1 C2 MGS763 Fig.1 Circuit diagram. 1999 Dec 03 C5 4 output 50 Ω Philips Semiconductors Application information 2.45 GHz power amplifier with the BFG480W COMPONENT LIST Table 2 Component list for the 2.45 GHz PA COMPONENT VALUE UNIT SIZE, MANUFACTURER PURPOSE, COMMENT TR1 BFG480W SOT343R Philips RF transistor TR2 BC817 SOT23 Philips NPN bias transistor R1 680 Ω 0.4 W metal film resistor R2 10 Ω 0.4 W metal film resistor R3 5 Ω 0.4 W metal film resistor C1 6.8 pF type 100A; see note 1 C2 2.2 pF type 100A; see note 1 C3 6.8 pF type 100A; see note 1 C4 1.2 pF type 100A; see note 1 C5 6.8 pF type 100A; see note 1 C6 6.8 pF type 100A; see note 1 C7 4.7 nF type 100A; see note 1 L1 4S2 µS1 − L = 18 mm; W = 0.25 mm micro stripline; Zo ≈ 100 Ω µS2 − L = 18 mm; W = 0.25 mm micro stripline; Zo ≈ 50 Ω µS3 − L = 18 mm; W = 0.25 mm micro stripline; Zo ≈ 50 Ω µS4 − L = 18 mm; W = 0.25 mm micro stripline; Zo ≈ 100 Ω PCB − ferroxcube chip bead εr ≈ 6.15; d = 0.64 mm Note 1. Multilayer ceramic chip capacitor; American Technical Ceramics or a capacitor of the same quality. 1999 Dec 03 5 Philips Semiconductors Application information 2.45 GHz power amplifier with the BFG480W BOARD LAYOUT The double copper-clad PFTE fibre-glass dielectric printed-circuit board has the following specification: • d = 0.64 mm • t = 35 µm (copper cladding thickness) • εr = 6.15 • tan δ = 0.0019 • Dimensions 35 × 45 mm. handbook, full pagewidth Vsupply R1 L1 TR2 R2 SOT343 R3 C7 C6 C3 µS1 µS4 C1 C5 µS2 µS3 C2 TR1 C4 output PH96076 input MGS764 Fig.2 PCB layout. 1999 Dec 03 6 Philips Semiconductors Application information 2.45 GHz power amplifier with the BFG480W MEASUREMENTS The measurements in the CW mode of operation have been done under the following conditions: • Supply voltage 3.0 V • Control voltage 3.0 V • Quiescent current 1 mA • Frequency 2.45 GHz. The output is optimized for an output level of 19 dBm. Table 3 Measuring results of the 2.45 GHz power amplifier ηPA (%) ηtot (%) Pi (dBm) Po (dBm) GP (dB) Isupply (mA) 0 6.40 6.40 15 7.48 9.70 1 8.80 7.80 19 11.10 13.31 2 10.90 8.90 24 14.89 17.09 3 12.70 9.70 28 19.79 22.17 4 14.30 10.30 34 23.92 26.39 5 15.80 10.80 41 28.34 30.91 6 17.10 11.10 48 32.85 35.62 7 18.20 11.20 56 36.34 39.33 8 19.00 11.00 64 38.09 41.37 9 19.80 10.80 73 39.98 43.61 10 20.50 10.50 83 41.04 45.06 11 21.10 10.10 94 41.22 45.68 12 21.60 9.60 103 41.65 46.78 13 22.20 9.20 113 43.07 48.96 14 22.70 8.70 126 42.62 49.26 15 23.10 8.10 135 42.61 50.41 16 23.40 7.40 140 42.61 52.09 17 23.70 6.70 142 43.26 55.03 18 23.90 5.90 144 42.22 56.82 19 24.20 5.20 146 41.92 60.05 20 24.30 4.30 149 37.84 60.21 1999 Dec 03 7 Philips Semiconductors Application information 2.45 GHz power amplifier with the BFG480W MGS765 12 P (dB) 10 handbook, G halfpage 45 ηPA 40 (%) (1) Po (dB) 35 30 8 (2) MGS766 30 handbook, halfpage 20 25 6 20 15 4 10 10 2 5 0 0 0 10 20 Po (dB) 0 30 0 4 8 12 20 16 Pi (dB) (1) Power gain GP. (2) Power added efficiency ηPA. Fig.3 Power gain and power added efficiency as a function of output power. 1999 Dec 03 Fig.4 Output power as a function of input power. 8