APPLICATION INFORMATION 2.4 GHz low noise amplifier with the BFG480W Philips Semiconductors Application information 2.4 GHz low noise amplifier with the BFG480W ABSTRACT • Description of the product The BFG480W is one of the Philips double polysilicon wideband transistors of the BFG400 series. • Application area Low voltage high frequency wireless applications. • Presented application A low noise amplifier for 2.4 GHz applications such as wireless local area network and wireless local loop. • Main results At a frequency of 2.4 GHz, the amplifier has an insertion power gain of approximately 9.5 dB, a noise figure of approximately 3 dB, and a third order intercept point of approximately 17 dBm (measured at input). 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 22 2 Philips Semiconductors Application information 2.4 GHz low noise amplifier with the BFG480W INTRODUCTION With the Philips double polysilicon wideband transistor BFG480W, it is possible to design Low Noise Amplifiers (LNAs) for high frequency applications with a low current and a low supply voltage. These amplifiers are well suited for the new generation low voltage high frequency wireless applications. One feature of the BFG480W is that it has a good linearity performance. Therefore the BFG480W is well suited for LNAs with high linearity demands, such as Code Division Multiple Access (CDMA) systems. This application note gives an example of a 2.4 GHz LNA with the BFG480W. Because this LNA design has a high third order intercept value of 17 dBm (measured at input), it can be used for Wireless Local Area Network (WLAN) front-end and Wireless Local Loop (WLL) applications. CIRCUIT DESCRIPTION The following initial conditions apply for the amplifier design: • Vsupply ≈ 3.6 V • VCE = 2 V • IC = 40 mA • f = 2.4 GHz. The circuit is designed to show the following performance: • s212 ≈ 9 dB • VSWRIN < 2 • VSWROUT < 2 • NF ≤ 3.5 dB • IP3i > 15 dBm. The output matching is realised with an LC combination. Also an extra emitter inductance (micro stripline) is used on both emitter-leads to improve the matching and the noise figure. CIRCUIT DIAGRAM R2 handbook, full pagewidth Vsupply C3 C2 R1 input 50 Ω C4 L1 output 50 Ω W1 C1 TR1 µS1, µS2: L1 L2 µS1 µS2 MGS628 Fig.1 Circuit diagram. 1999 Dec 22 L3 D1 3 W2 Philips Semiconductors Application information 2.4 GHz low noise amplifier with the BFG480W COMPONENT LIST Table 1 Component list for the 2.4 GHz LNA COMPONENT VALUE TR1 BFG480W R1 2.7 UNIT kΩ SIZE, MANUFACTURER PURPOSE, COMMENT SOT343R Philips RF transistor 0603 Philips collector to base bias R2 39 Ω 0603 Philips collector series bias; levelling hFE spread C1 5.6 pF 0603 Philips input match (base coupling) C2 3.3 pF 0603 Philips output match (collector coupling) C3 5.6 pF 0603 Philips 2.4 GHz short (L1 to ground) C4 1 nF 0603 Philips RF collector bias decoupling L1 150 nH 0805CS Coilcraft µS1 see Table 2 emitter induction: micro stripline and via-hole µS2 see Table 2 emitter induction: micro stripline and via-hole PCB FR4 εr ≈ 4.6, d = 0.5 mm Table 2 output match Dimensions of the micro striplines µS1 and µS2 (see Fig.1) DIMENSION VALUE UNIT DESCRIPTION L1 1.0 mm length micro stripline; Zo ≈ 48 Ω L2 1.0 mm length interconnect micro stripline and via-hole area L3 1.0 mm length via-hole area W1 0.5 mm width micro stripline W2 1.0 mm width via-hole area D1 0.4 mm diameter of via-hole 1999 Dec 22 4 Philips Semiconductors Application information 2.4 GHz low noise amplifier with the BFG480W BOARD LAYOUT Short-circuit wires are used to adapt an existing printed-circuit board, which was developed for low noise applications. The layout has been designed with the Hewlett Packard Microwave Design System (HP-MDS). handbook, full pagewidth input C1 µS2 output C2 TR1 R1 Vsupply C4 L1 µS1 R2 C3 MGS629 Fig.2 PCB layout. MEASUREMENTS The measurements have been done under the following conditions (unless otherwise specified): • Supply voltage 3.6 V • Supply current 40 mA • Frequency 2.4 GHz. Table 3 Measuring results of the 2.4 GHz LNA SYMBOL PARAMETER CONDITION VALUE UNIT s212 insertion power gain 9.6 VSWRIN input voltage standing wave ratio 1.6 VSWROUT output voltage standing wave ratio 1.6 NF noise figure 3.0 dB IP3i third order intercept point 17 dBm 1999 Dec 22 Pi = −10 dBm; ∆f= 200 kHz 5 dB