Philips Semiconductors Application Note Ultra Low Noise Amplifiers for 900 and 2000 MHz with High IP3 by Korné Vennema Philips Semiconductors Slatersville, RI December 1996 #KV96-157 This application note describes four Low Noise Amplifier designs with the BFG410W and the BFG425W, two devices from Philips Semiconductors’ fifth generation wideband technology. The amplifier designs include measurement results and pcb layouts. The following designs are included: a) 900 Mhz LNA with BFG410W b) 2 GHz LNA with BFG410W c) 900 Mhz LNA with BFG425W d) 2 Ghz LNA with BFG425W Introduction The substrate is connected directly to the emitter package lead, resulting in improved thermal performance (see figure 2). Today’s wireless applications require Low Noise Amplifiers with a high third order intercept point (IP3) and a low noise figure (NF) at the same time. This is particularly interesting for 1900 MHz CDMA receiver front ends. This report describes four ultra low noise amplifiers for 900 MHz and 1900 MHz wireless applications, using Philips Semiconductors’ fifth generation wideband technology. Philips’ fifth generation die technology uses a double polysilicon process with a buried layer which results in transition frequencies (fT) higher than 20 GHz, gains in excess of 20 dB and Noise Figures as low as 1.2 dB. The amplifiers are designed for use at 2 Volt collector emitter voltage. A separate paragraph describes ways to improve IP3 in a LNA. C short emitter E wire die E B Figure 2: Short emitter bonding wires reduce emitter inductance, which results in high gain. Heat flows through two emitter leads which lowers thermal resistance. Overall: Improved RF and thermal performance The types of the fifth generation The table below shows the three new types that use the fifth generation die technology. The fifth generation Philips’ fifth generation double poly silicon wideband technology (see figure 1) uses a steep emitter doped profile resulting in transition frequencies over 20 GHz, and with poly base contacts a low base resistance is obtained. Via the buried layer, the collector contact is brought out at the top of the die. Type IE ^ (mA) fT (GHz) BFG403W BFG410W BFG425W 3 10 25 17 22 24 MSG (dB) f=2GHz 22 23 21 NF (dB) f=2GHz 1.5 1.3 1.3 IP3, using bypassing to improve it Figure 1: transistor Double polysilicon Third order intercept point is usually determined by using a two tone test, i.e. two equal carriers with a small offset in frequency. Due to transistor nonlinearities, these two carriers generate distortion products, both in-band and out of band (see figure 3). The product f2-f1 is a low frequency product that is generated, which can modulate buried 2 frequency, i.e. either 900 or 1900 MHz. Adding additional bypassing by means d3 d3 R Cd 0 f2-f 1 2f1-f 2 f 1 f2 2f2-f1 C Figure 3: Two tone test and generated intermodulation distortion products. f2-f1 is the low frequency product C Out BFG4xx the base-emitter and collector-emitter voltages of a transistor used in an amplifier. This results in a fluctuating bias (base) voltage and supply (collector) voltage. For good linearity, a constant base and collector voltage are required. Lowering the collector voltage causes an amplifier to saturate earlier, thus decreasing linearity for a certain power level. The base voltage sets the quiescent current for the device, and thus the linearity (see also figure 4) . A fluctuating base voltage would change the linearity of the amplifier. Therefore it is important to apply proper bypassing at both collector and base. In Figure 5: Typical circuit diagram for a LNA. Cd is the additional bypassing for low frequencies. R is added to prevent low frequency instabilities. C is a short for the working frequency (27 pF at 900 MHz and 5.6 pF at 1900 MHz) of Cd improves the IP3 considerably. An improvement of 6 - 10 dB in IP3 can be expected. As a rule of thumb, the impedance of Cd should be smaller than 25 percent of the input impedance of the transistor at a particular carrier spacing. In case of a BFG520 (fourth generation wideband transistor) the following calculation is valid: IP3 (dBm) Zin (25kHz) ≈ hfe / gm = 120 / (40 * 0.0065) ≈ 450 Ω Cd < 0.25 * 450 ≈ 100 Ω At 25 kHz, the capacitor value equals: C d = 1 / (2 * π* f * 100) ≈ 63 nF IP3 deviation through bias decoupling Ic (mA) 63 nF is the minimum recommended value. It is obvious that a higher capacitor value does a better job. Space constraints often don’t allow the use of electrolytic (or even better tantalum) capacitors. In most cases, a 100 nF or 220 nF capacitor is sufficient. So far only base bypassing has been discussed. Similar effects can be Figure 4: IP3 in a Low Noise Amplifier is related to the collector current and also collector emitter voltage. As a rule of thumb for bipolar technology: IP3out=10 log (Vce * Ic * 5E3) in dBm Figure 5 shows the typical circuit diagram for a bipolar LNA. C is the bypassing capacitor for the working 3 R2* 120 Ω Better RF-stability (K>1). R3* 22 Ω RF-block. R4* 560 Ω Cancelling HFE-spread. R5** 100 Ω To improve IP3-performance C1* 2.2 pF Input match. C2* 27 pF 900MHz short. C3* 27 pF 900MHz short. C4* 1 nF RF-short C5* 1.5 pF Output match. C6** 100 nF To improve IP3-performance C7* 0.47 pF Better RF-stability (K>1). Coil_1 12 nH Input match. Coil_2 15 nH Output match. µs4 next table µ-stripline + via Board FR4: ε r =4.6, h=0.5 mm, t=35 µm * 0603 Philips * * 0805 Philips Coils: 0805CS Coilcraft expected when collector bypassing is also applied; however, the effects are less dramatic. a) 900 MHz LNA with BFG410W This section describes a 900 MHz LNA with the BFG410W. The performance can be summarized as follows: Vce=2V, Ic =2mA, VSUP≈3.3V freq. = 900MHz |S 21|2 = 14 dB |S 12|2 = -26 dB NF = 1.4 dB VSWRi = 1 : 1.9 VSWRo = 1 : 2.3 IP3in = -9 dBm (∆f=100 kHz) C6 R5 C3 C2 R1 µS4 Emitter inductance (µ-stripline + via): 2.0mm µ-stripline Z0~48Ω (PCB: ε r ~4.6, H=0.5mm) L2 L3 W1 W2 D1 1.0mm 1.0mm 0.5mm 1.0mm 0.4mm Emitter inductance: µ-stripline via-hole Table 1: 900 MHz LNA with BFG410W, List of components. C4 R3 L1 R4 C1 RFin +V sup C7 C5 R5 C6 Coil_2 Coil_1 R2 50 Ω In RFout L1 R2 C5 50 Ω Out C1 C2 C7 C4 R1 L2 Vsup W1 R4 BFG410W µS4: L2 µ S4 µS4 D1 L3 W2 Figure 6: Schematic diagram 900 MHz LNA with BFG410W. Input and output matching is realized with a LC combination. Additional emitter inductance on both emitter leads is used to improve the matching. All resistors and capacitors are 0603 or 0805 Philips SMD components. Coils are Coilcraft 0805. Board material is FR4. Comp.: Value: Comment: R1* 47 Bias. kΩ R3 C3 Figure 7: PCB-layout 900 MHz LNA with BFG410W. L1 4 b) 2 GHz LNA with BFG410W R1 47 KΩ Bias. R2 10 Ω Better RF-stability (K>1). R3 22 Ω RF-block. R4 560 Ω Cancelling HFE-spread. C1 1 pF Input match. C2 5.6 pF 2GHz short. C3 5.6 pF 2GHz short. C4 1 nF RF-short C5 3.3 pF Output match. C7 0.47 pF Better RF-stability (K>1). µs1 W=0.25mm µ-stripline Z0~95Ω µs2 W=0.25mm µ-stripline Z0~95Ω µs3 W=0.25mm µ-stripline Z0~95Ω µs4 (next table) µ-stripline + via Board FR4: ε r =4.6, h=0.5 mm, t=35 µm All resistors and capacitors 0603 Philips This paragraph describes a 2 GHz LNA with the BFG410W. The performance can be summarized as follows: Vce=2V, Ic =2mA, VSUP≈3.3V freq. = 2 GHz |S 21|2 = 14.3 dB |S 12|2 = -30 dB NF = 1.7 dB VSWRi = 1 : 2.1 VSWRo = 1 : 2.1 µS4 Emitter inductance (µ-stripline + via): C3 C2 C4 R1 R3 +V sup R4 µS3 µS1 R2 50 Ω In L1 L2 L3 W1 W2 D1 µS2 C1 2.0mm 1.0mm 1.0mm 0.5mm 1.0mm 0.4mm µ-stripline Z0~48Ω Emitter inductance: µ-stripline via-hole Table 2: 2 GHz LNA with BFG410W, List of components. 50 Ω Out C5 C1 RFin C7 C7 W1 BFG410W µS4: L1 R2 L2 µS4 µ S4 D1 L3 RFout W2 R1 C5 C2 Figure 8: Schematic diagram 2 GHz LNA with BFG410W. C3 Vsup R3 R4 C4 Input and output matching is realized with a microstrip-C combination. Additional emitter inductance on both emitter leads is used to improve the matching to 50 Ω. All resistors and capacitors are 0603 Philips SMD components. Coils are Coilcraft 0805. Board material is FR4. Figure 9: PCB-layout 2 BFG410W. Please note that this amplifier is not optimized for noise and IP3 (extra bypassing is missing) Comp Value: GHz LNA with c) 900 MHz LNA with BFG425W Comment: 5 W1 W2 D1 This section describes a 900 MHz LNA with the BFG425W. The performance can be summarized as follows: Table 3: 900 MHz LNA with BFG425W, List of components. Vce=2V, Ic =10mA, VSUP≈3.7V freq. = 900MHz |S 21|2 = 17.3 dB NF = 1.7 dB VSWRi = 1 : 2.5 VSWRo = 1 : 1.8 IP3in = +3 dBm (∆f=200 kHz) C6 C3 C2 R1 Input and output matching is realized with a microstrip-C combination. Additional emitter inductance on both emitter leads is used to improve the matching to 50 Ω. All resistors and capacitors are 0603 or 0805 Philips SMD components. Coils are Coilcraft 0805. Board material is FR4. C4 R3 R4 +Vsup Coil_1 R2 width µ-stripline width via-hole area diameter of via-hole 0.5mm 1.0mm 0.4mm C1 RFin Coil_2 C5 C7 50 Ω Out C1 50 Ω In C5 RFout C6 L1 R2 C2 C7 C4 R1 L2 W1 Vsup BFG425W µS4: L1 R4 L2 µS4 µS4 D1 Figure 10: Schematic diagram 900 MHz LNA with BFG425W. Comp Value Purpose, comment R1* 8.2 kΩ Bias (coll.-base) R2* 10 Ω better S22 and stability R3* 22 Ω RF blocking R4* 150 Ω cancelling hFE spread C1* 8.2 pF Input match (input to base) C2* 27 pF 900 MHz short (L1 to ground) C3* 27 pF 900 MHz short (L2 to ground) C4** 100 nF RF decoupling collector bias C5* 22 pF Output match C6** 100 nF To improve IP3 C7* 3.3 pF Output match, stability Coil_1 22 nH Input match (base-bias) Coil_2 12 nH Output match (collector-bias) µs4 next table µ-stripline Emitter-inductance Board FR4: εr=4.6, h=0.5 mm, t=35µm * = 0603 Philips ** = 0805 Philips Coils: 0805CS Coilcraft µS4 Emitter inductance of µ-stripline and via-hole Dimension 2.5mm 1.0mm L3 1.0mm C3 Figure 11: PCB-layout 900 MHz LNA with BFG425W. W2 Name L1 L2 R3 L3 Description length µ-stripline; Z0~48Ω length interconnect stripline and viahole area length via-hole area 6 d) 2 GHz LNA with BFG425W Comp Value: Comment: R1* 15 KΩ Bias. R2* 0 Ω Omitted. R3* 22 Ω RF-block. R4* 82 Ω Cancelling HFE-spread. R5** 100 Ω To improve IP3-performance C1* 4.7 pF Input match. C2* 5.6 pF 2GHz short. C3* 5.6 pF 2GHz short. C4* 1 nF RF-short C5* 2.7 pF Output match. C6** 100 nH To improve IP3-performance µs1 8.9 x 0.25mm µ-stripline Z0~95Ω µs2 3.9 x 0.25mm µ-stripline Z0~95Ω µs3 6.6 x 0.25mm µ-stripline Z0~95Ω µs4 (next table) µ-stripline + via Board FR4: ε r =4.6, h=0.5 mm, t=35 µm * 0603 Philips * * 0805 Philips This section describes a 2 GHz LNA with the BFG425W. The performance, for different collector currents can be summarized as follows: IC [mA] |S21|2 [dB] VCE ~ 2.5V 2GH z 2 3 5 6 8 10 14.4 15.9 16.3 16.6 16.9 17.1 IP3_ A [dBm ] input IP3_ B [dBm ] input -10.9 -3.4 -0.9 1.0 3.9 6.5 -2.3 -0.4 1.8 2.6 5.6 6.7 NF [dB] 2 GHz 1.5 1.7 1.8 1.9 2.1 2.3 µS4 Emitter induction (µ-stripline + via): L1 L2 L3 W1 W2 D1 µ-stripline Z0~48Ω 1.0mm 1.0mm 1.0mm 0.5mm 1.0mm 0.4mm Emitter inductance µ-stripline via-hole Table 4: Performance summary 2 GHz LNA with BFG425W Table 5: 2 GHz LNA with BFG425W, List of components. Input and Output VSWR is in all cases better than 1 : 2. IP3_A is the third order intercept without R5 and C6. IP3_B is the third order intercept with R5 and C6. It can be noticed that the IP3 improvement becomes less effective when the collector current increases. Input and output matching is realized with a microstrip-C combination. Additional emitter inductance on both emitter leads is used to improve the matching to 50 Ω. All resistors and capacitors are 0603 or 0805 Philips SMD components. Coils are Coilcraft 0805. Board material is FR4. C6 R5 C1 C3 C2 R1 RFin R3 C6 µS3 R2 50 Ω In R2 +V sup R4 µS1 µS2 C1 BFG425W C4 50 Ω Out RFout R1 R5 C5 C2 C7 W1 BFG425W µS4: Vsup L1 µ S4 D1 C3 R3 R4 L2 µS4 C5 L3 Figure 13: PCB-layout 2 GHz LNA with BFG425W. W2 CONCLUSION Figure 12: Schematic diagram 2 GHz LNA with BFG425W. 7 High performance small size LNAs, with a low supply voltage and current can be made with the new Philips BFG400W series double polysilicon transistors. IP3 can be optimized with extra components, and/or by increasing IC. Increasing voltage also improves the IP3 point. The LNAs presented in this brief application note are not the most optimized designs, nor are shown all possible circuit configurations by any means . They only show some possible LNA-designs with the BFG400W series double polysilicon transistors. 8