AN10945 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 Rev. 01 — 18 November 2010 Application note Document information Info Content Keywords BLF881, DVB-T, VHF, ACPR, LDMOS, power amplifier, linearity, efficiency, gain flatness, peak power Abstract This application note describes the design and performance of a 50 W DVB-T power amplifier for the 174 MHz to 230 MHz VHF band using the BLF881 power transistor. In particular, it compares the DVB-T performance for flat gain with best ACPR tuning. AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 Revision history Rev Date Description 1 20101118 Initial version Contact information For more information, please visit: http://www.nxp.com For sales office addresses, please send an email to: [email protected] AN10945 Application note All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 2 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 1. Introduction The BLF881 is a 50 V high power RF transistor based on NXP Semiconductor’s high voltage LDMOS process. It is designed for use in the 470 MHz to 860 MHz UHF broadcast band, where it can deliver 140 W (peak sync) for analog TV and 33 W for DVB-T (8K). When using the BLF881 in the VHF band, special attention is needed to achieve a broadband input match due to the high Q (6 at 174 MHz) at these lower input frequencies. With care, an input return loss better than 6 dB can be achieved across the 28 % fractional bandwidth. Another issue at VHF frequencies is that the load pull contours for power, gain and efficiency are all relatively steep and distinct from each other, so the designer has to make significant trade-offs between linearity, efficiency and gain flatness for a broadband output network. In this design, we compare two differently tuned outputs: • Flat gain: where gain flatness is optimized over the band while balancing peak power at the band top and bottom, but sacrificing efficiency. • Best ACPR: where ACPR and efficiency are optimized over the band, while balancing efficiency at the band top and bottom, but sacrificing gain flatness. 019aaa401 Output tuned for best ACPR. Fig 1. The assembled DVB-T BLF881 amplifier AN10945 Application note All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 3 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 2. Test summary The amplifier was characterized under the conditions shown in Table 1. Table 1. RF performance summary Characteristic AN10945 Application note Output tuned for Flat gain Best ACPR Frequency range 174 MHz to 230 MHz 174 MHz to 230 MHz Drain-Source voltage (VDS) 50 V 50 V Quiescent drain current (IDq) 0.5 A 0.5 A Minimum input return loss 6 dB 6 dB Peak DVB-T power no CCDF data 55.2 dBm to 55.4 dBm Peak pulse power at 202 MHz 53.4 dBm 52.4 dBm ACPR at PL = 40 W −24 dB to −34 dB −30 dB to −32 dB DVB-T drain efficiency (ηD) at PL = 40 W 23 % to 29 % 30 % to 37 % Peak pulse efficiency at 202 MHz 50 % 63 % Minimum gain at PL = 40 W 30.5 dB 28.1 dB Gain flatness 1.4 dB 5.9 dB All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 4 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 3. Design methodology Initial input tuning was determined with an Agilent Advanced Design System (ADS) using the equivalent input circuit provided for UHF applications. When the amplifier did not tune as predicted by this model, it was found that the equivalent circuit was not accurate at lower frequencies. To more accurately model the device input impedance, ADS was used to measure the input impedance of the non-linear BLF881 model in a large-signal harmonic balance simulation. This modelled impedance data was then used to more accurately model the tuning of the amplifier’s input network. The modelled input impedance data is shown in Table 2. Table 2. Modelled input impedance (Zi) Pi = 10 dBm, ZL = 4 + j0 Ω, VDS = 50 V, IDq = 0.5 A. Frequency Zi 170 MHz 1.2 − j7.2 Ω 200 MHz 1.2 − j6.1 Ω 230 MHz 1.2 − j5.3 Ω The optimal load impedance was determined by a load pull analysis using ADS. The compromise load points were chosen to favour peak power, followed by efficiency, while ignoring gain flatness. A load impedance of 4 + j0 Ω across the band met these criteria. The tuning of the output was then determined for this 4 Ω load impedance using a linear small-signal analysis. The 56 pF capacitors used to short-circuit the second harmonic were also determined using this analysis. The resulting output network needed only minor tuning to deliver the best ACPR results as shown in this application note. The flat gain tuned output was determined by iterative tuning after examination of the load pull data to see which way the load impedance had to move across the band. AN10945 Application note All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 5 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 4. RF performance 4.1 Best ACPR tuning 019aaa402 35 G (dB) 33 0 shoulder distance (dB) −10 (1) −20 31 (2) 29 −30 (3) −40 27 25 170 190 −50 230 210 f (MHz) VDS = 50 V; IDq = 0.5 A; DVB-T = 8K (OFDM); ACPR measured within 30 kHz bandwidth at fc = ± 4.3 MHz. (1) Gain. (2) Lower adjacent. (3) Upper adjacent. Fig 2. AN10945 Application note DVB-T gain and ACPR at PL = 40 W All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 6 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 019aaa403 0 shoulder distance (dB) −10 50 ηD (%) (1) (2) (3) 40 −20 30 −30 20 −40 −50 10 (4) (5) (6) 0 0 20 40 60 80 PL (W) VDS = 50 V; IDq = 0.5 A; DVB-T = 8K (OFDM); ACPR measured within 30 kHz bandwidth at fc = ± 4.3 MHz. (1) ηD = 202 MHz. (2) ηD = 174 MHz. (3) ηD = 230 MHz. (4) ACPR = 174 MHz. (5) ACPR = 202 MHz. (6) ACPR = 230 MHz. Fig 3. DVB-T ACPR and drain efficiency 019aaa404 35 G (dB) 40 ηD (dB) (1) 33 36 (2) 31 32 29 28 27 24 25 170 190 20 230 210 f (MHz) VDS = 50 V; IDq = 0.5 A; DVB-T = 8K (OFDM). (1) Gain. (2) Drain efficiency. Fig 4. AN10945 Application note DVB-T gain and drain efficiency at PL = 40 W All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 7 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 019aaa405 9 PAR (dB) 50 ηD (%) (1) 8 40 (2) 7 30 6 170 190 20 230 210 f (MHz) VDS = 50 V; IDq = 0.5 A; DVB-T = 8K (OFDM); PAR at 0.01 % probability on the CCDF. (1) PAR. (2) Drain efficiency. Fig 5. DVB-T PAR and drain efficiency at PL = 50 W 019aaa406 34 80 ηD (%) G (dB) 32 60 (1) 30 40 28 20 (2) 26 0 34 38 42 46 50 54 PL (dBm) VDS = 50 V; IDq = 0.5 A; tp = 12 μs. (1) Gain. (2) Drain efficiency. Fig 6. AN10945 Application note Pulse gain and drain efficiency at 202 MHz All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 8 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 019aaa407 0 IRL (dB) −4 −8 −12 −16 −20 100 140 180 220 260 300 f (MHz) VDS = 50 V; IDq = 0.5 A; Pi = 10 dBm. Fig 7. Input return loss 4.2 Flat gain tuning 019aaa408 35 G (dB) 40 PAE (%) 33 36 (1) 31 32 29 28 (2) 27 25 170 24 190 20 230 210 f (MHz) VDS = 50 V; IDq = 0.5 A; DVB-T = 8K (OFDM). (1) Gain. (2) PAE. Fig 8. AN10945 Application note DVB-T gain and power added efficiency at PL = 40 W All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 9 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 019aaa409 0 shoulder distance (dB) −10 50 PAE (%) 40 −20 (1) −30 (2) 30 20 (3) −40 −50 10 0 0 20 40 60 80 PL (W) VDS = 50 V; IDq = 0.5 A; DVB-T = 8K (OFDM); ACPR measured within 30 kHz bandwidth at fc = ± 4.3 MHz. (1) Efficiency. (2) Upper adjacent. (3) Lower adjacent. Fig 9. DVB-T ACPR and power added efficiency at 202 MHz 019aaa410 32 60 ηD (%) G (dB) (1) 30 40 28 20 (2) 26 0 34 38 42 46 50 54 PL (dBm) VDS = 50 V; IDq = 0.5 A; tp = 12 μs. (1) Gain. (2) Drain efficiency. Fig 10. Pulse gain and drain efficiency at 202 MHz Note that the peak power with flat gain tuning is up to 0.5 dB higher than with best ACPR tuning. Linearity (evident with poorer ACPR and more gain expansion with power) and efficiency are both significantly worse with flat gain tuning. A more suitable approach to AN10945 Application note All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 10 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 achieving flat gain than tuning the output is probably to use a simple gain slope network at the amplifier input. A frequency-selective lossy network could also be used to improve input return loss across the band. The flat gain tuning was achieved with C8 = 2 × 68 pF (ATC 800B) mounted 33 mm from the start of the 4 mm output microstrip (compared to 82 pF and 41 mm, for best ACPR tuning) and C9 = 33 pF (compared to 30 pF for best ACPR tuning). 5. PCB and schematic The PCB was designed to accommodate either the BLF881 or the BLF573, a 300 W LDMOS RF power transistor designed for broadcast applications and industrial, scientific and medical applications in the HF to 500 MHz band. 019aaa411 PCB is a Rogers 5880, height = 0.79 mm, copper thickness = 35 μm. Fig 11. PCB layout AN10945 Application note All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 11 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 Table 3. Bill of Materials Component Description Value Remarks C1, C21 capacitor; 100 V 5 % NPO; 0805 1 nF ATC 800R C2 capacitor; 100 V 5 % NPO; 0805 18 pF ATC 100B C3, C4, C5 capacitor; 100 V 5 % NPO; 0805 100 pF - C6, C7 capacitor; 500 V 5 % NPO 56 pF - C8 capacitor; 500 V 5 % NPO 82 pF - C9 capacitor; 500 V 5 % NPO 30 pF - C10, C31 capacitor; 500 V 5 % NPO 510 pF - C20, C25, C30, C34, C37 capacitor; 250 V 5 % NPO; 1210 10 nF - C22, C27 capacitor; 25 V 10 % X7R; 1206 10 μF - C23, C26 capacitor; 50 V 10 % X7R; 0805 100 nF - C24 capacitor; 25 V 10 % X7R; 0805 1 μF - C32 capacitor; 100 V 10 % X7R; 1210 100 nF - C33 capacitor; 100 V 10 % X7S; 2220 10 μF TDK C5750X7S2A106M C35 capacitor; 100 V 10 % X7R; 1206 1 μF TDK C3216X7R2A105K C36 capacitor; 63 V aluminium electrolytic 470 μF - L1 inductor; 5t; air 18.5 nH Coilcraft A05T L2, L5 ferrite bead; 5 A 45 Ω at 100 MHz Fair-Rite 2743019447 L3 inductor; 3t; 20 AWG; 3 mm; ID - - L4 inductor; 4t; 20 AWG; 4 mm; ID - - R1, R2 resistor; 5 %; 100 ppm; CF; 0805 2.2 Ω - E1, E2 tab; Faston; 0.25 inch - - ferrite bead; 200 mA; 0805 1 k Ω at 100 MHz - C101, C102, C105 capacitor; 50 V 10 % X7R; 0805 100 nF - C106 capacitor; 100 V 5 % NPO; 0805 1 nF - C103, C104, C107 capacitor; 50 V 10 % X7R; 0805 1 μF - C108 capacitor; 100 V 10 % X7R; 1210 2.2 μF - D101 LED; green; 1206 - - D102 LED; red; 1206 - - U101 voltage regulator - Linear LT3010EMS8E U102 dual comparator - Linear LT6700CS6-3 Q101 transistor NPN; 45 V; 100 mA; GP - NXP BC847B U103 rail-rail opamp - National LM7321MF R106 potentiometer; 5t cermet 200 Ω - R3, R4 resistor; 5 %; 100 ppm; CF; 2010 1Ω positioned under L4 R112, R113, R117, R118 resistor; 1 %; 100 ppm; CF; 0805 10 kΩ - R104, R114, R115 resistor; 1 %; 100 ppm; CF; 0805 1.1 kΩ - R105 resistor; 1 %; 100 ppm; CF; 0805 2 kΩ - RF circuit Bias circuit L101, L102 AN10945 Application note All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 12 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 Table 3. Bill of Materials Component Description Value Remarks R102, R103, R108 resistor; 1 %; 100 ppm; CF; 0805 432 Ω - R116 resistor; 1 %; 100 ppm; CF; 0805 52.3 kΩ - R109 resistor; 1 %; 100 ppm; CF; 0805 5.11 kΩ - R101 resistor; 1 %; 100 ppm; CF; 0805 0.0 Ω - R111 resistor; 1 %; 100 ppm; CF; 0805 88.7 kΩ - R110 resistor; 1 %; 100 ppm; CF; 0805 909 Ω - E101, E102 test point - - AN10945 Application note All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 13 of 17 xxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxx x x x xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxx xx xx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxx xxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxx x x xxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxx xxx NXP Semiconductors AN10945 Application note VD L101 BLM21BD102 VG U101 LT3010EMS8E IN EN 1 5 2 +8V OUT ADJ R116 52.3 kΩ GND:4,9 C106 1 nF C107 1 μF R103 432 Ω bias monitor/overdrive E102 R115 1.1 kΩ R102 432 Ω C108 2.2 μF R104 1.1 kΩ R117 10 kΩ R106 200 Ω R105 2 kΩ D101 HSMG-C150 green = power R101 75 Ω U103 LM7321MF 3 5 C101 100 nF R108 R113 432 Ω 10 KΩ R111(1) 88.7 kΩ R109 5.1 kΩ 1 4 C102 100 nF 3 3 Q101 BC847B 5 R114(1) 1.1 kΩ 400 mV C105(1) 100 nF R112(1) 10 kΩ ground E101 C104 1 μF D102(1) HSMH-C150 red = overtemp 2 LT6700CS6-3 U102(1) 019aaa412 AN10945 14 of 17 © NXP B.V. 2010. All rights reserved. Fig 12. Bias circuit schematic VGATE 6 4 (1) These components are optional. 1 2 1 2 R110 909 Ω C103 1 μF 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 Rev. 01 — 18 November 2010 All information provided in this document is subject to legal disclaimers. R118 10 kΩ 8 L102 BLM21BD102 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 6. Abbreviations Table 4. AN10945 Application note Abbreviations Acronym Description ACPR Adjacent Channel Power Ratio CCDF Complementary Cumulative Distribution Function DVB-T Digital Video Broadcast - Terrestrial LDMOS Laterally Diffused Metal-Oxide Semiconductor OFDM Orthogonal Frequency Division Multiplex PAE Power Added Efficiency PAR Peak-to-Average power Ratio PCB Printed-Circuit Board All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 15 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 7. Legal information 7.1 Definitions Draft — The document is a draft version only. The content is still under internal review and subject to formal approval, which may result in modifications or additions. NXP Semiconductors does not give any representations or warranties as to the accuracy or completeness of information included herein and shall have no liability for the consequences of use of such information. 7.2 Disclaimers Limited warranty and liability — Information in this document is believed to be accurate and reliable. However, NXP Semiconductors does not give any representations or warranties, expressed or implied, as to the accuracy or completeness of such information and shall have no liability for the consequences of use of such information. In no event shall NXP Semiconductors be liable for any indirect, incidental, punitive, special or consequential damages (including - without limitation - lost profits, lost savings, business interruption, costs related to the removal or replacement of any products or rework charges) whether or not such damages are based on tort (including negligence), warranty, breach of contract or any other legal theory. Notwithstanding any damages that customer might incur for any reason whatsoever, NXP Semiconductors’ aggregate and cumulative liability towards customer for the products described herein shall be limited in accordance with the Terms and conditions of commercial sale of NXP Semiconductors. Right to make changes — NXP Semiconductors reserves the right to make changes to information published in this document, including without limitation specifications and product descriptions, at any time and without notice. This document supersedes and replaces all information supplied prior to the publication hereof. Suitability for use — NXP Semiconductors products are not designed, authorized or warranted to be suitable for use in life support, life-critical or safety-critical systems or equipment, nor in applications where failure or malfunction of an NXP Semiconductors product can reasonably be expected to result in personal injury, death or severe property or environmental damage. NXP Semiconductors accepts no liability for inclusion and/or use of NXP Semiconductors products in such equipment or applications and therefore such inclusion and/or use is at the customer’s own risk. Applications — Applications that are described herein for any of these products are for illustrative purposes only. NXP Semiconductors makes no representation or warranty that such applications will be suitable for the specified use without further testing or modification. Customers are responsible for the design and operation of their applications and products using NXP Semiconductors products, and NXP Semiconductors accepts no liability for any assistance with applications or customer product AN10945 Application note design. It is customer’s sole responsibility to determine whether the NXP Semiconductors product is suitable and fit for the customer’s applications and products planned, as well as for the planned application and use of customer’s third party customer(s). Customers should provide appropriate design and operating safeguards to minimize the risks associated with their applications and products. NXP Semiconductors does not accept any liability related to any default, damage, costs or problem which is based on any weakness or default in the customer’s applications or products, or the application or use by customer’s third party customer(s). Customer is responsible for doing all necessary testing for the customer’s applications and products using NXP Semiconductors products in order to avoid a default of the applications and the products or of the application or use by customer’s third party customer(s). NXP does not accept any liability in this respect. Export control — This document as well as the item(s) described herein may be subject to export control regulations. Export might require a prior authorization from national authorities. Evaluation products — This product is provided on an “as is” and “with all faults” basis for evaluation purposes only. NXP Semiconductors, its affiliates and their suppliers expressly disclaim all warranties, whether express, implied or statutory, including but not limited to the implied warranties of non-infringement, merchantability and fitness for a particular purpose. The entire risk as to the quality, or arising out of the use or performance, of this product remains with customer. In no event shall NXP Semiconductors, its affiliates or their suppliers be liable to customer for any special, indirect, consequential, punitive or incidental damages (including without limitation damages for loss of business, business interruption, loss of use, loss of data or information, and the like) arising out the use of or inability to use the product, whether or not based on tort (including negligence), strict liability, breach of contract, breach of warranty or any other theory, even if advised of the possibility of such damages. Notwithstanding any damages that customer might incur for any reason whatsoever (including without limitation, all damages referenced above and all direct or general damages), the entire liability of NXP Semiconductors, its affiliates and their suppliers and customer’s exclusive remedy for all of the foregoing shall be limited to actual damages incurred by customer based on reasonable reliance up to the greater of the amount actually paid by customer for the product or five dollars (US$5.00). The foregoing limitations, exclusions and disclaimers shall apply to the maximum extent permitted by applicable law, even if any remedy fails of its essential purpose. 7.3 Trademarks Notice: All referenced brands, product names, service names and trademarks are the property of their respective owners. All information provided in this document is subject to legal disclaimers. Rev. 01 — 18 November 2010 © NXP B.V. 2010. All rights reserved. 16 of 17 AN10945 NXP Semiconductors 174 MHz to 230 MHz DVB-T power amplifier with the BLF881 8. Contents 1 2 3 4 4.1 4.2 5 6 7 7.1 7.2 7.3 8 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Test summary. . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Design methodology . . . . . . . . . . . . . . . . . . . . . 5 RF performance . . . . . . . . . . . . . . . . . . . . . . . . . 6 Best ACPR tuning. . . . . . . . . . . . . . . . . . . . . . . 6 Flat gain tuning . . . . . . . . . . . . . . . . . . . . . . . . . 9 PCB and schematic . . . . . . . . . . . . . . . . . . . . . 11 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Legal information. . . . . . . . . . . . . . . . . . . . . . . 16 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Disclaimers . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Trademarks. . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Please be aware that important notices concerning this document and the product(s) described herein, have been included in section ‘Legal information’. © NXP B.V. 2010. All rights reserved. For more information, please visit: http://www.nxp.com For sales office addresses, please send an email to: [email protected] Date of release: 18 November 2010 Document identifier: AN10945