AN2048 Application note PD54008L-E: 8 W - 7 V LDMOS in PowerFLAT packages for wireless meter reading applications Introduction STMicroelectronics has been strongly involved in finding new package solutions for power integrated circuits to obtain a surface mount device (SMD). The PowerFLAT™ package introduced in this application note shows the new concept of chip-size packaging representing a fundamental step to reduce the costs of assembly and to shrink power amplifier modules. This package helps maximize board space with improved electrical and thermal performances over traditional packages with leads. This leadless package is an MLP (micro leadframe package) where the electrical connections are made through landing pads on the bottom surface of the component. These landing pads are soldered directly to the pc board. Figure 1. MLP cross section Figure 2. Intermodulation distortion versus peak effective output power The standard MLP has an exposed die attach pad which enhances the thermal and electrical characteristics enabling high-power and high-frequency applications. For small and medium-power applications, such as wireless PMR (private mobile radio) LDMOS (Laterally Diffused MOS) transistors in PowerFLAT packages offer certain advantages compared to equivalent bipolar transistors, for example, better intermodulation (IMD3). Under certain conditions, an LDMOS transistor exhibits better intermodulation distortion than a bipolar junction transistor. Figure 2 shows intermodulation distortion versus peak effective output power for equivalently rated bipolar and LDMOS transistors. As we can see, below 30 W, the LDMOS device has lower intermodulation distortion than the bipolar transistor. ● Good gain linearity ● Smooth saturation ● Simpler bias circuit ● Thermal stability. The drain current has a positive temperature coefficient, therefore the MOS transistor is not susceptible to thermal runaway. ● Better ruggedness February 2008 Rev 2 1/13 www.st.com Contents AN2048 Contents 1 Basic wireless meter reading system description . . . . . . . . . . . . . . . . . 4 2 Electrical requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Circuit design and considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1 Amplifier construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Circuit schematic and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Transmission line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1 Characterization results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6 Components layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7 Characterization results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8 Feature characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2/13 AN2048 List of figures List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. MLP cross section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Intermodulation distortion versus peak effective output power . . . . . . . . . . . . . . . . . . . . . . . 1 Network system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Source and load impedances of PD54008L-E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Device footprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Cross section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Broadband power amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Transmission line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Power gain vs. frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Input return loss vs. frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Drain efficiency vs. frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Drain efficiency vs. frequency at different drain voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Power out vs. drain voltage at different frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Impedance data schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 PD54008L-E amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3/13 Basic wireless meter reading system description 1 AN2048 Basic wireless meter reading system description To reduce cost and difficulties associated with the reading of indoor utility meters for gas, water and electricity, a new automatic meter reading system has recently been introduced. It uses radio frequency networks and allows direct data communication between reading meters and services and/or the billing department. A DTU (Data Transmission Unit) module that contains a powerful UHF narrow-band radio transmitter is attached to gas, water and electric utility meters. Figure 3. Network system A DCU (Data Collector Unit) is placed in a convenient location within an apartment building or housing complex. The DCU contacts daily an NCC (Network Control Computer) and forwards the meter reading information. The NCC processes the information and provides billing data and customer support information. This paper describes a DTU solution using an STMicroelectronics 8 W - 7 V LDMOS device housed in a PowerFLAT and called PD54008L-E. 2 4/13 Electrical requirements ● VDD=5 V IDQ = 10 mA frequency band [450 ÷ 470] MHz ● Pout = 36 dBm gain flatness < 1dB AN2048 3 Circuit design and considerations Circuit design and considerations The PD54008L-E is an 8 W - 7 V LDMOS housed in a PowerFLAT plastic package (5x5 mm). Being an internally unmatched device, the PD54008L-E can be used in different portable applications over HF, VHF & UHF frequency bands. Table 1 shows the source and load impedances of the PD54008L-E at 500 MHz. Figure 4. Source and load impedances of PD54008L-E Table 1. Source and load impedances of PD54008L-E at 500 MHz F (MHz) Z1 (Ω) Z2 (Ω) 500 0.3+j2.0 1.8+j0.7 The above impedances are taken as a starting point to design the input and output matching networks of the PD54008L-E amplifier. Microstrip lines and lumped elements are used. 3.1 Amplifier construction The PCB is made of double-sided copper-clad fiberglass (THK 0.020") with the lowest dielectric constant (εr = 2.17) and dissipation factor available. The printed circuit board is glued to copper for dissipation purposes. Figure 5. Device footprint 5/13 Circuit schematic and bill of material Figure 6. 4 Cross section Circuit schematic and bill of material Figure 7. Broadband power amplifier Table 2. Bill of material Components 6/13 AN2048 Description B1, B2 Ferrite bead C1, C16 300 pF, 100 B ATC chip capacitor C2, C15 0.8 ÷ 8 pF var. cap. Gigatrim Johanson C3, C14 4 ÷ 25 pF var. cap. Murata TZBX4Z250AA110 C4 7 ÷ 50 pF var. cap. Murata TZBX4R500AA110 C5, C12 120 pF, chip capacitor Murata C6, C11 0.1 nF, chip capacitor Murata C8, C9 10 µF, 50 V electrolytic capacitor C7, C10 1 nF, CHIP capacitor Murata C13 6.5 30 pF var. cap. Murata TZBX4P300AA110 L 56 nH coilcraft R1 33 kΩ chip resistor 1/4 W R4 15 Ω melf resistor 1/4 W AN2048 Transmission line Table 2. Bill of material (continued) Components 5 Description R3 1 kΩ chip resistor 1/4 W J1, J2 SMA connector Board Arlon DiClad 880 THK 0.020‘‘ ε r= 2.17 2OZ ED Cu both sides Transmission line The microstrip layout (gerber files available on request) is shown below in Figure 8. Figure 8. 5.1 Transmission line Characterization results After tuning for the best performance the results are as shown in Figure 9. 7/13 Transmission line Figure 9. AN2048 Power gain vs. frequency Figure 10. Input return loss vs. frequency 8/13 AN2048 Transmission line Figure 11. Drain efficiency vs. frequency Figure 12. Drain efficiency vs. frequency at different drain voltages Figure 13. Power out vs. drain voltage at different frequencies 9/13 Transmission line AN2048 After the electrical analysis, the PD54008L-E was removed from the pcb and the input/output impedances were measured. Figure 14. Impedance data schematic Table 3. 10/13 Impedance data F(MHz) Z1 (Ω) Z2 (Ω) 450 1.0+j2.9 1.8+j0.5 460 0.9+j3.0 1.9+j0.7 470 0.9+j3.4 1.9+j0.9 AN2048 6 Components layout Components layout Figure 15. PCB layout Figure 16. PD54008L-E amplifier 11/13 Characterization results 7 AN2048 Characterization results As we can see from Figure 9, 10 and 11, we can achieve a minimum gain of 12 dB with an input return loss better than 5 dB and a drain efficiency between 55% and 65% over the frequency band 445 ÷ 475 MHz. Even so the output power can be controlled through Vgs, a minimum of 15 dB dynamic range can be achieved by varying Vdd (Figure 13). This allows better control of the transmitted power out and may extend the transmission range capability to more than 3 miles (depending on environment) as requested in some commercial products. 8 Feature characteristics Other optional functions in which this application may be used are: 9 10 ● Equipment monitoring ● CO/Methane/Fire detection ● Security/Alarm services ● Data logging ● All VHF and UHF PMR portables References 1. "RF power amplifiers for wireless communications", Artech House 2. "RF transistors meet wireless challenges" - Technical Editor - EDN magazine pag. 53 61, May 3, 2001 - www.ednmag.com. 3. "PowerSO-10RF - The first true RF power SMD Package" - Application Note 1294 STMicroelectronics. 4. "Understanding LDMOS device fundamentals" Application Note 1226 STMicroelectronics. Revision history Table 4. 12/13 Document revision history Date Revision Changes 14-Oct-2004 1 Initial release 06-Feb-2008 2 Document reformatted no content change PD54008L replaced by PD54008L-E AN2048 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. 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