Mobile Communications LTE PAs Offer Fast, Powerful Wireless Data Options� C onsumers are demanding more from their mobile devices, including increased bandwidth. They have become accustomed to the near universal data connectivity of smartphones and tablets including applications that continually demand higher and higher data rates. Given the variety of LTE frequency bands, and the range of preferred power levels, RFMD has developed a family of LTE-compatible power amplifiers for data connectivity applications. They are summarized in Table 1. TABLE I RFMDs family of power amplifiers for LTE dAta connectivity Part Number Frequency Range (GHz) Integration Linear Power (dBm) Supply Voltage (V) Current (mA) RF5602 2.3 to 2.7 Unmatched PA 21 to 23 3.3 to 5 350 to 450 RF5603 3.3 to 3.8 Unmatched PA 23 3.3 425 RF5607 1.9 to 2.7 Unmatched PA 22 5 350 RF5612 2.5 to 2.7 Matched PA 22 3.3 470 RF5623 3.3 to 3.8 Unmatched PA 24 5 600 RF5652 2.3 to 2.7 Unmatched PA 28 5 1200 RFFM7600 2.3 to 2.7 Matched PA+SPDT 24 5 650 32 As can be seen, a wide range of LTE bands can be covered by these PAs. The RF5607, for example, has a large frequency coverage capability of 1.9 to 2.7 GHz. This allows the customer to tune to a desired frequency band within this range. The RF5602 is similar and offers higher output power with less frequency coverage. It can also be efficiently operated at lower power with a reduced Vcc. The linear power listed for each of these amplifiers is for a nominal linearity requirement, and varies depending on the specific modulation used. The RF5612 is intended for uplink applications, the others are primarily intended for the downlink. Many of the amplifiers in Table 1 can also be used in WiMAX applications, typically at higher output powers. RFMD continues to add to its LTE power amplifier family, with higher power levels in particular, soon to be available. RF5607 The RF5607 is a versatile member of RFMD’s LTE power amplifier family. It is RF Micro Devices Greensboro, NC MOBILE COMMUNICATIONS n NOVEMBER 2011 Mobile Communications VCC1 N/C VCC2 VCC2 16 15 14 13 BIAS VCC 1 12 RF OUT 1st STAGE 3rd STAGE 2nd STAGE INTERSTAGE MATCH INTERSTAGE MATCH RF IN 2 10 RF OUT VREG2 6 7 8 VREG3 N/C PDETECT L6 3.9 nH 1 12 2 11 3 10 4 9 5 6 7 C9 5.6 pF 8 Block diagram of the RF5607. R3 56 C7 330 pF C2 1000 pF PDOWN s Fig. 3 VREG2 PDET Schematic of the RF5607 in a 2.1 to 2.2 GHz application. G (dB) ACP (dBc) ure 4. As shown, ACLR remains –25 well below the -44 –30 –35 dBc requirement –40 up to 22 dBm out–45 put power. At that –50 point, nonlineari–55 ties resulting from –60 –65 the large peak to 0 5 10 15 20 25 30 average power raPO (dBm) tio (PAPR) of the modulated sig- s Fig. 4 Typical linearity performance of the nal begin to de- RF5607 with a 10 MHz modulated LTE signal grade ACLR. The at frequencies between 2.11 and 2.17 GHz. RF5607 actually 40 0.50 provides -45 dBc 35 0.45 ACLR. 30 0.40 Gain and cur25 0.35 20 0.30 rent consumption 15 0.25 are also impor10 0.20 tant power ampli5 0.15 fier characteristics. 0 0.10 5 10 15 20 25 They are shown PO (dBm) versus output power in Figure Fig. 5 Typical gain and current consump5. Note how gain s tion performance of the RF5607 with a 10 is only lightly com- MHz modulated LTE signal at frequencies pressed even at between 2.11 and 2.17 GHz. the full LTE rated power of 22 dBm. This highlights the very linear operation that LTE downlinks demand. The current consumption is below 330 mA, even at 22 dBm. Current increases gradually from about 230 mA at quiescence. Since the output stage operates in deep Class AB, the low impedance active bias ICC (A) designed using RFMD’s InGaP HBT process. The block diagram, Figure 1, shows that this is a threestage power amplifier with integrated power detection and active bias s Fig. 2 The RF5607 LTE downlink PA ap- control. All stages plication board for 2.1 to 2.2 GHz operation. use a 3 × 20 µm dual emitter HBT unit cell. Two cells are used in the first stage. The second and third stages are scaled up to 8 and 32 cells, respectively. The PA operates in Class AB mode. The second harmonic termination at the output is implemented with an on-chip capacitor and an in-package down bond. The first and second stages are each biased with a two-diode emitter follower. RFMD’s proprietary active bias circuit supplies bias to the final stage while providing low impedance for linear operation over the operating range. A unique feature of the RF5607 is that the input and output matching networks are off chip. Interstage matching is broadband to cover the entire 1.9 to 2.7 GHz frequency range. Actual applications are in much narrower bands within this range. Ultimate performance is critically dependent on output match and to a lesser extent on input match. Therefore, optimized matching for specific LTE downlink bands has been developed for implementation off-chip. Figure 2 shows an application board for 2.1 to 2.2 GHz operation. The application boards for other bands are identical, only the values of the matching components change. The schematic, with matching components optimized for a 2.1 to 2.2 GHz LTE downlink is shown in Figure 3. The RF5607 uses a 3 × 3 mm QFN package. ESD protection is included on all pins to both Human Body Model (HBM) and Charged Device Model (CDM) requirements. The exact band of operation is tunable with external components. The key performance attributes for an LTE power amplifier are power, ACLR and current consumption. Typical power and linearity for the RF5607 are shown in Fig 16 15 14 13 C8 3.3 pF 5 L5 3.9 nH C16 1 uF C19 3.3 pF 9 N/C VREG1 4 J1 RF IN R1 15 C3 1 pF L3 12 nH J2 RF OUT DETECTOR BIAS 34 C1 1000 pF C11 1 uF R4 100 C13 330 pF 11 RF OUT PDOWN 3 s Fig. 1 VCC (Continued on page 38) MOBILE COMMUNICATIONS n NOVEMBER 2011 Mobile Communications Intermod Squad: Low PIM Connectors D ubbed the Intermod Squad, Santron has developed a new series of low PIM cable assemblies that feature intermodulation performance as low as -181 dBc with an eSeries 7/16 connector terminated on TFlex-402 cable. Typical performance across the lineup of assemblies terminated with eSMA and eSeries Type N’s is -162 dBc. The eSMA cable assemblies perform from DC to 20 GHz and the eSeries Type N cable assemblies perform from DC to 18 GHz. These assemblies are phase and attenuation stable, provide excellent shielding, support UL/NEC Plenum class CMP, are corrosion resistant, and are low in weight and highly flexible. The key component in San-tron low PIM cable assemblies are the latest series of connectors. eSeries connectors, which include SMA (trademarked as eSMA), Type N, TNC and 7/16 styles, offer evolved cable/connector transitions. The repeatability of these transitions from the cable into the connector is key to the consistent high performance of these cable assemblies. The center contact is a solder-free connection so the transition is controlled to machined tolerances, which are much tighter than the variations seen by cable assembly personnel and solder joints. Another advantage of the elimination of this center conductor solder joint is it precludes the changes that occur in dielectric densities that would affect changes in the dielectric constant. Also, the connector bodies contain an internal stop to locate the cable position into the connector. Reliability is improved with these connectors with an extended ferrule that is crimped onto the body that provides longitudinal protection out past this wick line, which is a traditional fail- ure point. For added protection, dual wall heat shrink is positioned within the saddle of this crimp ferrule and further extends the strain relief from this wick line offering high reliability in applications that involve repeated flexure. The Albaloy plating provides a robust surface that easily accepts the braid solder joint and supports corrosion resistance per salt fog testing. The eSMA center contacts are BeCu; they are plated gold over a copper strike providing excellent RF performance, corrosion resistance and control over porosity. The eSeries N and 7/16 center contacts are plated silver over a copper strike, which contains cost versus gold, and also provides good RF performance and corrosion resistance. San-tron Inc., Ipswich, MA (978) 356-1585, www.santron.com. ACP (dBc) (Continued from page 34) –25 –30 –35 –40 –45 –50 –55 –60 –65 0 5 10 15 20 PO (dBm) 25 30 s Fig. 6 Typical linearity performance of the RF5607 with a 10 MHz modulated LTE signal (blue) and a 5 MHz W-CDMA modulated signal (black) at frequencies between 2.11 and 2.17 GHz. network allows current to increase so that linearity is maintained as drive level grows. Figure 6 shows the power and linearity performance of the RF5607 with both a LTE downlink signal and a W-CDMA signal. LTE has a wider modulated bandwidth and a higher 38 data rate than W-CDMA. This increases the linearity demands on the system and on the PA. As Figure 6 shows, this can be directly seen in power amplifier performance. Linearity is 1.5 to 2.5 dB better with the W-CDMA signal. LTE provides users with very high data rates in mobile devices enabling streaming multimedia and supporting the growth of social networking and the push to cloud computing. LTE imposes unique system requirements and presents challenges to the power amplifier designer, particularly of the downlink. RFMD has developed a family of products to address these needs. They cover the key downlink frequency bands, provide an ACLR of better than -44 dBc and provide efficient operation with LTE modulation bandwidths of up to 20 MHz. RF Micro Devices, Greensboro, NC (336) 664-1233, www.rfmd.com. MOBILE COMMUNICATIONS n NOVEMBER 2011