Highly Integrated and Compact Multichip Modules for Defense Applications
by Rick Montgomery, senior product line director, Qorvo & Dean White, director of product solutions, Defense and Aerospace, Qorvo & Jon Alejandro, customer account manager, High Performance Solutions, Qorvo
Highly Integrated RF Modules from Smarphones to Defense
Qorvo is known as a leader in providing highly integrated RF front end modules (FEMs) at multiple bands for cellular handset applications. Qorvo’s RF Fusion™ LTE portfolio contains multiple high-performance modules that deliver global carrier aggregation band coverage in the industry’s smallest form factors for today’s smartphones. Figure 1 shows a block diagram of RF Fusion modules used in an aggressive carrier aggregation environment with multiple inputs and multiple outputs (MIMO).
Each of the modules represented in Figure 1 has various integrated circuits constructed using processes such as HBT GaAs power amplifiers (PAs), SOI switches and BAW (bulk acoustic wave) filters. The modules are constructed on specialized laminates and over-molded to yield the smallest form factors possible.
Qorvo is now providing this same level of integration for systems integrators in defense markets, combining multiple integrated circuits and discrete parts on specialized laminates to reduce size and design complexity. Defense applications that are benefiting from higher levels of integration include FEMs for AESA (active, electrically scanned array) radar, multiple band radar drivers, and compact duplexer and amplifier combinations for communications and positioning. These defense modules are manufactured using the full spectrum of processes available at Qorvo, including GaN-on-SiC power transistors, pHEMT GaAs, low noise MMICs, BAW filters, GaAs HBT amplifiers, GaN and SOI switches, and CMOS controllers.
The modules are constructed using the same kinds of specialized laminates that Qorvo uses for cellular handset applications. These laminates include embedded heat spreaders for superior thermal conductivity and even lower cost lead frame construction. The modules may be over-molded or have cavity lids, depending upon performance and environmental constraints. In either case, these products allow Qorvo’s customers to reduce the amount of real estate required to implement a certain function by at least an order of magnitude.
FEMS for AESA Radar
New AESA radar designs often include digital or analog beamforming, accomplished using highly integrated CMOS or SiGe (silicon germanium). These modern systems still need compound semiconductors on the front end to achieve transmit power levels and receiver noise figures that are necessary to meet system requirements.
FEMs from Qorvo meet the system need for a compact, highly efficient PA on the transmit side and a low noise power limiting amplifier on the receive side. These modules are designed to interface directly with silicon or SiGe chips on one side, and with the antenna or duplexing element on the other. These FEMs eliminate the need for extensive front-end microwave design and test with a tested integrated solution for both transmit and receive paths.
Figure 2 shows a block diagram of an X-band FEM with an integrated switch. This FEM was designed to fit in a 5mm X 5mm over-molded QFN package. There is a reduction in gain and efficiency using over-mold when compared to an air-cavity lid, but this is offset by increased mechanical ruggedness and lower cost. This integrated FEM is fabricated using Qorvo’s 0.25um GaN technology which delivers maximum efficiency and minimizes the requirement for heat conduction away from the package and prime power. This module delivers 3 watts of pulsed power with an efficiency objective of greater than 32% over an 8.5 to 10.5 GHz bandwidth. The low noise amplifier is fabricated on the same MMIC as the PA and delivers less than 2.2 dB noise figure, including the losses from the package and the TR switch in front of the LNA.
This type of compact FEM makes it possible for system designers to meet their front-end performance requirements in a space which is limited by fixed element-to-element spacing and the high efficiency of the GaN MMIC amplifier makes it possible to deliver moderate power without excessive channel temperature in an environment where there are many amplifiers sharing the same limited thermal paths. Figure 3 shows the 5 mm x 5 mm over-molded package of the QPM1002.
Radar Power Modules for Multiple Bands
Multiple stages of discrete transistors can be integrated together to give large amounts of gain and power at specific radar bands. Qorvo is currently developing two of these modules. The QPA2511 is at L-band covering from 1.2 to 1.4 GHz and the QPA2513 covers S-band from 3.1 to 3.5 GHz. Block diagrams of both parts are shown in Figure 4. Both parts include two stages of gain and are matched to 50 ohms at input and output. These products will utilize laminates with embedded heat spreaders and an air-cavity for best performance. The input, output and inter-stage matching are accomplished on the laminate itself. Passive GaAs material is used for one of the matching lumped elements. The amplifier stages in this example are Qorvo GaN transistors and the total power available is 120 watts at either L or S-band. The power gain (P3dB) for either module is around 27 dB and the efficiency is estimated at a minimum of 62%. Figure 5 shows the power output and efficiency for the QPA2511.
The QPA2511 and QPA2513 are packaged in a 25 mm X 12.5 mm module which saves real estate and cost for the system integrator.
Diplexers and Band Splitters
Using Qorvo’s SAW technology and GaAs amplifiers, highly selective diplexers can be implemented in a very compact form factor with close frequency spacing, superior rejection and translational gain. The block diagram in Figure 6 provides an example.
This module delivers from 50 dB to 70 dB of out of band attenuation at frequencies offset by more than 100 MHz from the center frequency and 18 dB of small signal gain in each band. The noise figure in a 30 MHz wide passband is typically 3 dB. Qorvo can accomplish this in an extremely small 3.5 mm X 3.5 mm form factor shown in Figure 7.
Defense system integrators are beginning to take advantage of higher levels of integration. Devices can be fabricated as laminate and leadframe modules using integrated circuits with technologies such as GaN, GaAs and SAW. Integrated parts utilizing laminates or leadframe can be quick turnaround and utilize existing discreet and MMIC designs. High power, low noise and high frequency selective functions can be integrated together. Low thermal resistance for high power devices is accomplished using embedded heat spreaders for laminate modules and metal paddles for leadframe. Qorvo is working with several system integrators to design and supply highly integrated modules for various applications that reduce the real estate required for a particular function, lowering costs and simplifying design at the system level.