® TECHNICAL SECTION INSERTION LOSS (S-2) AMPLITUDE UNBALANCE 4.4 0.7 avg (dB) avg - 4.5 sig avg + 4.5 sig avg (dB) AMPLITUDE UNBALANCE (dB) Figure 1 The SBTC power splitter/combiners make use of a highly integrated manufacturing approach to achieve broad bandwidths in a tiny package. INSERTION LOSS(dB) 4.2 4.0 3.8 3.6 3.4 3.2 10 100 FREQUENCY (MHz) Fig. 3 1000 10000 Figure 3 The "lot" insertion loss performance of one of the SBTC-2-10’s output ports is shown in terms of statistical parameters. These tiny power splitters use LTCC technology to deliver full-sized performance for signal processing applications where PCB area is at a premium. P ower splitters/combiners are the invaluable passive components that allow transmitters and receivers to add and subtract signals as necessary. Traditionally, broadband power splitters/combiners operating below 2.5GHz have been based on ferrite transformers in order to convert an internal point of low input impedance to the 50 ohm characteristic impedance of an RF system. Due to the inclusion of the transformer, broadband splitters have required relatively large package sizes. But the SBTC model power splitters from Mini-Circuits provide a breakthrough by squeezing full-scale, broadband performance into a compact package measuring only 0.15" (0.38cm) on a side including height. These SBTC models (Figure 1) are 2-way power splitters that also serve as power combiners. They compare in performance to currently available multi-decade-bandwidth splitters from Mini-Circuits measuring 0.25"x0.31" (0.64x0.79 cm) and larger. Reductions in size of power splitters has been possible by using external resistors and capacitors1, but at a sacrifice in parts count and lost printed-circuit-board (PCB) space due to the use of the external components. The SBTC models require no external components, making use of high-level integration techniques to pack all necessary components within a tiny surface mount package. Since the SBTC splitters are so small, multiple output splitters (such as 4-way and 8-way) can be formed by cascading several units while saving valuable PCB space. Basically, a power splitter is formed of an input impedance-matching section, a divider section, a capacitor, and a resistor. In a 50 ohm system, the impedance at the input of the divider is close to 25 ohms. The matching transformer converts this low input impedance to the characteristic 50 ohm of most RF systems at the RF input to provide good impedance match for minimal signal power loss. Normally, a capacitor (C) is required to match the reactive part of the impedance. The resistor (R) plays a critical role in providing isolation between the two RF output ports. Figure 2 shows the relationship of these four components. avg + 4.5 sig 0.5 0.4 0.3 0.2 0.1 0.0 3.0 1 TINIEST 2-WAY SPLITTERS CHANNEL SIGNALS WITHIN 5 TO 2500MHz avg - 4.5 sig 0.6 As mentioned before, traditional construction of a splitter requires a large PCB area. In contrast, size reduction is achieved in the SBTC units by constructing the base with Blue CellTM technology, which is based on low temperature cofired ceramic (LTCC) fabrication techniques. The LTCC technology is mature; it is also employed in the fabrication of active multichip modules (MCMs) for applications such as cellular base stations and Bluetooth transceiver modules. In the power splitter, the Blue CellTM technology makes it possible to embed the resistor and the capacitor within the splitter circuitry, while a ferrite transformer is used to perform both the power splitting and matching functions. Connections RF Input between components and to the package are formed through the company’s proprietary welding process. Electrical contacts are brought to the bottom of the splitter circuit board through via-hole connections. The result is power splitter/combiners capable of broad-bandwidth operation within 5 to 2500MHz with low insertion loss, high isolation, and very repeatable performance from unit to unit. Power splitter performance can be specified in terms of several key parameters such as insertion loss, isolation, power handling capability, amplitude imbalance, phase imbalance, and voltage standing-wave ratio (VSWR). In a power splitter, the measure of insertion loss is the difference between the amplitude of the input signal and each output signal, but also taking into account the theoretical loss associated with splitting a signal. In a two-way power splitter, for example, each output signal is ideally 3dB less in amplitude than the input signal. In a four-way splitter, the power splitting difference is 6dB. 1 10 100 FREQUENCY (MHz) 1000 10000 Fig. 4 Figure 4 The measured amplitude unbalance is considerably less than the specified maximum value of 0.6dB from 0.5 to 1000MHz. So, specifications presented for power splitter insertion loss generally assume the splitting loss, showing only the insertion loss above whatever signal losses occur due to power division. Isolation in a power splitter is a measure of the signal cross talk that occurs between ports or channels. It is defined as the attenuation between a signal at any output port and the level of the signal at another output port, with the input port terminated in 50 ohms. Unwanted signal RF Output 1 MATCHING TRANSFORMER DIVIDER R C RF Output 2 Figure 2 The SBTC-2-10 consists of four basic components; an input impedance matching section, a divider section, a capacitor, and a resistor. All are integrated within the package. feedthrough or cross talk can result in undesirable spurious signal products further along the signal-processing chain in a system. The highest values of isolation are preferred, with values of 20dB or better generally acceptable for most applications. The power-handling capability of a splitter/combiner depends upon the use of the component. As a divider, the component can handle higher input power levels than as a combiner, where the resulting output power level will be some combination of the total input-power levels minus the insertion loss. Since a splitter/combiner must dissipate continued on 26 ® P.O. Box 350166, Brooklyn, New York 11235-0003 (718) 934-4500 Fax (718) 332-4661 For quick access to product information see MINI-CIRCUITS CATALOG & WEB SITE TM The Design Engineers Search Engine Provides ACTUAL Data Instantly From MINI-CIRCUITS At: www.minicircuits.com 24 ISO 9001 ISO 14001 CERTIFIED see us on the web www.minicircuits.com 25 ® TECHNICAL SECTION TINIEST 2-WAY SPLITTERS CHANNEL SIGNALS WITHIN 5 TO 2500MHz continued from 25 at RF level -10 dBm 35 31 ISOLATION (dB) 3.0 2.5 2.0 1.5 27 S-2 4.0 INSERTION LOSS (dB) avg + 4.5 sig 3.5 4.2 4.0 3.8 3.6 3.4 23 3.8 3.6 3.4 3.2 3.2 S-1 1.0 3.0 19 0.5 avg (dB) avg - 4.5 sig S-2 3.0 50 150 250 350 avg + 4.5 sig 450 550 650 750 850 950 1050 0 100 200 300 FREQUENCY (M H z) 400 500 600 700 800 900 1000 FREQUENCY (M H z) 15 0.0 1000 10000 1 10 100 1000 10000 at RF level -10 dBm Fig. 6 power as heat internally, the input-power specification for the combiner function is lower compared to the specification for use as a power splitter. Component repeatability is of prime concern for system designers. The compact nature of the SBTC design results in very repeatable performance. For example, Figure 3 shows the insertion loss performance of the SBTC-2-10 through three curves. One curve identifies the mean performance of multiple units, while the two other curves show the mean minus 4.5 sigma value and the mean plus 4.5 sigma value. The insertion loss above the nominal 3dB splitting loss is rated as typically 0.3dB at lower frequencies and in midband, and typically 0.5dB at the upper frequencies. The maximum insertion loss across the operating band is 1.4dB. The compact design of the SBTC-2-10 results in a very small standard deviation (typically 0.02dB), indicating that variations from unit to unit are almost negligible. The manufacture of the unit provides very consistent insertion loss between individual ports. Figure 4 shows the amplitude imbalance-the difference in amplitude between the splitter’s two output ports. The amplitude imbalance is rated at a maximum of 0.6dB across the full operating band. Measurements indicate typical amplitude imbalance of only 0.1dB, with a standard deviation of 0.04dB. The phase imbalance is similarly impressive. Rated at a maximum of 5 degrees across the full operating band, and as low as 3 degrees from midband to the lowerfrequency limit, measurements show the phase imbalance to be considerably less than the specified level (Figure 5), with variations between units being extremely small (a standard deviation of typically 0.1 degree). The SBTC-2-10 is rated at isolation of typically 29dB at the lower frequencies, 25dB at midband, and typically 21dB at the upper-frequency limit, with worst-case isolation of 16dB across the full operating band. Actual measurements show the isolation between ports to be typically 20dB through 1000MHz (Figure 6). This parameter is normally very sensitive to assembly parasitics in other designs and varies from unit to unit. In the SBTC-2-10, the standard deviation for isolation is typically 0.5dB, which signifies very low unit-to-unit variation. The input/output matching of the power splitter is well controlled, with VSWR performance typically 1.15:1. The SBTC family contains 7 patent pending 2-way 0° splitters including two 75 ohm and two impedance matching models. The SBTC-2-10-5075 impedance matching splitter is for converting 50 ohm input to 75 ohm output in the 50 to 1000MHz band, and the SBTC-2-10-7550 is for 75 ohm input to 50 ohm output within 5 to 1000MHz. Performance curves for these models are shown in Figure 7. All SBTC splitter/ combiners are capable of handling input power levels as high as 0.5W (as splitter) with the SBTC-2-25 capable of handling up to 1W. SBTC power splitter/combiners are available in tape-and-reel packaging for use on high volume, automated assembly production lines. They are rated for operating temperatures ranging from -40°C to +85°C and are available for immediate shipment. Detailed electrical performance for each model plus outline drawings and dimensions are available in this handbook, on the internet at http://www.minicircuits.com/psc1.html, or by contacting Mini-Circuits. 1. Engineering Staff, Mini-Circuits, "Do-It-Yourself Low-Cost Power Splitter", Microwave Product Digest, May 2000. at RF level -10 (dBm) 1.50 Figure 6 Measurements show the isolation between ports to be typically 20dB through 1000MHz. Figure 5 The measured phase imbalance compares well with the specified performance. SBTC-2-10-7550 VSWR SBTC-2-10-5075 VSWR FREQUENCY (MHz) Fig. 5 1.50 #S-VSWR 1.45 #1-VSWR #2-VSWR 1.45 1.40 1.40 1.35 1.35 1.30 1.30 VSWR 100 FREQUENCY (MHz) 1.25 1.25 1.20 1.20 1.15 1.15 1.10 1.10 1.05 1.05 1.00 #S-VSWR 150 250 350 450 550 650 750 850 950 1050 0 100 200 300 FREQUENCY (MHz) #2-VSWR 400 500 600 700 800 900 1000 FREQUENCY (MHz) SBTC-2-10-7550 ISOLATION SBTC-2-10-5075 ISOLATION 30 #1-VSWR 1.00 50 at RF level -10 dBm 34 at RF level -10 (dBm) 32 28 30 26 ISOLATION (dB) 10 VSWR 1 ISOLATION (dB) PHASE UNBALANCE (deg.) INSERTION LOSS (dB) avg - 4.5 sig S-1 4.4 4.0 avg (dB) at RF level -10 (dBm) 4.2 4.6 ISOLATION (1-2) PHASE UNBALANCE SBTC-2-10-7550 INSERTION LOSS SBTC-2-10-5075 INSERTION LOSS 24 22 28 26 24 20 22 20 18 50 150 250 350 450 550 650 750 850 950 1050 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (M H z) FREQUENCY (M H z) Figure 7 Performance curves for SBTC impedance matching splitters. ELECTRICAL SPECIFICATIONS Model Freq. Isol. (MHz) Typ. (dB) SBTC-2-10 SBTC-2-20 SBTC-2-25 SBTC-2-10-75 SBTC-2-15-75 SBTC-2-10-5075 SBTC-2-10-7550 5-1000 200-2000 1000-2500 10-1000 500-1500 50-1000 5-1000 25 20 20 28 28 20 24 Ins. Loss* Typ. (dB) Phase Unbal. (Deg) (Max) Ampl. Unbal. (dB) (Max) Price $ea. Qty. 25 0.5 0.8 1.4 0.7 0.8 1.0 0.6 5 10 14 5 5 5 5 0.5 0.8 1.2 0.7 0.9 0.6 0.6 2.49 3.49 3.49 2.99 2.99 2.99 2.99 * Above 3.0dB ® P.O. Box 350166, Brooklyn, New York 11235-0003 (718) 934-4500 Fax (718) 332-4661 For quick access to product information see MINI-CIRCUITS CATALOG & WEB SITE TM The Design Engineers Search Engine Provides ACTUAL Data Instantly From MINI-CIRCUITS At: www.minicircuits.com 26 ISO 9001 ISO 14001 CERTIFIED see us on the web www.minicircuits.com 27