Rf signal combiner/splitter and related methods

0001The present invention relates to the field of radio frequency combiner/splitter circuits, and, more particularly, to toroidal radio frequency combiner/splitter circuits and related methods.

0002Wireless communications devices are an integral part of society and permeate daily life. The typical wireless communications device includes an antenna, and a transceiver coupled to the antenna. The transceiver and the antenna cooperate to transmit and receive communications signals.

0003A typical radio frequency (RF) transceiver includes a power amplifier for amplifying low amplitude signals for transmission via the antenna. Given that most mobile communications devices operate on limited battery power, energy efficient power amplifiers may be desirable. More specifically and as will be appreciated by those skilled in the art, Class C and E power amplifiers are common in mobile communications devices since they are efficient power amplifiers. These classes of power amplifiers are more efficient than Class A or B amplifiers, for example, but are subject to performance tradeoffs. For example, they may be nonlinear over certain frequencies and may introduce greater amounts of distortion into the amplified signal (if the signal requires a linear amplifier).

0004In some communications applications, two or more smaller power amplifiers may be combined to provide a cumulative output without the incumbent complexity of a larger device. In other applications, a single amplifier may not be able to provide the needed performance in a practical implementation. This combination of two smaller amplifiers may be provided with a power RF combiner circuit. The "Wilkinson" type combiner is a typical RF combiner circuit with a number of input ports, for example, as disclosed in <patcit id="pcit0001" dnum="US3091743A"><text>U.S. Patent No. 3,091,743 to Wilkinson</text></patcit>. The "Wilkinson" type power combiner may obtain input port-to-port isolation for each port by feeding each of the other ports with the signal applied to any one port through resistors with a 180 degree phase shifted voltage, with one-quarter wavelength transmission lines providing the 180 degree phase shift required for cancellation. For high frequency (HF) applications, i.e. 2 to 30 MHz, the physical length of the one-quarter wavelength transmission lines becomes impractical for many applications.

0005An approach to this drawback of "Wilkinson" type power combiners in HF applications may include using ferrite transformers instead of the one-quarter wavelength transmission lines, for example, as disclosed in <patcit id="pcit0002" dnum="US3428920A"><text>U.S. Patent No. 3,428,920 to Oleksiak</text></patcit>. Referring to <figref idref="f0001 f0002">FIGS. 1-2</figref>, another such power combiner <b>20</b> is shown. This wound-wire type toroidal power combiner <b>20</b> illustratively includes a circuit board 23, a 100-Ohm bridging resistor <b>24</b> installed on the circuit board for dissipating any power mismatch in input power supplies <b>31-32</b> (50-Ohm input impendence), and three toroidal transformers <b>25a-25c</b> installed on the circuit board and defining a power combiner circuit. Each toroidal transformer <b>25a-25c</b> illustratively includes a ferrite core <b>22a-22c</b> and Teflon coated windings <b>21a-21c</b> surrounding the respective ferrite core. The wound-wire type power combiner <b>20</b> illustratively includes a 50-Ohm load resistor <b>27</b> coupled to the toroidal transformer <b>25c</b>.

0006As will be appreciated by those skilled in the art, the Teflon coated windings <b>21a-21c</b> are typically hand wound through the ferrite cores <b>22a-22c</b> and are used for their desirable high breakdown voltage properties. Moreover, Teflon coated windings may be costly. This makes the manufacturer of such HF power combiners time consuming and expensive.

0007<patcit id="pcit0003" dnum="US4201965A"><text>US 4,201,965</text></patcit> discloses a hi-Q inductor comprising a printed inductance. The printed inductance is obtained through four conductive traces structured as coils which are connected in series each other. The conductive coils are wound around sections of a ring-like electromagnetic core. The sections are inserted into opening 36 of the support of the printed inductance.

0008In view of the foregoing background, it is therefore an object of the present invention to provide a radio frequency (RF) combiner/splitter that is more effective and more easily manufactured.

0009This and other objects, features, and advantages in accordance with the present invention are provided by a printed circuit board (PCB) according to claim 1 and having first and second opposing major surfaces, and a plurality of openings therethrough. The RF signal combiner/splitter also includes a ferromagnetic body comprising a first portion spaced from the first major surface of the PCB, a second portion spaced from the second major surface of the PCB, and a plurality of interconnecting portions coupling the first and second portions and extending through respective openings in the PCB. The PCB includes conductive traces cooperating with the ferromagnetic body to define circuitry, for example, operable over a frequency range of 2 to 30 MHz, for combining/splitting RF signals. Advantageously, the toroidal RF signal combiner/splitter may be manufactured without cumbersome wire windings.

0010More specifically, the circuitry for combining/splitting RF signals comprises a plurality of summing toroidal inductors. The PCB may further comprise additional conductive traces cooperating with the ferromagnetic body to define impedance matching circuitry coupled to the circuitry for combining/splitting RF signals. Furthermore, the impedance matching circuitry may comprise a plurality of transformer toroidal inductors.

0011In some embodiments, the RF signal combiner/splitter may further comprise a plurality of RF signal ports coupled to the conductive traces. The ferromagnetic body may also comprise a plurality of joined together segments. Furthermore, the RF signal combiner/splitter may further comprise at least one load resistor coupled to the conductive traces. For example, the PCB may comprise at least one planar dielectric layer.

0012Another aspect is directed to a method of making a circuit board PCB to operate as a radio frequency (RF) signal combiner/splitter defined in claim 6. The method includes providing a printed circuit board (PCB) having first and second opposing major surfaces, and a plurality of openings therethrough. The method also includes positioning a ferromagnetic body comprising a first portion spaced from the first major surface of the PCB, a second portion spaced from the second major surface of the PCB, and a plurality of interconnecting portions coupling the first and second portions and extending through respective openings in the PCB. The PCB comprises conductive traces cooperating with the ferromagnetic body to define circuitry for combining/splitting RF signals. <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a perspective view of a toroidal signal combiner/splitter according to the prior art.</li><li><figref idref="f0002">FIG. 2</figref> is a schematic circuit diagram of the signal combiner/splitter of <figref idref="f0001">FIG. 1</figref>.</li><li><figref idref="f0003">FIG. 3</figref> is a side elevational view of a RF signal combiner/splitter according to the present invention.</li><li><figref idref="f0003">FIG. 4a</figref> is a cross-sectional view taken along lines 2-2 of the RF signal combiner/splitter of <figref idref="f0003">FIG. 3</figref>.</li><li><figref idref="f0004">FIG. 4b</figref> is a side view of the top portion of the ferromagnetic body of the signal combiner/splitter <figref idref="f0003">FIG. 3</figref>.</li><li><figref idref="f0005">FIG. 5</figref> is a plane topside view of the signal combiner/splitter of <figref idref="f0003">FIG. 3</figref> with the top portion of the ferromagnetic body removed.</li><li><figref idref="f0006">FIG. 6</figref> is a plane topside view of the RF signal combiner/splitter of <figref idref="f0003">FIG. 3</figref>.</li><li><figref idref="f0007">FIG. 7</figref> is a pseudo schematic cross-sectional view taken along lines 3-3 of the RF signal combiner/splitter of <figref idref="f0003">FIG. 3</figref>.</li><li><figref idref="f0008">FIG. 8</figref> is a schematic circuit diagram of the RF signal combiner/splitter of <figref idref="f0003">FIG. 3</figref>.</li><li><figref idref="f0008">FIG. 9</figref> is a chart of the electrical characteristics of the RF signal combiner/splitter in <figref idref="f0003">FIG. 3</figref>.</li></ul>

0013The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may; however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

0014Referring initially to <figref idref="f0003 f0004 f0005 f0006 f0007">FIGS. 3-7</figref>, a radio frequency (RF) signal combiner/splitter <b>40</b> is now described. As will be appreciated by those skilled in the art, the RF signal combiner/splitter <b>40</b> may be used as a combiner or a splitter depending on the direction of the signals. The RF signal combiner/splitter <b>40</b> illustratively includes a printed circuit board (PCB) <b>41</b>. The PCB <b>41</b> has first <b>49</b> and second <b>51</b> opposing major surfaces and may include at least one planar dielectric layer and/or a ground plane. The PCB <b>41</b> also illustratively includes a plurality of openings <b>55a-55e</b> therethrough. The openings <b>55a-55e</b> are illustratively rectangle-shaped, but may have other shapes, for example, circular or N-sided polygonal shapes.

0015The RF signal combiner/splitter <b>40</b> illustratively includes a ferromagnetic body <b>45</b> coupled through the PCB <b>41</b>. The ferromagnetic body <b>45</b> may comprise ferrite, for example, and illustratively includes a first portion <b>47</b> spaced from the first major surface <b>49</b> of the PCB <b>41</b> and a second portion <b>48</b> spaced from the second major surface <b>51</b> of the PCB. The ferromagnetic body <b>45</b> also illustratively includes a plurality of interconnecting portions <b>46a-46e</b> coupling the first <b>47</b> and second <b>48</b> portions and extending through respective openings <b>55a-55e</b> in the PCB <b>41</b>. Perhaps as best seen in <figref idref="f0004">FIGS. 4b</figref> and <figref idref="f0005">5</figref>, the ferromagnetic body <b>45</b> may also comprise a plurality of joined together segments <b>47-48.</b> In these embodiments, the first <b>47</b> and second <b>48</b> portions of the ferromagnetic body <b>45</b> may be joined together with ferrite adhesive, for example. In other embodiments, the ferromagnetic body may also comprise an integrally formed monolithic block, i.e. one piece.

0016As perhaps best seen in <figref idref="f0005">FIG. 5</figref>, the PCB <b>41</b> illustratively includes conductive traces <b>42-43</b> formed on the first major surface <b>49</b>. The conductive traces <b>42-43</b> may comprise copper or aluminum, for example. The conductive traces <b>42-43</b> cooperate with the ferromagnetic body <b>45</b> to define circuitry for combining/splitting RF signals. The RF signal combiner/splitter <b>40</b> illustratively includes a plurality of RF signal ports <b>44a-44b</b> coupled to the conductive traces <b>42-43</b>.

0017Referring briefly and additionally to <figref idref="f0008">FIG. 8</figref>, the circuitry of the RF signal combiner/splitter <b>40</b> illustratively includes a pair of radio frequency signal sources <b>54a-54b</b> (50-Ohm input impendence) coupled to the RF signal ports <b>44a-44b</b>, a 100-Ohm bridging resistor <b>70</b> coupled therebetween and for dissipating any power differential in the radio frequency signal sources, and a first set <b>52</b> of summing (combiner) toroidal inductors, i.e. coupled toroidal inductors, (2-three turn inductors), formed from the conductive traces and the ferromagnetic body, for combining the input power supplies. The circuitry of the RF signal combiner/splitter <b>40</b> also illustratively includes a second set <b>53</b> of transformer toroidal inductors (1-two turn inductor and 1-four turn inductor, i.e. 4T:6T auto transformer 1:2.25 Z(impedance)-ratio) for providing a step-up impedance transformer, and a 56.25 load impedance <b>73</b> also coupled to the conductive traces <b>42-43.</b> As will be appreciated by those skilled in the art, the ideal load impedance would a 50-Ohm load; nonetheless, the illustrated embodiment includes a near ideal 56.25-Ohm load impedance <b>73.</b>

0018The RF signal combiner/splitter <b>40</b> illustratively includes a center tap wire <b>58</b> coupling the first set <b>52</b> of summing toroidal inductors to the second set <b>53</b> of transformer toroidal inductors. In other embodiments, the center tap wire <b>58</b> may alternatively be formed on the first major surface <b>49</b> of the PCB <b>41</b> as a conductive trace.

0019As will be appreciated by those skilled in the art, this 56.25-Ohm output impedance <b>51</b> is provided by the second set <b>53</b> of transformer toroidal inductors, i.e. a 36/16 conversion ratio (25-Ohm * 36/16 =56.25-Ohm). More particularly, at point <b>71</b>, the impedance of the circuit is 25-Ohm. The circuitry of the RF signal combiner/splitter <b>40</b> is operable over a frequency range of, for example, 2 to 30 MHz for combining/splitting RF signals, i.e. high frequency signals.

0020Referring additionally to <figref idref="f0008">FIG. 9</figref>, a chart <b>60</b> illustrates the electrical performance of the RF signal combiner/splitter <b>40</b>. More particularly, the left-side y-axis represents port loss in decibels and the x-axis represents frequency in MHz. The right-side y-axis represents port return loss in decibels. In this test result, the RF signal combiner/splitter <b>40</b> is operated as a splitter, i.e. a single power source is fed into the output of the second set <b>53</b> of transformer toroidal inductors and two split signals are provided at the RF signal ports <b>44a-44b.</b> As will be appreciated by those skilled in the art, the ideal splitter would receive input signal x(t) and output two split signals equaling 0.5*x(t), i.e. a power reduction of 3 decibels. Curves <b>61-62</b> demonstrate the near ideal performance (approximately -3 decibels) of the RF signal combiner/splitter <b>40</b> in the HF range, i.e. 2-30 MHz. Curves <b>63-64</b> demonstrate the near ideal return loss performance of the RF signal combiner/splitter <b>40</b> in the HF range, i.e. 2-30 MHz.

0021Advantageously, the above described RF signal combiner/splitter <b>40</b> is toroidal and well suited for HF applications yet may be manufactured without cumbersome hand wound wire coils. In other words, the RF signal combiner/splitter <b>40</b> may be manufactured without intensive manual labor. Indeed, the RF signal combiner/splitter <b>40</b> uses no soldering for assembly and may be manufactured before any wave soldering is used. Helpfully, the RF signal combiner/splitter <b>40</b> uses no external assemblies and is more mechanically robust than the typical wound-wire type power combiner. Moreover, the RF signal combiner/splitter <b>40</b> is readily manufactured with repeatable and consistent performance since the manual manufacture component of the typical power combiner is removed. Also, since the RF signal combiner/splitter <b>40</b> does not use expensive Teflon coated windings, the cost of manufacture is reduced.

0022Another aspect is directed to a method of making a circuit board PCB to operate as a RF signal combiner/splitter <b>40.</b> The method includes providing a PCB <b>41</b> having first <b>49</b> and second <b>51</b> opposing major surfaces, and a plurality of openings <b>55a-55e</b> therethrough. The method also includes positioning a ferromagnetic body <b>45</b> comprising a first portion <b>47</b> spaced from the first major surface <b>49</b> of the PCB <b>41,</b> a second portion <b>48</b> spaced from the second major surface <b>51</b> of the PCB, and a plurality of interconnecting portions <b>46a-46e</b> coupling the first and second portions and extending through respective openings <b>55a-55e</b> in the PCB. The PCB <b>41</b> comprises conductive traces <b>42-43</b> cooperating with the ferromagnetic body <b>45</b> to define circuitry for combining/splitting RF signals.