A multiplexer circuit may include a first-frequency-quarter-wavelength transmission line extending between a junction between a common terminal and a second-frequency terminal, and a first-frequency low-impedance circuit electrically directly connecting the first transmission line to a circuit ground. In some examples, a second-frequency-quarter-wavelength transmission line may extend between the first transmission line and a third-frequency terminal. A second-frequency low-impedance circuit may electrically directly connect the second transmission line to the circuit ground. The first and second transmission lines and the first and second low-impedance circuits may provide a third-frequency transmission line. A further second-frequency low-impedance circuit may electrically couple the second terminal to the first transmission line. A third-frequency low-impedance circuit may electrically couple the second terminal to the circuit ground. The first-frequency, further second-frequency, and third-frequency low-impedance circuits and the first transmission line may provide in combination a second-frequency transmission line.

BACKGROUND

As used in telecommunications, a frequency multiplexer (hereafter referred to simply as “multiplexer”) is a network that separates signals from or to a common port to or from other ports, sorted according to their frequency. Frequency sorting is conventionally achieved by a filter in each signal line between the common port and another port, which filter allows the signal for the associated signal line to pass while attenuating the other signals. The filters generally may be low-pass, band-pass, or high-pass filters as appropriate.

Multiplexers may be used in a mixer for up-converting or down-converting signals in a radio-frequency transmitter or receiver. In such an application, the multiplexer may be a triplexer. Generally, a mixer performs frequency conversion by multiplying two signals. For example, in a receiver, a radio-frequency signal and a local-oscillator signal may be multiplied to produce an intermediate-frequency or baseband signal. (Baseband signals, for which there may be no lower frequency limit, will be considered intermediate-frequency signals for the purpose of this discussion.) Similarly, in a transmitter, an intermediate-frequency signal and a local-oscillator signal may be multiplied to produce a radio-frequency signal.

Isolation between the various signal lines is important. Conventionally, a low-pass filter may be used in the intermediate-frequency signal line to allow substantially only the intermediate-frequency signal to be conducted. A band-pass filter may be used in the local-oscillator signal line to attenuate intermediate- and radio-frequency signals. A band-pass or high pass filter may be used in the radio-frequency signal line to attenuate intermediate- and local-oscillator signals. Additionally, the signal path to a common terminal desirably has low impedance for the signals in each of the signal lines.

BRIEF SUMMARY

In some examples, a multiplexer circuit may include a common terminal for conducting a signal having a first frequency and a signal having a second frequency different from the first frequency, a first terminal for conducting the signal having the first frequency, and a second terminal for conducting a signal having the second frequency. The first terminal may be electrically coupled to the common terminal, and the second terminal may be electrically coupled to the second terminal. In some examples, a multiplexer may include a first transmission line having a first end coupled to the first terminal and a second end coupled to the second terminal, and a first low-impedance circuit electrically directly connecting the second end of the first transmission line to a circuit ground. The first transmission line may have an electrical length substantially equal to a quarter wavelength of the first frequency and a first characteristic impedance at the first frequency. The first low-impedance circuit may provide at the first frequency an impedance that is less than half of the first characteristic impedance. The series combination of the first transmission line and the first low-impedance circuit may provide at the first frequency a first high impedance to ground at the first end of the first transmission line.

In some examples, a second transmission line may have a first end coupled to the common terminal and a second end coupled to the first terminal, the second transmission line having an electrical length substantially equal to a quarter wavelength of the second frequency, and a second low-impedance circuit may electrically directly connect the second end of the second transmission line to the circuit ground wherein the second low-impedance circuit provides at the second frequency a second low impedance. The series combination of the second transmission line and the second low-impedance circuit may provide at the second frequency a second high impedance to ground at the first end of the second transmission line.

In some examples, a multiplexer circuit may include a third terminal for conducting a signal having a third frequency different from the first and second frequencies. A second transmission line may have a first end coupled to the second end of the first transmission line and a second end coupled to the third terminal, with the second transmission line having an electrical length substantially equal to a quarter wavelength of the second frequency. A second low-impedance circuit may electrically directly connect the second end of the second transmission line to the circuit ground, wherein the second low-impedance circuit provides at the second frequency a second low impedance. In such examples, the series combination of the second transmission line and the second low-impedance circuit may provide at the second frequency a second high impedance to ground at the first end of the second transmission line.

In some examples, a further low-impedance circuit may electrically couple the second terminal to the second end of the first transmission line wherein the further low-impedance circuit provides at the second frequency a second low impedance. In some examples, a yet further low-impedance circuit may electrically couple the second terminal to the circuit ground wherein the yet further low-impedance circuit provides at the third frequency a low impedance.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

This description is illustrative and directed to examples of apparatus and/or method(s), and is not limited to any specific invention or inventions. The selected claims that are appended to this description define specific inventions included in the described apparatus and or methods. No single feature or element, or combination thereof, is essential to all possible combinations that may now or later be claimed.

As mentioned, a multiplexer is a network that separates signals from a common port to other ports, sorted according to frequency. Any number of other ports may be used. Referring toFIG. 1, a multiplexer10is shown. In this example, multiplexer10may be a diplexer12or a triplexer14. A common port or terminal16and a plurality of separate signal ports or terminals18are shown. Separate signal terminals18, in this example, may include a first signal terminal20, a second signal terminal22, and a third signal terminal24. First terminal20may be for conducting a signal having a first frequency F1. Second terminal22may be for conducting a signal having a second frequency F2. Third terminal24may be for conducting a signal having a third frequency F3. Frequencies F1, F2, and F3may all be different, and may be frequencies in non-overlapping frequency bands. As a diplexer12, in addition to common terminal16multiplexer10may have only signal terminals20and22or only signal terminals20and24.

Multiplexer10may provide isolation between first terminal20and terminals22and24by providing a high-impedance network26that, for signals having a frequency F1, consists of a low-impedance circuit30from terminals22and24to circuit ground32and an impedance-transforming network27between terminal20and terminals22and24. In this example, impedance-transforming network27consists of a transmission line28, and high-impedance network26may present at frequency F1an impedance at terminal20that is more than twice the characteristic impedance of the associated transmission line28. Circuit30may present at terminals22and24an impedance to circuit ground32that is less than one-half the characteristic impedance of transmission line28. Transmission line28has a first end28acoupled to terminal20and common terminal16, and a second end28bcoupled to terminals22and24. Transmission line28may have an electrical length equal to about a quarter of a wavelength (λ) of a signal having frequency F1. Transmission line28may have a characteristic impedance, such as 50 ohms.

A transmission line may be simple (formed of a single element) or compound (formed of plural elements). As used herein, a simple or real transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic waves, and which may be characterized by characteristic impedance, transmission-time delay, phase shift, and/or other parameter(s). A compound transmission line, also referred to as an artificial transmission line, may be a four-terminal electrical network that may have the characteristic impedance, transmission-time delay, phase shift, and/or other parameter(s) similar to a real transmission line and therefore can be used to emulate that of a real transmission line in one or more of these respects. Accordingly, transmission line28may be a simple or compound transmission line.

There are various ways that transmission lines may be implemented. Transmission lines may be a network of one or more sections of each of a simple transmission line (T), an inductor (L), and/or a capacitor (C). A few non-exclusive examples of transmission lines include series (in signal line) T; series L-shunt (to ground) C-series L; shunt C-series L-shunt C; series T-shunt C-series T; shunt C-series T-shunt C; and series L-shunt T-series L. Other networks may also be used.

Low-impedance circuit30may have low impedance for a signal having a frequency F1. Circuit30has low impedance relative to the characteristic impedance of an associated transmission line, such as in this case, transmission line28. For example, low-impedance may be impedance that is less than one-half of the characteristic impedance of transmission line28.

As is well known, a transmission line that is electrically an odd number of quarter wavelengths long terminated in an impedance ZLOADat the far end presents an input impedance ZIN=Z02/ZLOAD. Thus, the smaller ZLOADis, the larger ZINis. If ZLOADis effectively a short at a given frequency, then the combination of the transmission line and the short will effectively appear to be an open circuit at the input end. Thus, to produce higher impedance at common terminal16, low-impedance circuit30may be a short circuit34.

A short circuit is a circuit producing a relatively low impedance between two points of different potential in a circuit, and ideally has zero impedance. When the term is used in association with a related transmission line having a characteristic impedance at a given frequency, a short-circuit impedance may be considered to be an impedance that is less than ten percent of the characteristic impedance at the given frequency.

To the extent that a signal having a frequency F1reaches transmission line end28b, low-impedance circuit30provides a low-impedance path to ground. The closer circuit30is to a short circuit at frequency F1, the less that signals having a frequency F1will be conducted to terminals22and24. This short brings the F1-signal voltage down to zero at the junction of the frequency F2line, shown as terminal22, and the frequency F3line, shown as terminal24, thereby preventing any frequency F1signal from reaching frequency F2and frequency F3terminals22and24.

A low-impedance circuit, including a short circuit, may be a network of any configuration of one or more of each of a transmission line (T), a capacitor (C) and an inductor (L) suitable for providing a desired impedance. Examples include the following series combinations: T-L-T-C-T; L-C-T; L-T-C; T-L-C; L-C; and C-L. Shunt circuits to ground may also include combinations ending in an open-ended transmission-line stub, such as T (λ/4); L-T; L-(T//(parallel to) C to ground), T-L-T; C-L-T; and L-C-T.

High-impedance network26may also be considered to be a merged filter36in that it filters out frequency F1signals in the common-signal path for both frequency F2and frequency F3signals. Transmission line28and low-impedance circuit30may also function as parts of a compound transmission line36for frequency F2signals and/or as a transmission line38for frequency F3signals. That is, transmission line28may provide series inductance, and low-impedance circuit30may provide shunt capacitance for these signals.

It is seen that multiplexer10comprises a common terminal16for conducting a signal having a first frequency F1and a signal having a second frequency F2or F3different from the first frequency F1; a first terminal20for conducting the signal having the first frequency F1, the first terminal20being electrically coupled to the common terminal16; a second terminal22or24for conducting a signal having a second frequency F2or F3, the second terminal22or24being electrically coupled to the common terminal16; a first transmission line28having a first end28acoupled to the first terminal20and a second end28bcoupled to the second terminal22or24, the first transmission line28having an electrical length substantially equal to a quarter wavelength of the first frequency F1and a first characteristic impedance at the first frequency F1; and a first low-impedance circuit30electrically directly connecting the second end28bof the first transmission line28to a circuit ground32, the first low-impedance circuit30providing at the first frequency F1an impedance that is less than half of the first characteristic impedance, and the series combination of the first transmission line28and the first low-impedance circuit30providing at the first frequency F1a high impedance to ground32at the first end28aof the first transmission line28.

FIG. 2illustrates an example of multiplexer10, in the form of a triplexer40suitable for use in a mixer42. Elements in common with multiplexer10are assigned the same reference numbers as for multiplexer10. The description of these elements with regard toFIG. 1applies to triplexer40. In this embodiment, frequency F1is a radio frequency (RF), frequency F2is a local-oscillator (LO) frequency, and frequency F3is an intermediate frequency (IF). As a further example, for an E-band second-harmonic mixer, the RF signal may be in the range of 71 to 95 GHz, the LO signal may be in the range of 27 to 48 GHz, and the IF signal may be in the range of 1 to 16 GHz.

Triplexer40may include a terminating network44connecting common terminal16to circuit ground32. Terminating network44may provide suitable impedance to ground, such as a low impedance or short circuit. In this example, network44includes diodes46and48connected in parallel. These diodes are oppositely connected to provide signal conduction in both directions. Diodes46and48may provide parasitic capacitance to ground at lower frequencies, or inductance or resistance at higher frequencies.

Other terminating networks may also be provided. For example, an RF filter or an IF filter may also be located between the common terminal16and circuit ground32in multiplexer10shown inFIG. 1, or such as between the diode circuit and circuit ground inFIG. 2. As such, the side of the diode pair connected to common terminal16may electrically function as a ground at the pass frequency of the filter connected to the other side of the diode pair. Also, a single diode, a diode ring, or a switch network may be used, as is well known.

As with multiplexer10illustrated inFIG. 1, high-impedance network26may include transmission line28having an electrical length of λ/4 at radio frequency and low-impedance circuit30. The high-impedance network may provide high impedance to ground at end28aof the transmission line. If circuit30is a short circuit34, then the high-impedance network26appears as an open circuit at radio frequency.

FIG. 3illustrates a block diagram of an example of multiplexer10in the form of a triplexer50that includes triplexer14. Triplexer50thus may include common terminal16and signal terminals18, including frequency-F1signal terminal20, frequency-F2signal terminal22, and frequency-F3signal terminal24. A high-impedance network26may include transmission line28, with ends28aand28b, and frequency-F1low-impedance circuit30, which may be in the form of a short circuit34, coupled to circuit ground32. Terminating network44, which may be a capacitive load, may be coupled to circuit ground32.

Additionally, triplexer50may include a first-frequency signal line52coupling signal terminal20to common terminal16, a second-frequency line54coupling signal terminal22to common terminal16, and a third-frequency line56coupling signal terminal24to common terminal16. Signal line52may include a frequency-F3-blocking circuit58in series with a transmission line60. Blocking circuit58may be coupled to common terminal16. This blocking circuit may be any circuit or network appropriate to block signals having a frequency F3, while allowing transmission of signals having a frequency F1. A blocking circuit may be as simple as a capacitor or something more complex, such as an inductor in parallel with a capacitor to form a resonator.

In this example, transmission line60has an end60acoupled to terminal20, and may have an electrical length about equal to a quarter of a wavelength of a signal having a frequency F2. End60ais coupled to circuit ground32by a low-impedance circuit62. Low-impedance circuit62may be a short circuit64at frequency F2. Transmission line60and low-impedance circuit62may form a high-impedance network66. Similar to network26, network66may provide high impedance at a second end60bof transmission line60to signals having a frequency F2. Also similarly to low-impedance circuit30, low-impedance circuit62may provide low impedance to ground, such as a short circuit64, for signals having a frequency F2.

Blocking circuit58thus attenuates or even blocks signals having a frequency of F3from getting to terminal20, and high-impedance network66attenuates or blocks signals having a frequency of F2from getting to terminal20.

It is seen that triplexer50, as a form of multiplexer10, further comprises a second transmission line60having a first end60bcoupled to the common terminal16and a second end60acoupled to the first terminal20, the second transmission line60having an electrical length substantially equal to a quarter wavelength of the second frequency F2; and a second low-impedance circuit62electrically directly connecting the second end60aof the second transmission line60to the circuit ground32, the second low-impedance circuit62providing at the second frequency F2a second low impedance, and the series combination of the second transmission line60and the second low-impedance circuit62providing at the second frequency F2a second high impedance to ground at the first end60bof the second transmission line60.

Triplexer50may also include a third high-impedance network68that includes a transmission line70and a low-impedance circuit72. In this example, a first end70aof transmission line70is connected to second end28bof transmission line28, the third transmission line70also having an electrical length substantially equal to a quarter wavelength of the second frequency F2. Low-impedance circuit72electrically directly connects a second end70bof the transmission line70to the circuit ground32. Low-impedance circuit72may provide low impedance at the second frequency F2. If the impedance is low enough, circuit72may be a short circuit74at second frequency F2. The series combination of the second transmission line70and low-impedance circuit72may provide at the second frequency F2high impedance to ground at the first end70aof transmission line70.

Triplexer50may also be configured so that low-impedance circuits30and72provide capacitive impedance to ground at the third frequency F3and transmission lines28and70provide inductive impedance at the third frequency F3. Low-impedance circuits30and72and transmission lines28and70thereby form in combination transmission line38at third frequency F3. When terminating network44is a capacitive load at frequency F3, terminating network44may also form part of transmission line38.

A series low-impedance circuit76may be disposed in signal line54between second end28bof transmission line28and second terminal22, as shown. Low-impedance circuit76may provide low impedance at the second frequency F2. If the impedance is low enough, circuit76may be a short circuit78at second frequency F2.

A low-impedance circuit80may electrically directly connect signal line54, between second terminal22and circuit76, to the circuit ground32. Low-impedance circuit80may provide low impedance at the second frequency F2. If the impedance is low enough, circuit72may be a short circuit82at second frequency F2.

Triplexer50may also be configured so that low-impedance circuits30and80are configured to provide capacitive impedance to ground at the second frequency F2, and series low-impedance circuit76and transmission line28may be configured to provide inductive impedance at the second frequency F2. Low-impedance circuits30,76, and80and transmission line28may form in combination transmission line36between second terminal22and common terminal16at second frequency F2. A capacitive load provided by terminating network44may also form part of transmission line36.

FIGS. 4-6illustrate a mixer90as an example of multiplexer10and/or triplexer50.FIG. 4is a block diagram, andFIG. 5is a circuit schematic.FIG. 6is a simplified plan view showing an exposed mask layer of an E-band harmonic mixer90fabricated with the triplexer architecture described. As discussed previously with regard to multiplexer10and triplexer50, mixer90may include common terminal16, signal terminals18, including frequency-F1signal terminal20, frequency-F2signal terminal22, and frequency-F3signal terminal24, signal lines52,54, and56, transmission lines28,36,38,60, and70, low-impedance circuits30,62,72,76, and80, short circuits34,64,74,78, and82, high-impedance circuits26,66, and68, terminating network44, including diodes46and48, blocking circuit58, and circuit ground32. The previous descriptions of these features apply with frequencies F1, F2, and F3corresponding respectively to radio frequency (RF), local-oscillator frequency (LO), and intermediate frequency (IF). Transmission lines28,60, and70have respective ends28a,28b,60a,60b,70a, and70b, as discussed previously.

In addition, at each terminal there may be an impedance-matching network to match the impedance of the associated signal line with the impedance of the associated external circuit, not shown. Each matching network may be any network of transmission lines, inductances, and capacitances that provide the desired impedance. Specifically, an RF matching network92in signal line52is connected to RF terminal20; an LO matching network94in signal line54is connected to LO terminal22; and an IF matching network96in signal line56is connected to IF terminal24.

In this example, as particularly shown inFIGS. 5 and 6, matching network92includes a series transmission line98connected to terminal20. A shunt capacitor100connects the junction between transmission lines60and98to ground32. Matching network94includes a series transmission line102connected to terminal22. A shunt capacitor104connects to ground the junction between transmission line102and terminal22, as shown. Matching network96includes a series transmission line106connected to terminal24. A shunt open-ended transmission-line stub108capacitively couples to ground the junction between transmission line106and terminal24.

LO short circuit64includes a transmission line110in series with a capacitor112to ground. IF blocking circuit58includes a series capacitor114. RF short circuit34includes a transmission line116and a capacitor118to ground. LO short circuit74includes a transmission line120and a capacitor122to ground. Series LO short circuit78includes a transmission line124in series with a capacitor126connected to the junction with IF signal line56between transmission line28and RF short circuit34. IF short circuit82includes a transmission line128and a capacitor130to ground.

Generally referring toFIG. 6, mixer90may be formed with microstrip conductive traces132on and in a base dielectric substrate134including one or a plurality of layers and a backside ground plane, as is well known. In the embodiment shown, multiple layers of conductors connected by vias are used. Monolithic circuit structures, printed circuit boards, and other architectures may be used, as are also well known. In the structure shown, terminating network44may be provided as a flip chip136mounted on corresponding bonding pads138,139,140, and141. Other terminating network configurations and architectures may be used. For example, the network may be provided with separate components each connected to associated pads or other terminals, such as by bond wires, and other conventional forms of mounting components may be used.

It will be appreciated that mixer90channels the LO input signal power to the common terminal while limiting the amount of LO power reaching the RF and IF terminals, channels the RF signal to or from the common terminal with limited loss and with limited RF signal power reaching the LO or IF terminals, and channels the IF signal to or from the common terminal with limited loss and with limited IF signal power reaching the LO or RF terminals.

The RF short brings the RF voltage down to nearly zero at the junction of the LO and IF lines, thereby limiting the amount of RF signal reaching the LO and IF terminals. As has been mentioned, transmission line28, being a quarter wavelength long at the RF frequency, transforms the RF short impedance to a high impedance at the common terminal further reducing the amount of RF power reaching the junction between the LO and IF lines.

Similarly, the IF short on the LO line and the IF block on the RF line limit the amount of IF power reaching the LO and RF terminals. Furthermore, the LO short in series with the LO line may be configured to present a high impedance at the IF, further minimizing the leakage of IF into the LO terminal. Thus, IF signal power can flow between the IF terminal and the common terminal, but very little if any IF signal power presents itself at the LO and RF terminals.

The use of LO shorts on the RF and IF lines, as well as the associated use of transmission lines that are approximately a quarter wavelength long at the LO frequency, transform these shorts to high impedances to further reduce the LO power entering the RF and IF lines.

The IF short acts as a large inductance, and hence a high impedance, at the LO frequency. It therefore has little influence on transmission of the LO signal. The RF short acts as a capacitor to ground at the LO frequency, and the load on the common terminal (such as the diodes) can also present capacitance to ground. The LO short in series with the LO line and the quarter-wave line at RF can be adjusted to have the right amount of inductance to turn the network into a transmission line36for the LO band. This makes the LO match well over a wide bandwidth. An LO matching network may make further corrections to prevent LO signals from being reflected from the circuit and to help direct LO power into the common terminal.

Similarly, the LO short on the IF line, the RF short, and the capacitive load parasitics on the common terminal act as capacitors to ground in the IF path, and the inductance of the quarter-wave line for LO and the quarter-wavelength line at RF may be adjusted to turn the IF path to the common node into artificial transmission line38over the IF band. An additional IF matching network96can act to improve the match.

The LO short on the RF line may act as an inductor at the RF frequency, and it can be compensated by some parallel capacitance, such as capacitor100, in the RF matching network92to provide a broadband transmission line for RF signals from the RF terminal to the common terminal.

The matching networks can be implemented in many ways, but a simple way includes an inductance in series with the signal path and a capacitance from the signal path to ground. The capacitance can be on either side of the inductor, depending on the impedance to be matched.

The circuit may be adjusted to support the particular application in which it is to be used. Once the initial design is set, the circuit can be optimized with a circuit simulator to achieve desired performance goals over the prescribed RF, LO, and IF bands. The shorts, blocks, and transmission lines as optimized may deviate somewhat from their namesakes over the various frequency bands, but the circuit architecture will be basically intact.

The above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. Accordingly, while embodiments of multiplexers and mixers, and associated methods of multiplexing signals have been particularly shown and described, many variations may be made therein. This disclosure may include one or more independent or interdependent inventions directed to various combinations of features, functions, elements, and/or properties, one or more of which may be defined in the following claims. Other combinations and sub-combinations of features, functions, elements, and/or properties may be claimed later in this or a related application. Such variations, whether they are directed to different combinations or directed to the same combinations, whether different, broader, narrower, or equal in scope, are also regarded as included within the subject matter of the present disclosure. An appreciation of the availability or significance of claims not presently claimed may not be presently realized. Accordingly, the foregoing embodiments are illustrative, and no single feature or element, or combination thereof, is essential to all possible combinations that may be claimed in this or a later application. Each claim defines an invention disclosed in the foregoing disclosure, but any one claim does not necessarily encompass all features or combinations that may be claimed. Where the claims recite “a” or “a first” element or the equivalent thereof, such claims include one or more such elements, neither requiring nor excluding two or more such elements. Further, ordinal indicators, such as first, second, or third, for identified elements are used to distinguish between the elements, and do not indicate a required or limited number of such elements, and do not indicate a particular position or order of such elements unless otherwise specifically stated.

INDUSTRIAL APPLICABILITY

The methods and apparatus described in the present disclosure are applicable to telecommunications and other industries utilizing signal processing.