Reducing pass-band ripple in radio-frequency (RF) filters used for pass-band filtering in a wireless communications system

An electronically tunable equalizer is provided to a downlink (DL) and/or uplink (UL) signal processing path of a wireless communication unit incorporating a RF filter. The electronically tunable equalizer is pre-configured with a plurality of capacitance states, each representing a specific capacitance. The equalizer produces a different equalizer response for each of the plurality of capacitance states based on a received pass-band frequency signal. The plurality of equalizer responses is provided to the RF filter on a signaling processing path, thus affecting the RF filter's pass-band ripple. The RF filter's pass-band ripple is measured for each of the plurality of equalizer responses to determine a desired pass-band ripple. By configuring the electronically tunable equalizer to the capacitance state that produced the desired pass-band ripple, a ceramic RF filter may be used in the wireless communication unit for the benefit of lower cost and size, with reduced pass-band ripple.

BACKGROUND

The disclosure relates generally to wireless communications systems that support distributing communications services to remote units, and more particularly to reducing radio-frequency (RF) pass-band ripple in RF filters used for pass-band filtering of RF communications signals in wireless communication systems, including but not limited to distributed antenna system (DASs).

Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, local area wireless services (e.g., so-called “wireless fidelity” or “WiFi” systems) and wide area wireless services are being deployed in many different types of areas (e.g., coffee shops, airports, libraries, etc.). Distributed communications or antenna systems communicate with wireless devices called “clients,” “client devices,” or “wireless client devices,” which must reside within the wireless range or “cell coverage area” in order to communicate with an access point device. Distributed antenna systems are particularly useful to be deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive RF signals from a source, such as a base station for example. Example applications where DASs can be used to provide or enhance coverage for wireless services include public safety, cellular telephony, wireless local access networks (LANs), location tracking, and medical telemetry inside buildings and over campuses.

One approach to deploying a DAS involves the use of RF antenna coverage areas, also referred to as “antenna coverage areas.” Antenna coverage areas can be formed by remotely distributed antenna units, also referred to as remote units (RUs). The remote units each contain or are configured to couple to one or more antennas configured to support the desired frequency(ies) or polarization to provide the antenna coverage areas. Antenna coverage areas can have a radius in the range from a few meters up to twenty meters as an example. Combining a number of remote units creates an array of coverage areas. Because the antenna coverage areas each cover small areas, there typically may be only a few users (clients) per antenna coverage area. This arrangement generates a uniform high quality signal enabling high throughput supporting the required capacity for the wireless system users.

As an example,FIG. 1illustrates distribution of communications services to coverage areas10(1)-10(N) of a DAS12, wherein ‘N’ is the number of coverage areas. These communications services can include cellular services, wireless services such as RFID tracking, Wireless Fidelity (WiFi), local area network (LAN), WLAN, and combinations thereof, as examples. The coverage areas10(1)-10(N) may be remotely located. In this regard, the remote coverage areas10(1)-10(N) are created by and centered on remote antenna units14(1)-14(N) connected to a central unit16(e.g., a head-end controller or head-end unit). The central unit16may be communicatively coupled to a base station18. In this regard, the central unit16receives downlink RF communications signals20D from the base station18to be distributed to the remote antenna units14(1)-14(N). The remote antenna units14(1)-14(N) are configured to receive downlink communications signals20D from the central unit16over a communications medium22to be distributed to the respective coverage areas10(1)-10(N) of the remote antenna units14(1)-14(N). Each remote antenna unit14(1)-14(N) may include an RF transmitter/receiver (not shown) and a respective antenna24(1)-24(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices26within their respective coverage areas10(1)-10(N). The remote antenna units14(1)-14(N) are also configured to receive uplink RF communications signals20U from the client devices26in their respective coverage areas10(1)-10(N) to be distributed to the base station18. The size of a given coverage area10(1)-10(N) is determined by the amount of RF power transmitted by the respective remote antenna unit14(1)-14(N), the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the client device26. Client devices26usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the remote antenna units14(1)-14(N) mainly determine the size of their respective remote coverage areas10(1)-10(N).

With continuing reference toFIG. 1, the remote antenna units14(1)-14(N) operate within a specific bandwidth in a specific RF spectrum or spectrums based on the supported communications services. This RF spectrum or spectrums is also known as pass-band frequency(ies). For instance, if a particular remote antenna unit14in the DAS10inFIG. 1is configured to support Wi-Fi communications services, the remote antenna unit14may be configured to distribute downlink and uplink RF communications signals20D,20U in the pass-band between 2402 MHz and 2422 MHz in Industrial, Scientific, and Medical (ISM) band in the United States. Non-supported RF signals outside the pass-band may be suppressed to minimize interference to adjacent frequency bands. The client device26is configured to receive the downlink RF communications signals20D in the pass-band frequency from the remote antenna units14(1)-14(N) and suppress RF signals outside (e.g., above or below) the pass-band frequency so as to improve receiver sensitivity and performance. Also, the client device26is configured to transmit uplink RF communications signals20U in a designated pass-band frequency to the remote antenna units14(1)-14(N). Thus, RF transmitters and receivers in the remote antenna units14(1)-14(N) can incorporate RF filters to pass desired downlink and uplink RF communications signals20D,20U within the pass-band frequency while attenuating unwanted RF communications signals outside (e.g., above or below) the pass-band frequency.

One type of RF filter that can be employed in the remote units14(1)-14(N) to pass desired downlink and uplink RF communications signals20D,20U is a cavity RF filter. A cavity RF filter can provide high RF isolation to adjacent frequency bands of the pass-band and produce a relatively flat frequency magnitude response inside the pass-band. Another type of RF filter that can be employed in the remote antenna units14(1)-14(N) to pass desired downlink and uplink RF communications signals20D,20U is a ceramic RF filter. A ceramic RF filter can also provide high RF isolation. Ceramic RF filters have cost and size advantages over cavity RF filters. However, a ceramic RF filter may suffer significant ripple in the pass-band frequency magnitude response compared to a cavity RF filter with the same bandwidth and out-of-band attenuation.

Ripple refers to fluctuations (measured in dB) in the pass-band of a RF filter's frequency magnitude response curve. In contrast to flat pass-band frequency magnitude response, ripple in a pass-band means that RF signals across the entire pass-band bandwidth will have different gains. For a downlink signal, some portions of the pass-band frequency signal will exhibit higher gain and therefore the downlink signal at these portions of the pass-band will be transmitted with higher power while other portions of the pass-band will exhibit lower gain and therefore the downlink signal at these portions of the pass-band will be transmitted with lower power. Having an equal gain across the entire pass-band bandwidth is important for getting the optimal performance. Because a RF transmitter's maximum transmit power is strictly limited by regulatory requirements, RF signals transmitted on frequencies with higher gains can maximize the output power without increasing the transmit power. RF coverage in the coverage areas10(1)-10(N) in the DAS12inFIG. 1will suffer as result of the uneven gains caused by ripple.

No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy of any cited documents.

SUMMARY

Embodiments disclosed in the detailed description include reducing pass-band ripple in radio-frequency (RF) filters used for pass-band filtering in a wireless communications system. As disclosed herein, an electronically tunable equalizer is provided to a downlink (DL) and/or uplink (UL) signal processing path of a wireless communication unit incorporating a RF filter. The equalizer has an electronically tunable capacitor circuit pre-configured with a plurality of different capacitance states each representing a specific capacitance in the electronically tunable capacitor circuit. For each of the plurality of different capacitance states, the electronically tunable equalizer generates a different weighted pass-band frequency response (“equalizer response”). By combining an equalizer response generated by the electronically tunable equalizer with a native frequency response of the RF filter on the DL and/or UL signal processing path in the wireless communication unit, a pass-band ripple in a filtered pass-band frequency signal generated by the RF filter can be modified. The equalizer can be tuned to a desired capacitance state to generate a desired equalizer response that produces a reduced pass-band ripple in the filtered pass-band frequency signal, as desired. This allows a ceramic RF filter to be used in the wireless communication unit for the benefit of lower cost and size, over a cavity RF filter for example, with reduced pass-band ripple for improved performance.

To determine the desired capacitance state for the electronically tunable equalizer, at each of the plurality of different capacitance states, the electronically tunable equalizer can be electronically tuned to generate a plurality of different equalizer responses for pass band frequency signals. The pass-band ripple in the filtered pass-band frequency signal is measured for each of the plurality of different equalizer responses to determine which equalizer response produces the desired reduced pass-band ripple in the filtered pass-band frequency signal.

One embodiment of the disclosure relates to a RF pass-band ripple tuning system for reducing pass-band ripple introduced by a RF filter in a wireless communications system. The RF pass-band ripple tuning system comprises an electronically tunable equalizer and a RF filter. The electronically tunable equalizer comprises a pass-band RF signal input, at least one resonator, an electronically tunable capacitor circuit, a weighted pass-band RF signal output, and an attenuator. The pass-band RF signal input is configured to receive a wireless pass-band signal. The at least one resonator is coupled to the pass-band RF signal input configured to generate at least one resonance frequency on at least one resonator output based on the wireless pass-band frequency signal and at least one internal capacitance. The electronically tunable capacitor circuit comprises a plurality of capacitance states, a capacitance state input, and a capacitance state selector. The capacitance state input is configured to receive a selected capacitance state among the plurality of capacitance states. The capacitance state selector is configured to couple the selected capacitance state received from the capacitance state input to the at least one resonator to modify the at least one resonance frequency on at least one resonator output based on the selected capacitance state. The resonator output is coupled to a weighted pass-band RF signal output to provide a weighted pass-band frequency signal for the wireless pass-band frequency signal received on the pass-band RF signal input. The attenuator is coupled across the pass-band RF signal input and the weighted pass-band RF signal output. The RF filter is configured to receive the weighted pass-band frequency signal and filter the weighted pass-band frequency signal in the wireless pass-band frequency signal to generate a filtered pass-band frequency signal.

An additional embodiment of the disclosure relates to a method for reducing pass-band ripple in a RF filter in a wireless communication system. The method comprises for each next capacitance state among a plurality of capacitance states in an electronically tunable equalizer, instructing an electronically tunable equalizer to select a next capacitance state among the plurality of capacitance states. For each next frequency step among a plurality of frequency steps of a received pass-band frequency signal, the method further comprises receiving a pass-band frequency signal defined by a next frequency step, generating a weighted pass-band frequency signal for the pass-band frequency signal defined by the next frequency step for the next capacitance state, passing the weighted pass-band frequency signal through a RF filter to generate a filtered pass-band frequency signal defined by the next frequency step for the next capacitance state, measuring a next output power level of the filtered pass-band frequency signal, and storing the next output power level of the filtered pass-band frequency signal defined by the next frequency step for the next capacitance state. After generating the filtered pass-band frequency signals for the pass-band frequency signals defined by each of the plurality of frequency steps, the method further comprises calculating and storing a next pass-band ripple for the next capacitance state based on stored output power levels of the filtered pass-band frequency signal. After measuring and storing the pass-band ripples for each of the plurality of capacitance states in the electronically tunable equalizer, the method further comprises selecting a desired pass-band ripple from stored pass-band ripples and configuring the electronically tunable equalizer to a capacitance state produced the desired pass-band ripple.

An additional embodiment of the disclosure relates to a non-transitory computer-readable medium having stored thereon computer executable instructions. The computer executable instructions cause an electronically tunable equalizer in a radio-frequency (RF) pass-band ripple tuning system to adjust a pass-band ripple in a RF filter in a wireless communications system, by, for each next capacitance state among a plurality of capacitance states in an electronically tunable equalizer, instructing the electronically tunable equalizer to select a next capacitance state among the plurality of capacitance states. The computer executable instructions also cause the electronically tunable equalizer, for each next frequency step among a plurality of frequency steps of a received pass-band frequency signal, to measure a next output power level of a filtered pass-band frequency signal generated by a RF filter based on a weighted pass-band frequency signal generated by the electronically tunable equalizer for the next frequency step for the next capacitance state, to provide a next filter output power level for the filtered pass-band frequency signal, and storing the next output power level of the filtered pass-band frequency signal defined by the next frequency step for the next capacitance state. The computer executable instructions also cause the electronically tunable equalizer to, for the next capacitance state among the plurality of capacitance states in an electronically tunable equalizer, calculate a next pass-band ripple for the next capacitance state based on stored output power levels of the filtered pass-band frequency signal, and store the next pass-band ripple for the next capacitance state. The computer executable instructions also cause the electronically tunable equalizer to select a desired pass-band ripple from stored pass-band ripples, and configure the electronically tunable equalizer to a capacitance state produced the desired pass-band ripple.

DETAILED DESCRIPTION

Various embodiments will be further clarified by the following examples. A wireless communication system includes radio-frequency (RF) filters for various purposes. One type of RF filter is known as a band-pass filter, which works on a downlink (DL) or a uplink (UL) signal processing path in a wireless communication equipment to pass desired RF signals inside a predefined frequency range (“pass-band frequency”) and reject unwanted RF signals outside the predefined frequency range. For example, a cavity filter and a ceramic filter can both be configured to provide the band-pass filter functionalities. In many real-world implementations, the ceramic filter may be more preferable than the cavity filter because the ceramic filter is smaller and less expensive than the cavity filter. One of the known shortcomings of the ceramic filter is that the ceramic filter generates larger ripple in a pass-band frequency signal than the cavity filter does in the pass-band frequency signal, thus negatively impacting RF coverage and RF receiver performance. Hence, it is desirable to reduce ceramic filter pass-band ripple for improved RF performance in the wireless communication system.

In aspects disclosed herein, an electronically tunable equalizer is provided to a DL and/or UL signal processing path of a wireless communication unit incorporating a RF filter. The electronically tunable equalizer has an electronically tunable capacitor circuit pre-configured with a plurality of different capacitance states each representing a specific capacitance in the electronically tunable capacitor circuit. For each of the plurality of different capacitance states, the electronically tunable equalizer generates a different weighted pass-band frequency response (“equalizer response”). By combining an equalizer response generated by the electronically tunable equalizer with a native frequency response of the RF filter on the DL and/or UL signal processing path in the wireless communication unit, a pass-band ripple in a filtered pass-band frequency signal generated by the RF filter can be modified. The electronically tunable equalizer can be tuned to a desired capacitance state to generate a desired equalizer response that produces a reduced pass-band ripple in the filtered pass-band frequency signal, as desired. This allows, for example, a ceramic RF filter to be used in the wireless communication unit for the benefit of lower cost and size, over a cavity RF filter for example, with reduced pass-band ripple for improved performance.

In this regard,FIG. 2provides a schematic diagram of an exemplary RF pass-band ripple tuning system. The RF pass-band ripple tuning system28comprises a wireless communication unit30in this example. The wireless communication unit30is tuned to generate a desired pass-band ripple by equalizing pass-band ripple to a required level. In this regard, a RF pass-band ripple tuning controller32is provided that controls an electronically tunable equalizer34. The electronically tunable equalizer34is controlled by RF pass-band ripple tuning controller32so as to generate a desired frequency response to reduce pass-band ripple introduced by an RF filter36. The RF filter36is configured to filter a pass-band frequency signal38input into the wireless communication unit30. For example, the RF filter36may be a ceramic RF filter that can provide high out-of-band attenuation or high uplink RF isolation, but may also suffer significant ripple. Thus, the RF pass-band ripple tuning system28is employed to reduce the ripple introduced by the RF filter36. In this regard, aspects of the RF pass-band ripple tuning system28are described next, followed by descriptions of the RF pass-band ripple tuning controller32.

With continuing reference toFIG. 2, the equalizer34includes an electronically tunable capacitor circuit40and at least one resonator42(“resonator42”). The electronically tunable capacitor circuit40is configured with a plurality of capacitance states44(1)-44(N). Each of the plurality of capacitance states44(1)-44(N) corresponds to a specific capacitance. In this example, each plurality of capacitance states44(1)-44(N) has a different capacitance. A capacitance state selector45is provided in the electronically tunable equalizer34that is configured to select a capacitance state among the plurality of capacitance states44(1)-44(N) based on a capacitance state input46received from the RF pass-band ripple tuning controller32. By the electronically tunable capacitor circuit40being coupled to the at least one resonator42, the capacitance state selected by the capacitance state selector45among the plurality of capacitance states44(1)-44(N) modifies at least one resonance frequency of the at least one resonator42. When the electronically tunable equalizer34generates a weighted pass-band frequency signal48based on the received pass-band frequency signal38, the weighted pass-band frequency signal48has a frequency response (“equalizer response”) that is modified by the at least one resonator frequency generated by the at least one resonator42. The RF filter36, on the other hand, has a native frequency response (“filter response”).

A frequency response is a quantitative measurement of a wireless system's or device's gain and phase changes in an operating frequency band. The frequency response may be plotted as a curve that shows the gain of the wireless system or device measured in decibels (dB) versus a frequency of the signals, measured in Hertz (Hz), that is fed to the wireless system or device, as can be seen inFIGS. 3A-3Cdiscussed below.

In this regard,FIGS. 3A and 3Bare exemplary frequency response plots illustrating pass-band frequency responses in relation to the electronically tunable equalizer34and the RF filter36inFIG. 2. Specifically,FIG. 3Ais an exemplary plot50of the filter response that is native to the RF filter36. InFIG. 3A, the filter response51generated by the RF filter36has a relatively large ripple52.FIG. 3Bis an exemplary plot53of the equalizer response generated by the equalizer34. The equalizer response54inFIG. 3Bis generated by the equalizer34based on the configuration and operation ofFIG. 2. When the electronically tunable capacitor circuit40is tuned among the plurality of capacitance states44(1)-44(N), the shape and the magnitude of the equalizer response54inFIG. 3Bchanges accordingly.

With reference back toFIG. 2, the weighted pass-band frequency signal48generated by the electronically tunable equalizer34is provided to the RF filter36. The RF filter36filters the weighted pass-band frequency signal48to generate a filtered pass-band frequency signal49with reduced ripple. The filtered pass-band frequency signal49has a frequency response (“combined response”) that is a combination of the equalizer response and the filter response. Ideally, there should be smaller ripple in the filtered pass-band frequency signal49, because the equalizer response acts to offset the ripple in the filter response. This is shown inFIG. 3C, which is an exemplary plot56of the combined response58of the filtered pass-band frequency signal49. As can be seen inFIG. 3C, the equalizer response58helps smooth out an otherwise larger ripple54associated with the filter response52, thus producing a much smaller ripple60in the combined response58. Clearly, the equalizer response58generated by the electronically tunable equalizer35can effectively modify the filter response52generated by the RF filter36, thus effecting the combined response58in the filtered pass-band frequency signal49.

With continuing reference toFIG. 2, by having the electronically tunable equalizer34in the wireless communication unit30, it is possible to configure the electronically tunable capacitor circuit40to a desired capacitance state among the plurality of capacitance states44(1)-44(N) so that the wireless communication unit30will generate the filtered pass-band frequency signal49with a desired pass-band ripple, which is an aggregated effect of the electronically tunable equalizer34and the RF filter36. However, it is understandably difficult for the RF pass-band ripple tuning controller32to pinpoint the desired capacitance state among the plurality of capacitance states44(1)-44(N) without a proper process. In this regard,FIG. 4is a flowchart illustrating an exemplary RF pass-band ripple tuning process62for the RF pass-band ripple tuning controller32to determine the desired capacitance state among the plurality of capacitance states44(1)-44(N) for reducing the pass-band ripple in the wireless communication unit30. As will be described in more detail below, the RF pass-band ripple tuning process62instructs the capacitance state selector45to select each of the plurality of capacitance states44(1)-44(N) for the electronically tunable capacitor circuit40. For each selection, the RF pass-band ripple tuning controller32measures the pass-band ripple of the wireless communication unit30influenced by all of the plurality of capacitance states44(1)-44(N). The RF pass-band ripple tuning controller32can thus identify the desired capacitance state among the plurality of capacitance states44(1)-44(N) that produces the desired pass-band ripple for the unit30. In this regard,FIG. 4will be discussed in conjunction with components of the RF pass-band ripple tuning system28ofFIG. 2.

As shown inFIG. 4, the RF pass-band ripple tuning process62is a looped process designed to test the effect of each of the plurality of capacitance states44(1)-44(N) on the pass-band ripple of the filtered pass-band frequency signal49. The electronically tunable capacitor circuit40may be configured to have thirty-two (32) capacitance states indexed from44(1) to44(32) according to naming conventions used inFIG. 2, representing an exemplary capacitance range between 0.5 picofarad (pF) and 4.5 pF. The capacitance range is divided into thirty-one (31) incremental steps of one-hundred-twenty (120) femtofarad (IF). For example, capacitance state31(1) represents a capacitance of 0.5 pF, capacitance state31(2) represents a capacitance of 0.62 pF (0.5 pF plus 0.12 pF), and so on.

In this regard and with reference toFIG. 4, at the beginning of the RF pass-band ripple tuning process60, the capacitance state selector45configures the electronically tunable capacitor circuit40to a first capacitance state among the plurality of capacitance states44(1)-44(N) (block64), for example capacitance state44(1). Subsequently, the electronically tunable equalizer34is provided with a sub-portion of the pass-band frequency signal38associated with one of a plurality of frequency steps predetermined to divide the pass-band frequency signal38across a frequency range (e.g., bandwidth) into a plurality of sub-portions (block66). For example, if a frequency signal has a frequency range between 2402 megahertz (MHz) and 2422 MHz as in Wi-Fi channel one (1) in the United States, and if the frequency range is divided into twenty (20) frequency steps, then each frequency step represents a 2 MHz sub-portion of the frequency signal. In this regard, when the electronically tunable equalizer34is said to be provided with a frequency step, the electronically tunable equalizer34is really provided with the sub-portion of the pass-band frequency signal38that corresponds to the frequency step. In a non-limiting example, the electronically tunable equalizer34is provided with a frequency step among the plurality of frequency steps from the lowest frequency step to the highest frequency step.

When the sub-portion of the pass-band frequency signal38is provided to the electronically tunable equalizer34and in turn the RF filter36, the RF pass-band ripple tuning controller32can measure and record an output power level of the wireless communication unit30corresponding to the sub-portion of the pass-band frequency signal38(block68). The RF pass-band ripple tuning process62repeats the step of providing the next frequency step to the electronically tunable equalizer34(block66), and the step of measuring and recording a corresponding output power level of the RF filter36(block68) until each of the plurality of frequency steps has been provided to the electronically tunable equalizer34, and the corresponding output power level of the RF filter36are measured and recorded (block70). At this point, the RF pass-band ripple tuning controller32calculates and records a pass-band ripple for the current capacitance state (block72). In a non-limiting example, the pass-band ripple is calculated as the ratio (dB) of the highest recorded output power level of the RF filter36and the lowest recorded output power level of the RF filter36. If some of the capacitance states44(1)-44(N) remain to be tested (block74), the electronically tunable capacitor circuit40is then configured to a next capacitance state among the plurality of capacitance state44(1)-44(N) (block76) and so repeated until all of the plurality of capacitance states44(1)-44(N) are tested. At this point, the RF pass-band ripple tuning controller32has measured and recorded the pass-band ripple associated with all of the plurality of capacitance states44(1)-44(N). The RF pass-band ripple tuning controller42is thus able to identify a desired pass-band ripple among all recorded pass-band ripples and instructs the capacitance state selector45to configure the electronically tunable equalizer34to the capacitance state associated with the desired pass-band ripple (block78). At completion of the RF pass-band ripple tuning process62, the equalizer34is thus tuned to produce the desired pass-band ripple in the filtered pass-band frequency signal49.

With continuing reference toFIG. 4, the step of configuring the capacitor circuit40to a next capacitance state (block76) can be carried out in many possible ways. In a non-limiting example, selection of the next capacitance state may be in sequential ascending order. For example, the electronically tunable capacitor circuit40is set to the next capacitance state such as44(2),44(3), and so on. By the same example, if the electronically tunable capacitor circuit40has been configured up to capacitance state of44(N), the RF pass-band ripple tuning process62will come to an end since capacitance state44(N) is the highest order among the plurality of capacitance state44(1)-44(N). In another non-limiting example, the electronically tunable capacitor circuit40may be configured to start with any of the plurality of capacitance states44(1)-44(N) and select a next capacitance state in sequential descending, random, or other order. It is also possible for the RF pass-band ripple tuning controller32to stop the RF pass-band ripple tuning process62after testing only a subset of the plurality of capacitance states44(1)-44(N) as long as a desired pass-band ripple measure is obtained. Further, the RF pass-band ripple tuning process62may be performed while the wireless communication unit32is off-line (e.g., during testing, calibration, maintenance) or online (e.g., during real-time operation). Further, the RF pass-band ripple tuning controller32may be a self-contained entity (e.g., automatic test equipment) outside the wireless communication unit32or be integrated as part of the unit32.

In this regard,FIG. 5Ais a schematic diagram of another exemplary optical fiber-based distributed antenna system (DAS)80as an example of the wireless communication unit32that may include the RF pass-band ripple tuning controller32inFIG. 2for reducing pass-band ripple in RF filters used for pass-band filtering in the DAS80. In this embodiment, the optical fiber-based DAS80includes optical fiber for distributing RF communication services. The optical fiber-based DAS80in this embodiment is comprised of three (3) main components. One or more radio interfaces provided in the form of radio interface modules (RIMs)82(1)-82(M) in this embodiment are provided in head end equipment (HEE)84to receive and process downlink electrical RF communications signals86D(1)-86D(R) from one or more base stations87(1)-87(T) (shown inFIG. 5B) prior to optical conversion into downlink optical RF communications signals. The RIMs82(1)-82(M) provide both downlink and uplink interfaces. The notations “1-R” and “1-M” indicate that any number of the referenced component, 1-R and 1-M, respectively, may be provided. The RF pass-band ripple tuning controller32inFIG. 2can be included in the RIMs82(1)-82(M) or provided in the same location, housing, or packaging as the RIMs82(1)-82(M), for reducing pass-band ripple in RF filters used for pass-band filtering in the RIMs82(1)-82(M). As will be described in more detail below, the HEE84is configured to accept a plurality of RIMs82(1)-82(M) as modular components that can easily be installed and removed or replaced in the HEE84. In one embodiment, the HEE84is configured to support up to eight (8) RIMs82(1)-82(8).

Each RIM82(1)-82(M) can be designed to support a particular type of radio source or range of radio sources (i.e., frequencies) to provide flexibility in configuring the HEE84and the optical fiber-based DAS80to support the desired radio sources. For example, one RIM82may be configured to support the PCS radio band. Another RIM82may be configured to support the 700 MHz radio band. In this example, by inclusion of these RIMs82, the HEE84would be configured to support and distribute RF communications signals on both PCS and LTE700radio bands. RIMs82may be provided in the HEE84that support any frequency bands desired, including but not limited to the US Cellular band, Personal Communication Services (PCS) band, Advanced Wireless Services (AWS) band, 700 MHz band, Global System for Mobile communications (GSM)900, GSM1800, and Universal Mobile Telecommunication System (UMTS). RIMs82may be provided in the HEE84that support any wireless technologies desired, including but not limited to Code Division Multiple Access (CDMA), CDMA200, 1 xRTT, Evolution—Data Only (EV-DO), UMTS, High-speed Packet Access (HSPA), GSM, General Packet Radio Services (GPRS), Enhanced Data GSM Environment (EDGE), Time Division Multiple Access (TDMA), Long Term Evolution (LTE), iDEN, and Cellular Digital Packet Data (CDPD).

RIMs82may be provided in the HEE84that support any frequencies desired, including but not limited to US FCC and Industry Canada frequencies (824-849 MHz on uplink and 869-894 MHz on downlink), US FCC and Industry Canada frequencies (1850-1915 MHz on uplink and 1930-1995 MHz on downlink), US FCC and Industry Canada frequencies (1710-1755 MHz on uplink and 2110-2155 MHz on downlink), US FCC frequencies (698-716 MHz and 776-787 MHz on uplink and 728-746 MHz on downlink), EU R & TTE frequencies (880-915 MHz on uplink and 925-960 MHz on downlink), EU R & TTE frequencies (1710-1785 MHz on uplink and 1805-1880 MHz on downlink), EU R & TTE frequencies (1920-1980 MHz on uplink and 2110-2170 MHz on downlink), US FCC frequencies (806-824 MHz on uplink and 851-869 MHz on downlink), US FCC frequencies (896-901 MHz on uplink and 929-941 MHz on downlink), US FCC frequencies (793-805 MHz on uplink and 763-775 MHz on downlink), and US FCC frequencies (2495-2690 MHz on uplink and downlink).

The downlink electrical RF signals86D(1)-86D(R) are provided to a plurality of optical interfaces provided in the form of optical interface modules (OIMs)88(1)-88(N) in this embodiment to convert the downlink electrical RF signals86D(1)-86D(N) into downlink optical RF communications signals90D(1)-90D(R). The RF pass-band ripple tuning controller32inFIG. 2can also be included in the OIMs88(1)-88(N), or provided in the same location, housing, or packaging as the OIMs88(1)-88(N), for reducing pass-band ripple in RF filters used for pass-band filtering in the OIMs88(1)-88(N). The notation “1-N” indicates that any number of the referenced component 1-N may be provided. The OIMs88may be configured to provide one or more optical interface components (OICs) that contain O/E and E/O converters, as will be described in more detail below. The OIMs88support the radio bands that can be provided by the RIMs82, including the examples previously described above. Thus, in this embodiment, the OIMs88may support a radio band range from 400 MHz to 2700 MHz, as an example, so providing different types or models of OIMs88for narrower radio bands to support possibilities for different radio band-supported RIMs82provided in the HEE84is not required. Further, as an example, the OIMs88may be optimized for sub-bands within the 400 MHz to 2700 MHz frequency range, such as 400-700 MHz, 700 MHz-1 GHz, 1 GHz-1.6 GHz, and 1.6 GHz-2.7 GHz, as examples.

The OIMs88(1)-88(N) each include E/O converters to convert the downlink electrical RF communications signals86D(1)-86D(R) to downlink optical RF communications signals90D(1)-90D(R). The downlink optical RF communications signals90D(1)-90D(R) are communicated over downlink optical fiber(s)93D to a plurality of remote units provided in the form of remote antenna units (RAUs)92(1)-92(P). The notation “1-P” indicates that any number of the referenced component 1-P may be provided. O/E converters provided in the RAUs92(1)-92(P) convert the downlink optical RF communications signals90D(1)-90D(R) back into downlink electrical RF communications signals86D(1)-86D(R), which are provided over downlinks94(1)-94(P) coupled to antennas96(1)-96(P) in the RAUs92(1)-92(P) to client devices26in the reception range of the antennas96(1)-96(P). The RF pass-band ripple tuning controller32inFIG. 2can also be included in the RAUs92(1)-92(P), or provided in the same location, housing, or packaging as the RAUs92(1)-92(P), for reducing pass-band ripple in RF filters used for pass-band filtering in the RAUs.

E/O converters are also provided in the RAUs92(1)-92(P) to convert uplink electrical RF communications signals received from client devices26through the antennas96(1)-96(P) into uplink optical RF communications signals98U(1)-98U(R) to be communicated over uplink optical fibers93U to the OIMs88(1)-88(N). The OIMs88(1)-88(N) include O/E converters that convert the uplink optical RF communications signals98U(1)-98U(R) into uplink electrical RF communications signals100U(1)-100U(R) that are processed by the RIMs82(1)-82(M) and provided as uplink electrical RF communications signals102U(1)-102U(R). Downlink electrical digital signals103D(1)-103D(P), such as Ethernet signals, communicated over downlink electrical medium or media (hereinafter “medium”)105D(1)-105D(P) can be provided to the RAUs92(1)-92(P), such as from a digital data services (DDS) controller and/or DDS switch as provided by example inFIG. 5B, separately from the RF communication services, as well as uplink electrical digital signals103U(1)-103U(P) communicated over uplink electrical medium105U(1)-105U(P), as also illustrated inFIG. 5B. Common elements betweenFIGS. 5A and 5Bare illustrated inFIG. 5Bwith common element numbers. Power may be provided in the downlink and/or uplink electrical medium105D(1)-105D(P) and/or105U(1)-105U(P) to the RAUs.

FIG. 5Bis a schematic diagram of providing digital data services and RF communication services to RAUs and/or other remote communications units in the optical fiber-based DAS80ofFIG. 5A. Common components betweenFIGS. 5A and 5Bhave the same element numbers and thus will not be re-described. As illustrated inFIG. 5B, a power supply module (PSM)113may be provided to provide power to the RIMs82(1)-82(M) and radio distribution cards (RDCs)107that distribute the RF communications from the RIMs82(1)-82(M) to the OIMs88(1)-88(N) through RDCs109. In one embodiment, the RDCs107,109can support different sectorization needs. A PSM115may also be provided to provide power the OIMs88(1)-88(N). An interface111, which may include web and network management system (NMS) interfaces, may also be provided to allow configuration and communication to the RIMs82(1)-82(M) and other components of the optical fiber-based DAS80. A microcontroller, microprocessor, or other control circuitry, called a head-end controller (HEC)117may be included in HEE84to provide control operations for the HEE84. The RF pass-band ripple tuning controller32inFIG. 2may also be incorporated into or associated with one or more interconnect units (ICUs)116, as shown inFIG. 5B, for reducing pass-band ripple in RF filters used for pass-band filtering in the ICUs116provide power signals to the RAUs92(1)-92(P) or route information about other monitored signals to other components in the DAS80.

FIG. 6is a more detailed schematic diagram illustrating an exemplary RF pass-band ripple tuning system120that includes an electronically tunable equalizer34(1) provided in a wireless communication unit30(1) and controlled by a RF pass-band ripple tuning controller32(1) for reducing pass-band ripple in the wireless communication unit30(1). Elements ofFIG. 2are referenced in connection withFIG. 6and will not be re-described herein. According to one embodiment designed to perform RF pass-band ripple tuning on a DL path in a DAS remote unit, the exemplary RF pass-band ripple tuning system120comprises the wireless communication unit30(1) (“DAS RU”) and a RF pass-band ripple tuning controller32(1), which may be a self-contained automatic test equipment (ATE). The DAS RU30(1) comprises an electronically tunable equalizer34(1) coupled with a controller122. The DAS RU30(1) further comprises a DL processing unit124, a ceramic duplexer126, and an antenna port128. The ceramic duplexer126comprises a DL ceramic filter36(1) configured to pass a DL pass-band frequency signal and block a UL pass-band frequency signal. Hence on the DL path, the pass-band frequency signal38(1) will propagate through the electronically tunable equalizer34(1), the DL processing unit124, and the DL ceramic filter36(1) before arriving at the antenna port128. According to the embodiment, the electronically tunable equalizer34(1) receives the pass-band frequency signal38(1) from a RF signal generator (not shown) and generates a weighted pass-band frequency signal48(1). The DL ceramic filter36(1) receives the weighted pass-band frequency signal48(1) and generates a filtered pass-band frequency signal49(1), which can be received at the antenna port128.

With reference toFIG. 6, the RF pass-band ripple tuning controller32(1) comprises a pass-band ripple measurement unit130and a process controller132. In a non-limiting example, the pass-band ripple measurement unit130and the process controller132may be integrated into a single entity, which may be enabled by hardware, software, or combination of both. The pass-band ripple measurement unit130is coupled to the antenna port128and measures the pass-band ripple in the filtered pass-band frequency signal49(1). The process controller132is configured to receive a ripple measurement output134from the pass-band ripple measurement unit130and compare the pass-band ripple in the ripple measurement output134to a predefined ripple performance threshold. If the ripple is greater than the predefined pass-band ripple threshold, the process controller132is configured to generate a ripple tuning instruction136to the controller122. In another non-limiting example, the process controller132and the controller122may be integrated into the same entity. In response to receiving the ripple tuning instruction136, the controller122configures the electronically tunable equalizer34(1) to a first capacitance state among the plurality of capacitance states44(1)-44(N) by sending the capacitance state input46(1) to the electronically tunable equalizer34(1). The controller122is configured to repeatedly configure the electronically tunable equalizer34(1) to a next capacitance state among the plurality of capacitance states44(1)-44(N) until all of the plurality of capacitance states44(1)-44(N) are tested. For each of the plurality of capacitance state44(1)-44(N), a corresponding filtered pass-band frequency signal49(1) is generated by the wireless communication unit30(1) and received by the pass-band ripple measurement unit130via the antenna port128. The pass-band ripple measurement unit130measures the pass-band ripple in the filtered pass-band frequency signal49(1) and provides the pass-band ripple to the process controller132in the ripple measurement report134. After the controller122has configured the electronically tunable equalizer34(1) to all of the plurality of capacitance states44(1)-44(N), the process controller132is able to identify a desired pass-band ripple among all pass-band ripple measurements received from the pass-band ripple measurement unit130. The process controller132can then instruct the controller122to configure the electronically tunable equalizer34(1) to the capacitance state associated with the desired pass-band ripple for desired pass-band ripple performance in the DAS RU30(1).

With continuing reference toFIG. 6, the DAS RU30(1) further comprises a UL digital processing unit138coupled to a UL ceramic filter36(2) in the ceramic duplexer126. The UL ceramic filter36(2) is coupled to the antenna port128and configured to pass a UL pass-band frequency signal and block a DL pass-band frequency signal. By the UL ceramic filter36(2) receiving a UL pass-band frequency signal (not shown) from the antenna port128and providing the UL pass-band frequency signal (not shown) to the UL digital processing unit138, the exemplary RF pass-band ripple tuning system120can be configured to perform the RF pass-band ripple tuning process on a UL path of the DAS RU30(1).

To help explain how the electronically tunable equalizer34inFIG. 2is able to modify the equalizer response in the weighted pass-band frequency signal48inFIG. 2,FIG. 7is provided.FIG. 7is a schematic diagram of an exemplary electronically tunable equalizer34that can be configured to select a capacitance state among the plurality of capacitance states44(1)-44(N), causing the exemplary electronically tunable equalizer34to change the equalized response of the weighted pass-band frequency signal48. The electronically tunable equalizer34comprises a pass-band RF signal input140configured to receive the pass-band frequency signal38(2) and a pass-band RF signal output142configured to output the weighted pass-band frequency signal48(2). The electronically tunable equalizer34further comprises a first resonator42(1) and a second resonator42(2), both coupled to the pass-band RF signal input140and the pass-band RF signal output142. According to one embodiment of design, the first resonator42(1) comprises a capacitor C1and an inductor L1, the second resonator42(2) comprises a capacitor C2and an inductor L2. In a non-limiting example, the capacitor C1has a capacitance of 5.6 pF, the first inductor has an inductance of 8.2 nanohenry (nH), the second capacitor C2has a capacitance of 2.4 pF, and the second inductor has an inductance of 8.2 nH. Therefore, the first resonator42(1) and the second resonator42(2) are generating a first resonance frequency F1(not shown) and a second resonance frequency F2(not shown), respectively. A resonance frequency is a frequency of electrical oscillation determined by the physical parameters (e.g., capacitor C1, C2and inductor L1, L2) of the first resonator42(1) and the second resonator42(2), respectively. The first resonance frequency F1and the second resonance frequency F2are determined as F1=1/(2π√(L1·C1)) and F2=1/(2π√(L2·C2)), respectively. The first resonance frequency F1and the second resonance frequency F2are combined at the pass-band RF signal output142, thus generating the weighted pass-band frequency signal48(2). As long as the capacitance C1and the inductance L1remain constant in the first resonator42(1), the corresponding resonance frequency F1will not change. Same is true for the second resonance frequency F2generated by the second resonator42(2). As a result, the equalizer response of the weighted pass-band frequency48(2) is static for the pass-band frequency signal38(2).

With reference toFIG. 7, the electronically tunable equalizer34further comprises an electronically tunable capacitor circuit40(1) coupled in parallel to the capacitor C1in the first resonator42(1). The electronically tunable capacitor circuit40(1) comprises a capacitance state selector45(1), a plurality of capacitance states44(1)-44(N), and a tunable capacitor Cd. Each of the plurality of capacitance states44(1)-44(N) correspond to a specific capacitance of the tunable capacitor Cd. In another non-limiting example, the tunable capacitor Cd has a tunable capacitance range between 0.5 pF and 4.5 pF that is divided into thirty-two (32) frequency states separated by a capacitance step of 0.12 pF. The capacitance state selector45(1) configures the capacitor Cd to one of the plurality of capacitance states44(1)-44(N) based on the capacitance state input46(2). According to well established theorem, the capacitance is (C1+Cd) when the capacitor C1is coupled in parallel with the capacitor Cd. As result, the first resonator42(1) generates a modified first resonance frequency F1M(not shown) that can be expressed as F1M=1/[2π√(L1·(C1+Cd))]. In this regard, the modified first resonator frequency F1Mbecomes tunable by tuning the capacitor Cd among the plurality of capacitance state44(1)-44(N). As a non-limiting example, the modified first resonator frequency F1Mhas a tunable frequency range between 533 MHz and 712 MHz when capacitor Cd is tuned between 0.5 pF and 4.5 pF. The second resonance frequency F2is approximately fixed at 1134 MHz since it is largely not affected by the capacitor Cd in the electronically tunable capacitor circuit40(1). Further, the equalizer response of the weighted pass-band frequency signal48(2) also becomes tunable based on the plurality of capacitance states44(1)-44(N) because the weighted pass-band frequency signal48(2) is a dependent of the modified first resonance frequency F1Mand the second resonance frequency F2. With continuing reference toFIG. 7, the electronically tunable equalizer34further comprises an attenuator144coupled across the pass-band RF signal input140and the pass-band RF signal output142. The attenuator144is configured to work with the resonators42(1),42(2) to produce the weighted pass-band frequency signal48(2). To help illustrate how the plurality of capacitance states44(1)-44(N) in the electronically tunable capacitor circuit40(1) effect the equalizer response of the electronically tunable equalizer34,FIG. 8andFIG. 9are provided and discussed next. Elements ofFIG. 7are referenced in connection withFIG. 8andFIG. 9, and will not be re-described herein.

FIG. 8illustrates plots of different equalizer responses associated with a plurality of lower capacitance states of the electronically tunable capacitor circuit40(1) (shown inFIG. 7). The plots inFIG. 8correspond to the equalizer responses of the electronically tunable equalizer34at capacitance states zero (0), four (4), eight (8), and twelve (12), respectively. The distance between points m5and m6on the vertical axis represents the amount of pass-band ripple reduction, measured in dB, that can be achieved by the corresponding capacitance state between the related frequencies of points m5and m6. Take the plot of capacitance state twelve (12) as an example, the vertical distance between points m5and m6indicates that the electronically tunable equalizer34, when tuned to capacitance state twelve (12), is able to provide approximately 1.3 dB (approximately calculated as: negative 6.3 dB at m5minus negative 7.6 dB at m6) pass-band ripple reduction in the 862 MHz to 894 MHz pass-band frequency range. Plots of other capacitance states inFIG. 8can be interpreted according to the same principles as described for capacitance state twelve (12).

In this regard,FIG. 9illustrates exemplary plots of different equalizer responses associated with a plurality of upper capacitance states of the electronically tunable capacitor circuit40(1) (shown inFIG. 7). Taking the plot of capacitance state twenty-eight (28) as an example, the vertical distance between points m5and m6indicates that the electronically tunable equalizer34, when tuned to capacitance state twenty-eight (28), is able to provide approximately −0.4 dB pass-band ripple reduction in the 862 MHz to 894 MHz frequency range. Clearly, capacitance state twelve (12) provides a higher pass-band ripple reduction than capacitance state twenty-eight (28) in the 860 MHz to 900 MHz frequency range. The amount of the required ripple reduction and its location along the pass-band depend on the ripple of the ceramic filter that is equalized.

In this regard,FIG. 10is an exemplary plot of an overall frequency response of the electronically tunable equalizer34(1) inFIG. 6with an exemplary pass-band ripple equalization of approximately 3 dB in a pass-band frequency between 840 MHz and 940 MHz (−1.4 dB at 840 MHz to −4.4 dB at 940 MHz). Elements ofFIG. 6andFIG. 7are referenced in connection withFIG. 10and will not be re-described herein. As described earlier inFIG. 7, the equalizer response of the electronically tunable equalizer34is a combined result of the modified first resonator frequency F1mand the second resonator frequency F2. The modified first resonator frequency F1mis modified by the tunable capacitor Cd among the plurality of capacitance states44(1)-44(N) in the electronically tunable capacitor circuit40(1). Point m3represents the modified first resonator frequency, which is tunable between 533 MHz and 745 MHz according to the example inFIG. 7. The plotted curve148and point m4represent the second resonator frequency that is fixed at 1134 MHz according to the example inFIG. 7.

The DAS80inFIG. 5AandFIG. 5Bmay also be provided in an indoor environment, as illustrated inFIG. 11.FIG. 11is a partially schematic cut-away diagram of a building infrastructure150employing the DASs80described herein. The building infrastructure150in this embodiment includes a first (ground) floor152(1), a second floor152(2), and a third floor152(3). The floors152(1)-152(3) are serviced by the central unit154to provide the antenna coverage areas156in the building infrastructure150. The central unit154is communicatively coupled to the base station158to receive downlink communications signals160D from the base station158. The central unit154is communicatively coupled to the remote antenna units162to receive the uplink communications signals160U from the remote antenna units162, as previously discussed above. The downlink and uplink communications signals160D,160U communicated between the central unit154and the remote antenna units162are carried over a riser cable164. The riser cable164may be routed through interconnect units (ICUs)166(1)-166(3) dedicated to each floor152(1)-152(3) that route the downlink and uplink communications signals160D,160U to the remote antenna units162and also provide power to the remote antenna units162via array cables168.

FIG. 12is a schematic diagram representation of additional detail illustrating a computer system170that could be employed in a RF pass-band ripple tuning system, including as the RF pass-band ripple tuning controller32, the controller122, and the process controller132in the RF pass-band ripple tuning system28,120inFIGS. 2 and 7, respectively, to reduce pass-band ripple in RF filters used for pass-band filtering in a wireless communication unit32(“DAS unit”). The control system170is adapted to execute instructions from an exemplary computer-readable medium to perform these and/or any of the functions or processing described herein.

In this regard, the computer system170inFIG. 12may include a set of instructions that may be executed to calculate pass-band ripple of DAS unit in a DAS and instruct the DAS unit to initiate RF filter pass-band ripple reduction process. The computer system170may be connected (e.g., networked) to other machines in a LAN, an intranet, an extranet, or the Internet. While only a single device is illustrated, the term “device” shall also be taken to include any collection of devices that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. The computer system170may be a circuit or circuits included in an electronic board card, such as, a printed circuit board (PCB), a server, a personal computer, a desktop computer, a laptop computer, a personal digital assistant (PDA), a computing pad, a mobile device, or any other device, and may represent, for example, a server or a user's computer.

The exemplary computer system170in this embodiment includes a processing device or processor172, a main memory174(e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM), such as synchronous DRAM (SDRAM), etc.), and a static memory176(e.g., flash memory, static random access memory (SRAM), etc.), which may communicate with each other via a data bus178. Alternatively, the processor172may be connected to the main memory174and/or static memory176directly or via some other connectivity means. The processor172may be a controller, and the main memory174or static memory176may be any type of memory.

The processor172represents one or more general-purpose processing devices, such as a microprocessor, central processing unit, or the like. More particularly, the processor172may be a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing other instruction sets, or other processors implementing a combination of instruction sets. The processor172is configured to execute processing logic in instructions for performing the operations and steps discussed herein.

The computer system170may further include a network interface device180. The computer system170also may include an input182, configured to receive input and selections to be communicated to the computer system170when executing instructions. The computer system170also may include an output184, including but not limited to a display, a video display unit (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device (e.g., a keyboard), and/or a cursor control device (e.g., a mouse).

The system170may include a data storage device that includes instructions188stored in a computer-readable medium190. The instructions188may also reside, completely or at least partially, within the main memory174and/or within the processor172during execution thereof by the computer system170, the main memory174and the processor172also constituting computer-readable medium. The instructions188may further be transmitted or received over a network192via the network interface device200.

The embodiments disclosed herein include steps that may be performed by hardware components or may be embodied in machine-executable instructions, used to cause a processor programmed with the instructions to perform the steps. Alternatively, the steps may be performed by a combination of hardware and software.

The embodiments disclosed herein may be provided as a computer program product, or software, that may include a machine-readable medium (or computer-readable medium) having stored instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the embodiments disclosed herein.

Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred. Various modifications and variations can be made without departing from the spirit or scope of the invention. Since variations of the disclosed embodiments incorporating the spirit of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.