Programmable digital up-conversion for concurrent multi-band signals

Embodiments of a digital up-conversion system for a concurrent multi-band signal and methods of operation thereof are disclosed. In one embodiment, a digital up-conversion system includes multiple digital up-converter chains, each for a different frequency band of the concurrent multi-band signal, and a digital combiner that combines up-converted signals output by the digital up-converter chains to provide a combined digital signal. The combined digital signal is processed by one or more additional processing components including a digital-to-analog converter (DAC) to provide the concurrent multi-band signal.

FIELD OF THE DISCLOSURE

The present disclosure relates to digital up-conversion and more particularly digital up-conversion for a concurrent multi-band signal.

BACKGROUND

Traditionally, baseband to radio frequency (RF) up-conversion is performed in the analog domain with one of three types of architectures, namely, a heterodyne architecture, a super-heterodyne architecture, or a direct conversion architecture. Analog up-conversion architectures and previous attempts at digital up-conversion architectures have generally been frequency dependent in that they only operate over a small frequency band. In other words, a traditional analog up-converter that is designed for one frequency band will not operate effectively for a different frequency band. For example, an up-converter designed for operation at 800 megahertz (MHz) will not operate properly at 450 MHz, 1.5 GHz, or 1.9 gigahertz (GHz). Therefore, it is not possible for a radio designed for use in one frequency band to be converted for use in an alternate frequency band without physically replacing an up-converter in the radio with a newly designed up-converter for the alternate frequency band or having multiple up-converters each capable of operating in a different frequency band. Either option adds an increase to the cost of a system. Another disadvantage of an analog up-converter is that it is subject to issues related to analog variability such as, but not limited to, component to component variability, temperature variability, voltage variability, and variability due to aging.

A flexible, programmable digital up-conversion system that addresses the issues above is described in commonly owned and assigned U.S. Patent Application Publication No. 2010/0098191 A1, entitled METHODS AND SYSTEMS FOR PROGRAMMABLE DIGITAL UP-CONVERSION, filed on Oct. 20, 2008, and published on Apr. 22, 2010, which is hereby incorporated herein by reference in its entirety.

Further issues arise when up-converting for a concurrent multi-band signal. For instance, while the digital up-conversion system of U.S. Patent Application Publication No. 2010/0098191 A1 can be used for concurrent multi-band signals, it must treat the concurrent multi-band signal as a single wide-band signal. However, due to the large bandwidth of a concurrent multi-band signal, treating the concurrent multi-band signal as a single wide-band signal may exceed or approach processing capabilities of current Application Specific Integrated Circuit (ASIC) and Field Programmable Gate Array (FPGA) technology. Thus, there is a need for a digital up-conversion system for a concurrent multi-band signal that also addresses the other issues discussed above.

SUMMARY

Systems and methods are disclosed for digital up-conversion of a concurrent multi-band signal. As used herein, a “concurrent multi-band signal” is a signal that contains frequency components occupying multiple frequency bands (i.e., a first continuous frequency band, a second continuous frequency band, etc.) with no frequency components between adjacent frequency bands. In general, the systems and methods disclosed herein make use of complex tuning at baseband, up-sampling, and digital filtering to create a flexible digital up-conversion system for a concurrent multi-band signal.

In one embodiment, a digital up-conversion system for a concurrent multi-band signal includes multiple digital up-converter chains, each for a different frequency band of the concurrent multi-band signal, and a digital combiner that combines up-converted signals output by the digital up-converter chains to provide a combined digital signal. The combined digital signal is processed by one or more additional processing components including a digital-to-analog converter (DAC) to provide the concurrent multi-band signal.

In one embodiment, one or more parameters of the digital up-converter chains are configured based on an effective sampling rate of the DAC such that, after processing by the one or more additional processing components, complex digital baseband signals for the frequency bands of the concurrent multi-band signal are up-converted to desired carrier frequencies of the corresponding frequency bands of the concurrent multi-band signal. In another embodiment, the effective sampling rate of the DAC is configured based on one or more predefined parameters of the digital up-converter chains such that, after processing by the one or more additional processing components, complex digital baseband signals for the frequency bands of the concurrent multi-band signal are up-converted to desired carrier frequencies of the corresponding frequency bands of the concurrent multi-band signal.

In one embodiment, each digital up-converter chain includes one or more digital up-converter stages and a digital quadrature modulator. For each digital up-converter chain, the one or more digital up-converter stages of the digital up-converter chain process a complex baseband signal for the corresponding frequency band of the concurrent multi-band signal to produce an output signal that includes an image of the complex baseband signal centered at a desired output frequency for the one or more digital up-converter stages. The digital quadrature modulator then processes the output signal of the one or more digital up-converter stages to provide the up-converted signal output by the digital up-converter chain. In the frequency domain, the digital quadrature modulation of the output signal results in frequency translating, or frequency-shifting, the image of the complex baseband signal to a desired up-conversion frequency for the digital up-converter chain. The desired up-conversion frequencies for the digital up-converter chains are such that, after processing of the combined signal by the one or more additional processing components including the DAC, images of the complex baseband signals are centered at the desired carrier frequencies of the corresponding frequency bands of the concurrent multiband signal.

In another embodiment, each digital up-converter chain includes one or more digital up-converter stages. For each digital up-converter chain, the one or more digital up-converter stages of the digital up-converter chain process a complex baseband signal for the corresponding frequency band of the concurrent multi-band signal to produce the up-converted signal output by the digital up-converter chain such that the up-converted signal includes an image of the complex baseband signal centered at a desired up-conversion frequency for the digital up-converter chain. The desired up-conversion frequencies for the digital up-converter chains are such that, after processing of the combined signal by the one or more additional processing components including a digital quadrature modulator followed by the DAC, images of the complex baseband signals are centered at center frequencies of the corresponding frequency bands of the concurrent multiband signal.

Further, in one embodiment, each complex up-converter stage of each digital up-converter chain includes a complex baseband tuner followed by an up-sampler and an image selection filter. For each digital up-converter chain, a baseband tuning frequency of the complex baseband tuner and a tuning frequency of the image selection filter for at least one of the complex up-converter stages in the digital up-converter chain are selected based on the effective sampling rate of the DAC such that, after processing of the combined signal by the one or more additional processing components including the DAC, an image of the complex baseband signal input to the digital up-converter chain is centered at a desired carrier frequency of the corresponding frequency band of the concurrent multi-band signal. In another embodiment, one or more parameters of the one or more additional processing components (e.g., the effective sampling rate of the DAC) are configured based on predetermined tuning frequencies of the image selection filters in the digital up-converter chains, and subsequently baseband tuning frequencies of the complex baseband tuners are determined such that, after processing of the combined signal by the one or more additional processing components including the DAC, images of the complex baseband signals input to the digital up-converter chains are centered at desired carrier frequencies of the corresponding frequency bands of the concurrent multi-band signal.

DETAILED DESCRIPTION

FIG. 1illustrates a programmable concurrent multi-band digital up-conversion system10according to one embodiment of the present disclosure. In general, the digital up-conversion system10operates to digitally up-convert a number (M) of complex baseband digital signals (I1, Q1through IM, QM) to provide a concurrent multi-band signal (SMB). As used herein, a concurrent multi-band signal, such as the concurrent multi-band signal (SMB), is a signal that contains frequency components occupying multiple frequency bands (i.e., a first continuous frequency band, a second continuous frequency band, etc.) with no frequency components between adjacent frequency bands. These frequency bands are referred to herein as “frequency bands” of the concurrent multi-band signal. In one embodiment, the concurrent multi-band signal includes two frequency bands and, as such, is also referred to herein as a concurrent dual-band signal.

For each frequency band of the concurrent multi-band signal, a center frequency of the frequency band is referred to herein as a carrier frequency of the concurrent multi-band signal. As such, the concurrent multi-band signal as defined herein includes multiple carrier frequencies. Frequency differences between adjacent carrier frequencies of the concurrent multi-band signal are referred to herein as carrier frequency spacings. A ratio of the carrier frequency spacing over a maximum individual baseband bandwidth (i.e., the maximum individual baseband bandwidth is a maximum bandwidth among the baseband signals that correspond to the frequency bands of the concurrent multi-band signal) is high such that a distortion or predistortion surrounding each of the carrier frequencies also occupies disjoint frequency bands. Some examples of situations or applications where such concurrent multi-band signals are used include multi-standard systems where each standard occupies a different frequency band, systems that transmit signals for multiple standards simultaneously, and systems having concurrent transmissions in multiple frequency bands for the same standard.

The digital up-conversion system10includes M digital up-converter chains12-1through12-M, where again M is the number of frequency bands in the concurrent multi-band signal (SMB) and is greater than or equal to 2. The digital up-converter chains12-1through12-M may also be generally referred to herein collectively as digital up-converter chains12or individually as a digital up-converter chain12. Each of the digital up-converter chains12-1through12-M performs digital up-conversion for a different one of the frequency bands of the concurrent multi-band signal (SMB). More specifically, the digital up-converter chain12-1digitally up-converts the complex baseband digital signal (I1, Q1) for a first frequency band of the concurrent multi-band signal (SMB) to provide a corresponding up-converted digital signal (SUP—1). Likewise, the digital up-converter chain12-M digitally up-converts the complex baseband signal (IM, QM) for an Mth frequency band of the concurrent multi-band signal (SMB) to provide a corresponding up-converted digital signal (SUP—M).

The digital up-converter chains12-1through12-M include corresponding complex digital up-converter stages14-1through14-M (generally referred to herein collectively as complex digital up-converter stages14and individually as complex digital up-converter stage14) and corresponding digital quadrature modulators16-1through16-M (generally referred to herein collectively as digital quadrature modulators16and individually as a digital quadrature modulator16). In this embodiment, each of the digital up-converter chains12includes one complex digital up-converter stage14. However, as discussed below, one or more or even all of the digital up-converter chains12may include one or more additional complex digital up-converter stages.

As illustrated, the complex digital up-converter stages14-1through14-M include complex baseband tuners18-1through18-M, up-samplers20-1through20-M, and image selection filters22-1through22-M, respectively, which are also generally referred to herein as complex baseband tuners18, up-samplers20, and image selection filters22. Looking first at the complex digital up-converter stage14-1of the digital up-converter chain12-1, the complex baseband tuner18-1first performs a complex tuning of the complex baseband digital signal (I1, Q1) for the first frequency band of the concurrent multi-band signal (SMB). Preferably, a sampling rate of the complex baseband digital signal (I1, Q1) is fS/N. Alternatively, sampling rate conversion may be utilized to convert the sampling rate of the complex baseband digital signal (I1, Q1) to fS/N prior to complex baseband tuning. Note that if rate conversion is needed, the rate conversion may alternatively be performed elsewhere in the digital up-conversion system10prior to a digital-to-analog converter (DAC)26(e.g., subsequent to the complex baseband tuner18-1, subsequent to the up-sampler20-1, subsequent to the image selection filter22-1, subsequent to the digital quadrature modulator16-1, or prior to the DAC26).

As discussed below in detail, the complex baseband tuner18-1tunes the complex baseband digital signal (I1, Q1) to a baseband tuning frequency (fBBT—1) to thereby produce a complex tuned digital signal (IBBT—1, QBBT—1). In one embodiment, the baseband tuning frequency (fBBT—1) is programmable or otherwise selectable within a range of −fS/2N and fS/2N, as discussed below in detail, where fSis an effective sampling rate of the DAC26and N is an up-sampling rate of the up-sampler20-1. The complex baseband tuner18-1is preferably utilized to provide fine tuning to achieve the desired carrier frequency for the corresponding frequency band of the concurrent multi-band signal. A particular example of a complex baseband tuner is described in commonly owned and assigned U.S. Patent Application Publication No. 2009/0316838 A1, entitled CORDIC BASED COMPLEX TUNER WITH EXACT FREQEUNCY RESOLUTION, filed on Jun. 23, 2008 and published on Dec. 24, 2009, is hereby incorporated herein by reference in its entirety.

The up-sampler20-1up-samples the complex tuned digital signal (IBBT—1, QBBT—1) at an up-sampling rate N, where N≧2, to produce an up-sampled digital signal (IUS—1, QUS—1) having a sampling rate of fS. In the frequency domain, the up-sampled digital signal (IUS—1, QUS—1) includes N images of the complex tuned digital signal (IBBT—1, QBBT—1) equally spaced apart in the frequency range of 0 to fS, where fSis the effective sampling rate of the DAC26. The up-sampler20-1is preferably utilized to provide coarse tuning to achieve the desired carrier frequency for the corresponding frequency band of the concurrent multi-band signal. The image selection filter22-1filters the up-sampled digital signal (IUS—1, QUS—1) to select a desired one of the images of the complex tuned digital signal (IBBT—1, QBBT—1) and thereby provide a complex output signal of the complex digital up-converter stage14-1(IOUT—1, QOUT—1). More specifically, the image selection filter22-1is preferably programmable via one or more parameters (e.g., filter coefficients) such that a passband of the image selection filter22-1is centered at a desired filter tuning frequency (fFILTERTUNING—1). The filter tuning frequency (fFILTERTUNING—1) is selected such that the desired image of the complex tuned digital signal (IBBT—1, QBBT—1) falls within the passband of the image selection filter22-1.

The digital quadrature modulator16-1performs quadrature modulation on the complex output signal (IOUT—1, QOUT—1) to provide the up-converted digital signal (SUP—1) output by the digital up-converter chain12-1. In the frequency domain, quadrature modulation results in frequency translating, or frequency-shifting, the image of the complex tuned digital signal (IBBT—1, QBBT—1) in the complex output signal (IOUT—1, QOUT—1) by fQMOD, where fQMODis a modulation frequency of the digital quadrature modulator16-1, and converting the complex signal into a real signal. Note, however, that fQMODmay be any frequency including zero. In one preferred embodiment, fQMODis equal to ±fS/4. In another embodiment, fQMODis equal to zero in which case there is no frequency translation of the image of the complex tuned digital signal (IBBT—1, QBBT—1) in the complex output signal (IOUT—1, QOUT—1). It should be further noted that fQMOD=0 takes just the real component of the complex output, where the imaginary part may need to be previously inverted depending on the desired sign of the quadrature modulation. The frequency-translated image of the complex tuned digital signal (IBBT—1, QBBT—1) is centered at a desired up-conversion frequency for the digital up-converter chain12-1.

Similarly, regarding the complex digital up-converter stage14-M of the digital up-converter chain12-M, the complex baseband tuner18-M first performs a complex tuning of the complex baseband digital signal (IM, QM) for the Mth frequency band of the concurrent multi-band signal (SMB). Preferably, a sampling rate of the complex baseband digital signal (IM, QM) is fS/N. Alternatively, sampling rate conversion may be utilized to convert the sampling rate of the complex baseband digital signal (IM, QM) to fS/N prior to complex baseband tuning. Note that if rate conversion is needed, the rate conversion may alternatively be performed elsewhere in the digital up-conversion system10prior to the DAC26(e.g., subsequent to the complex baseband tuner18-M, subsequent to the up-sampler20-M, subsequent to the image selection filter22-M, subsequent to the digital quadrature modulator16-M, or prior to the DAC26).

As discussed below in detail, the complex baseband tuner18-M first performs a complex tuning of the complex baseband digital signal (IM, QM) for the Mth frequency band of the concurrent multi-band signal (SMB). As discussed below in detail, the complex baseband tuner18-M tunes the complex baseband digital signal (IM, QM) to a baseband tuning frequency (fBBT—M) to thereby produce a complex tuned digital signal (IBBT—M, QBBT—M). In one embodiment, the baseband tuning frequency (fBBT—M) is programmable or otherwise selectable within a range of −fS/2N and fS/2N, as discussed below in detail, where fSis the effective sampling rate of the DAC26and N is an up-sampling rate of the up-sampler20-M.

The up-sampler20-M up-samples the complex tuned digital signal (IBBT—M, QBBT—M) at an up-sampling rate N, where N≧2, to produce an up-sampled digital signal (IUS—M, QUS—M) having a sampling rate of fS. In the frequency domain, the up-sampled digital signal (IUS—M, QUS—M) includes N images of the complex tuned digital signal (IBBT—M, QBBT—M) equally spaced apart in the frequency range of 0 to fS, where fSis the effective sampling rate of the DAC26. The image selection filter22-M filters the up-sampled digital signal (IUS—M, QUS—M) to select a desired one of the images of the complex tuned digital signal (IBBT—M, QBBT—M) and thereby provide a complex output signal (IOUT—M, QOUT—M) of the complex digital up-converter stage14-M. More specifically, the image selection filter22-M is preferably programmable via one or more parameters (e.g., filter coefficients) such that a passband of the image selection filter22-M is centered at a desired filter tuning frequency (fFILTERTUNING—M). The filter tuning frequency (fFILTERTUNING—M) is selected such that the desired image of the complex tuned digital signal (IBBT—M, QBBT—M) falls within the passband of the image selection filter22-M.

The digital quadrature modulator16-M performs quadrature modulation on the complex output signal (IOUT—M, QOUT—M) to provide the up-converted digital signal (SUP—M) output by the digital up-converter chain12-M. In the frequency domain, quadrature modulation results in frequency translating, or frequency-shifting, the image of the complex tuned digital signal (IBBT—M, QBBT—M) in the complex output signal (IOUT—M, QOUT—M) by fQMOD, where fQMODis a modulation frequency of the digital quadrature modulator16-M, and converting the complex signal into a real signal. Again, fQMODcan be any desired frequency including zero. Note that the modulation frequencies of the digital quadrature modulators16may all be the same or, alternatively, one or more of the digital quadrature modulators16may have different modulation frequencies. The frequency-translated image of the complex tuned digital signal (IBBT—M, QBBT—M) is centered at a desired up-conversion frequency for the digital up-converter chain12-M.

Notably, the digital quadrature modulators16may be configurable to operate on a definition of quadrature modulation as a+jb or a−jb. This may be desirable because, for example, different cellular communication standards (e.g., Code Division Multiple Access (CDMA) 2000 and 3rdGeneration Partnership Project (3GPP)) may define quadrature modulation differently. Therefore, in order to accommodate different communication standards, the digital quadrature modulator16may be configurable in this manner. Alternatively, this configuration may be handled in the modem that generates the complex baseband digital signals (I1, Q1through IM, QM) by a complex conjugate function prior to the complex baseband tuners18-1through18-M that can be activated or deactivated as needed, or in the analog domain (i.e., after the DAC26) which is possible if there are two DACs26, namely, one DAC26for I and one DAC26for Q. Further, in one embodiment, the digital quadrature modulators16are combined with the corresponding image selection filters22.

For more information regarding some example implementations of the complex baseband tuners18, the up-samplers20, the image selection filters22, and the digital quadrature modulators16, the interested reader is directed to commonly owned and assigned U.S. Patent Application Publication No. 2010/0098191 A1, entitled METHODS AND SYSTEMS FOR PROGRAMMABLE DIGITAL UP-CONVERSION, filed on Oct. 20, 2008 and published on Apr. 22, 2010, which has been incorporated herein by reference in its entirety. For example, while the up-sampler20and the image selection filter22of each complex digital up-converter stage14may be implemented as separate components, they are not limited thereto. The up-sampler20and the image selection filter22may alternatively be implemented together as a polyphase filter that performs both up-sampling and image selection filtering.

The up-converted digital signals (SUP—1through SUP—M) are combined by a digital combiner24to provide a combined signal (SCOMB). The DAC26receives the combined signal (SCOMB) from the digital combiner24and converts the combined signal (SCOMB) to an analog signal (SDAC) at the effective sampling rate (fS) of the DAC26. Notably, as used herein, a “digital” signal is a discrete time signal, whereas an “analog” signal is a continuous time signal. Further, the term “effective” is used to define that the DAC26may receive a signal input having a sampling rate of fSor may receive multiple parallel inputs P, each with a sampling rate of fS/P, such that in combination the sampling rate processed by the DAC26is fS. Such parallel inputs may be carried by, for example, one or more higher rate serial links. When considering the frequency domain, digital-to-analog conversion by the DAC26also generates images of the spectrum occurring between DC and fSrepeatedly in the positive and negative frequency directions. More specifically, the spectrum of DC to fSis repeated in the positive direction between fSand 2fS, 2fSand 3fS, etc. and in the negative frequency direction between 0 and −fS, −fSand −2fS, −2fSand −3fS, etc.

In one embodiment, the effective sampling rate (fS) of the DAC26is predetermined and potentially fixed. However, in another embodiment, the effective sampling rate (fS) of the DAC26is configurable. In either case, the effective sampling rate (fS) of the DAC26is preferably sufficient to at least be able to convert the concurrent multi-band signal (SMB) plus a separation bandwidth between a first frequency band of the concurrent multi-band signal (SMB) and a second frequency band of the concurrent multi-band signal (SMB).

The DAC26may be operated in a baseband mode (or more generically a sinc mode) if it is desired to up-convert the signal to a location in the first Nyquist zone (i.e., frequency from DC to fS/2). A DAC operated in the baseband mode has a frequency response that produces a useful output in the first Nyquist zone. If the DAC26supports a radio frequency (RF) mode (or more generically a modified sinc mode), then the DAC26can be used to up-convert the signal in the second Nyquist zone (i.e., frequency from fS/2 to fS), the third Nyquist zone (i.e., frequency from fSto 3fS/2), or possibly the fourth or higher Nyquist zone. In some embodiments, a DAC that supports an RF mode can do so due to a configurable output stage adapted to modify the frequency response of the DAC in the second and third Nyquist zones and/or higher Nyquist zones to be amenable to operation in these zones. The zone that is targeted will depend on one or more factors, such as, but not limited to, the desired up-conversion frequencies for the frequency bands of the concurrent multi-band signal (SMB), the maximum sampling rate of the DAC26, the performance capabilities of the DAC26, and the overall desired performance of the digital up-conversion system10.

An RF filter28filters the analog signal (SDAC) from the DAC26to provide the concurrent multi-band signal (SMB). More specifically, the RF filter28passes the images of the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) centered at the desired carrier frequencies of the frequency bands of the concurrent multi-band signal (SMB) while attenuating, or removing, the remaining undesired images and frequency-flipped images of the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M). For each frequency band of the concurrent multi-band signal (SMB), the desired image may be below the sampling rate fSof the DAC26(e.g., in the first or second Nyquist zones) or above the sampling rate fSof the DAC26(e.g., in the third or higher Nyquist zone). The RF filter28may be implemented as a single concurrent multi-band filter or, alternatively, the RF filter28may be implemented as a number of parallel filters. More specifically, in one particular embodiment, a splitter provides the analog signal (SDAC) to each of M parallel filters, each configured to provide filtering for a corresponding frequency band of the concurrent multi-band signal (SMB). The resulting filtered signals are then combined to provide the concurrent multi-band signal (SMB).

Before proceeding, it should be noted that, while not illustrated, other components (e.g., rate change filter(s)) may be included in the digital up-converter chains12and/or in the combined chain (i.e., the components after the digital combiner24). Further, in some embodiments, the various components may be in a different order than that illustrated inFIG. 1. For example, in an alternative embodiment, the digital quadrature modulators16may be placed between the complex baseband tuners18and the up-samplers20. Also, in some embodiments, some or all of the components of the digital up-conversion system10are implemented using one or more Field Programmable Gate Arrays (FPGAs), one or more Application Specific Integrated Circuits (ASICs), or the like, or any combination thereof.

As discussed below, in one embodiment, the baseband tuning frequencies (fBBT—1through fBBT—M) and the filter tuning frequencies (fFILTERTUNING—1through fFILTERTUNING—M) are selected based on a predetermined and potentially fixed effective sampling rate (fS) of the DAC26such that the complex baseband digital signals (I1, Q1through IM, QM) are up-converted to the desired carrier frequencies of the concurrent multi-band signal (SMB). More specifically, the baseband tuning frequencies (fBBT—1through fBBT—M) and the filter tuning frequencies (fFILTERTUNING—1through fFILTERTUNING—M) are selected such that images of the complex baseband digital signals (I1, Q1through IM, QM) in the up-converted digital signals (SUP—1through SUP—M) are located at desired up-conversion frequencies. The desired up-conversion frequencies are such that, after further processing of the combined signal (SCOMB) by the digital combiner24, the DAC26, and the RF filter28, images of the complex baseband digital signals (I1, Q1through IM, QM) are located at the desired carrier frequencies of the corresponding frequency bands of the concurrent multi-band signal (SMB). Alternatively, the effective sampling rate (fS) of the DAC26may be configurable and selected based on predetermined values for the filter tuning frequencies (fFILTERTUNING—1through fFILTERTUNING—M) and subsequently the baseband tuning frequencies (fBBT—1through fBBT—M) are determined such that, after processing of the combined signal (SCOMB) by the digital combiner24, the DAC26, and the RF filter28, images of the complex baseband digital signals (I1, Q1through IM, QM) are located at the desired carrier frequencies of the corresponding frequency bands of the concurrent multi-band signal (SMB).

FIGS. 2A through 2Mare frequency-domain diagrams that graphically illustrate the operation of the digital up-conversion system10ofFIG. 1for one example where the concurrent multi-band signal (SMB) is a concurrent dual-band signal.FIGS. 2A through 2Eillustrate the operation of the digital up-converter chain12-1for the first band of the concurrent dual-band signal. As illustrated inFIG. 2A, the complex baseband digital signal (I1, Q1) is centered at DC. The complex baseband tuner18-1tunes the complex baseband digital signal (I1, Q1) to the baseband tuning frequency (fBBT—1), as illustrated inFIG. 2B. After up-sampling by the up-sampler20-1, the up-sampled digital signal (IUS—1, QUS—1) includes N equally spaced images of the complex tuned digital signal (IBBT—1, QBBT—1) between DC and fS, wherein in this example N=8, as illustrated inFIG. 2C. The image selection filter22-1then filters the up-sampled digital signal (IUS—1, QUS—1) to select the desired image, as illustrated inFIG. 2D. Finally, after digital quadrature modulation, the image in the complex output signal (IOUT—1, QOUT—1) from the image selection filter22-1is frequency translated by a frequency of fQMOD, to provide the up-converted digital signal (SUP—1), as illustrated inFIG. 2E. In addition, because the up-converted digital signal (SUP—1) is a real signal, it also includes frequency-flipped images of frequency-translated images.

FIGS. 2F through 2Jillustrate the operation of the digital up-converter chain12-M for the Mth band of the concurrent dual-band signal where for the concurrent dual-band signal M=2. As illustrated inFIG. 2F, the complex baseband digital signal (I2, Q2) is centered at DC. The complex baseband tuner18-2tunes the complex baseband digital signal (I2, Q2) to the baseband tuning frequency (fBBT—2), as illustrated inFIG. 2G. After up-sampling by the up-sampler20-2, the up-sampled digital signal (IUS—2, QUS—2) includes N equally spaced images of the complex tuned digital signal (IBBT—2, QBBT—2) between DC and fS, wherein in this example N=8, as illustrated inFIG. 2H. The image selection filter22-2then filters the up-sampled digital signal (IUS—2, QUS—2) to select the desired image, as illustrated inFIG. 2I. Finally, after digital quadrature modulation, the image in the complex output signal (IOUT—2, QOUT—2) from the image selection filter22-2is frequency translated by a frequency of fQMODto provide the up-converted digital signal (SUP—2), as illustrated inFIG. 2J. In addition, because the up-converted digital signal (SUP—2) is a real signal, it also includes frequency-flipped images of frequency-translated images.

Then, as illustrated inFIG. 2K, the digital combiner24combines the up-converted digital signals (SUP—1and SUP—2) to provide the combined signal (SCOMB). Next, the combined signal (SCOMB) is digital-to-analog converted by the DAC26to provide the analog signal (SDAC) as illustrated inFIG. 2L. As shown, the analog signal (SDAC) includes images of the spectrum occurring between DC and fSrepeatedly in the positive frequency direction. While not shown, the images of the spectrum also occur repeatedly in the negative frequency direction. Lastly, the RF filter28selects images located at center frequencies (fC1and fC2) of the frequency bands of the concurrent dual-band signal to thereby provide the concurrent dual-band signal, as illustrated inFIG. 2M. Thus, by using complex baseband tuning, up-sampling, image selection filtering, and quadrature modulation, images of the complex baseband digital signals (I1, Q1and I2, Q2) are produced at the desired carrier frequencies of the concurrent dual-band signal.

FIG. 3illustrates the digital up-conversion system10according to another embodiment of the present disclosure. As illustrated, the digital up-conversion system10is substantially the same as that ofFIG. 1. However, in this embodiment, at least some of the digital up-converter chains12-1through12-M include multiple complex digital up-converter stages. More specifically, in this example, the digital up-converter chain12-1includes the complex digital up-converter stage14-1as well as one or more additional complex digital up-converter stages30-1. The additional complex digital converter stage(s)30-1may be implemented like the complex digital up-converter stage14-1ofFIG. 1. However, in this embodiment, up-sampling by the desired factor of N is split between the up-samplers of the complex digital up-converter stages14-1and30-1.

In one embodiment, the baseband tuning frequencies and filter tuning frequencies of the complex baseband tuners and image selection filters of the complex digital up-converter stages14-1and30-1are determined based on the effective sampling rate (fS) of the DAC26and the collective up-sampling rate (N) of the up-samplers such that the up-converted digital signal (SUP—1) includes an image of the complex baseband digital signal (I1, Q1) at the desired up-conversion frequency for the first frequency band of the concurrent multi-band signal (SMB). Alternatively, the filter tuning frequencies of the image selection filters of the complex digital up-converter stages14-1and30-1are predetermined, and the effective sampling rate (fS) of the DAC26and subsequently the baseband tuning frequencies of the complex baseband tuners are configured such that, after further processing of the combined signal (SCOMB) by the DAC26and the RF filter28, an image of the complex baseband digital signal (I1, Q1) is centered at the desired carrier frequency for the first frequency band of the concurrent multi-band signal (SMB).

Likewise, the digital up-converter chain12-M includes the complex digital up-converter stage14-M as well as one or more additional complex digital up-converter stages30-M. The additional complex digital converter stage(s)30-M may be implemented like the complex digital up-converter stage14-M ofFIG. 1. However, in this embodiment, up-sampling by the desired factor of N is split between the up-samplers of the complex digital up-converter stages14-M and30-M.

In one embodiment, the baseband tuning frequencies and filter tuning frequencies of the complex baseband tuners and image selection filters of the complex digital up-converter stages14-M and30-M are determined based on the effective sampling rate (fS) of the DAC26and the collective up-sampling rate (N) of the up-samplers such that the up-converted digital signal (SUP—M) includes an image of the complex baseband digital signal (IM, QM) at the desired up-conversion frequency for the Mth frequency band of the concurrent multi-band signal (SMB). Alternatively, the filter tuning frequencies of the image selection filters of the complex digital up-converter stages14-M and30-M are predetermined, and the effective sampling rate (fS) of the DAC26and subsequently the baseband tuning frequencies of the complex bandband tuners are configured such that, after further processing of the combined signal (SCOMB) by the DAC26and the RF filter28, an image of the complex baseband digital signal (IM, QM) is centered at the desired carrier frequency for the corresponding frequency band of the concurrent multi-band signal (SMB).

FIG. 4is a flow chart that illustrates the operation of the digital up-conversion system10ofFIGS. 1 and 3according to one embodiment of the present disclosure. First, the complex baseband tuners18-1through18-M complex tune the complex baseband digital signals (I1, Q1through IM, QM) to produce the corresponding complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) (step100). Next, the up-samplers20-1through20-M up-sample the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) to produce the up-sampled digital signals (IUS—1, QUS—1through IUS—M, QUS—M) (step102). The image selection filters22-1through22-M then select the desired images in the up-sampled digital signals (IUS—1, QUS—1through IUS—M, QUS—M) to produce the complex output signals (IOUT—1, QOUT—1through IOUT—M, QOUT—M) (step104). Note that if there are additional complex digital up-converter stages30-1through30-M as in the embodiment ofFIG. 3, then steps100through104are repeated for each of the additional complex digital up-converter stages30-1through30-M.

The digital quadrature modulators16then perform quadrature modulation on the complex output signals (IOUT—1, QOUT—1through IOUT—M, QOUT—M) output by the complex digital up-converter stages14-1/30-1through14-M/30-M to provide the up-converted digital signals (SUP—1through SUP—M) (step106). The digital combiner24then combines the up-converted digital signals (SUP—1through SUP—M) to provide the combined signal (SCOMB) (step108). The DAC26performs digital-to-analog conversion of the combined signal (SCOMB) to produce the analog signal (SDAC) (step110). Lastly, the analog signal (SDAC) is filtered to provide the concurrent multi-band signal (SMB) (step112).

Additional method steps may also involve determining the amount of complex tuning for the complex tuning step and determining filter coefficients used in the image selection filtering step. In some embodiments, an amount of complex tuning used in the complex tuning step and filter coefficients used in the image selection filtering step are each determined as a function of a predetermined and potentially fixed effective sampling rate (fS) of the DAC26such that the up-converted digital signals (SUP—1through SUP—M) include images of the complex baseband digital signals (I1, Q1through IM, QM) centered at the desired up-conversion frequencies and, after digital-to-analog conversion and RF filtering of the combined signal (SCOMB), images of the complex baseband digital signals (I1, Q1through IM, QM) are located at the desired carrier frequencies of the corresponding frequency bands of the concurrent multi-band signal (SMB).

If the sampling rate of the complex baseband digital signals (I1, Q1through IM, QM) is not fS/N, then re-sampling may be performed at some point during the method to ensure that the signal input to the DAC26has an effective sample rate of fS. If the sample rate of the complex baseband digital signals (I1, Q1through IM, QM) is not fS/N, then there may not be N images in the bandwidth between DC and fSas described in the example above. Rather, N images would occur between DC and the sample rate of the complex baseband digital signals (I1, Q1through IM, QM) multiplied by N.

In some embodiments, up-sampling and image selection filtering are implemented together as a polyphase filtering process. In some embodiments, quadrature modulation is implemented subsequent to, and in combination with, the polyphase filtering process.

In some embodiments, the steps described above for performing up-conversion may not be implemented in the particular order described and illustrated inFIG. 4. In some embodiments, digital quadrature modulation may be implemented subsequent to the complex baseband tuning of step100and prior to the up-sampling of step102.

As a result of the unique usage of complex tuning, the inherently repetitive nature of sampled signals, and programmable digital filtering, some embodiments of the method provide flexible digital up-conversion capable of tunability over a wide frequency range. Having such a wide frequency range of tunability, the method may be used for effectively re-banding a radio from one set of concurrent frequency bands to another set of concurrent frequency bands in a manner that is not possible with conventional analog radios. Whereas conventional analog radios would typically need to be redesigned for different sets of concurrent frequency bands, a radio implementing some embodiments of the digital up-conversion system10disclosed herein can be easily reconfigured by providing the radio with information to change the operating parameters of one or more programmable components such that when the operating parameters are implemented the radio operates in the new set of frequency bands. The method may be used to reconfigure a radio which has been operating to provide a concurrent multi-band signal using one set of frequency bands to operate to provide a concurrent multi-band signal using a different set of frequency bands without significant redesign of the components performing the up-conversion function.

FIG. 5illustrates a process for configuring the digital up-conversion system10according to one embodiment of the present disclosure. In this particular embodiment, the digital up-converter chains12-1through12-M of the digital up-conversion system10are those ofFIG. 1. However, this process may be extended to configure the digital up-converter chains12-1through12-M having multiple complex digital up-converter stages as shown inFIG. 3. First, a highest carrier frequency (fCH) and/or a lowest carrier frequency (fCL) of the carrier frequencies of the concurrent multi-band signal are determined (step200). Next, the effective sampling rate (fS) of the DAC26is selected based on the highest carrier frequency (fCH) and/or the lowest carrier frequency (fCL) of the carrier frequencies of the concurrent multi-band signal (step202). More specifically, in one embodiment, the effective sampling rate (fS) is selected such that fS/2<fCL. In another embodiment, the effective sampling rate (fS) is selected such that fCH<fS. Note that while in this embodiment the highest carrier frequency (fCH) and/or the lowest carrier frequency (fCL) of the carrier frequencies of the concurrent multi-band signal are determined prior to selecting the effective sampling rate (fS) of the DAC26, the present disclosure is not limited thereto. In another embodiment, the effective sampling rate (fS) of the DAC26is selected first. Then, carrier frequencies that are suitable for the digital up-conversion system10are determined based on the selected effective sampling rate (fS) of the DAC26.

Next, the filter tuning frequencies (fFILTERTUNING—1through fFILTERTUNING—M) are determined for the image selection filters22-1through22-M based on the effective sampling rate (fS) of the DAC26(step204). In one embodiment, step202is performed such that the effective sampling rate (fS) of the DAC26is predetermined and fixed. In another embodiment, the effective sampling rate (fS) of the DAC26is configurable. The filter tuning frequencies (fFILTERTUNING—1through fFILTERTUNING—M) are such that the images of the complex baseband digital signals (I1, Q1through IM, QM), and more specifically the complex baseband digital signals (I1, Q1through IM, QM), produced at the desired up-conversion frequencies for the up-converted digital signals (SUP—1through SUP—M) are selected or, in other words, passed by the image selection filters22-1through22-M while the remaining images are attenuated, or removed.

Lastly, the baseband tuning frequencies (fBBT—1through fBBT—M) of the complex baseband tuners18-1through18-M are determined based on the effective sampling rate (fS) of the DAC26(step206). Again, in one embodiment, step202is performed such that the effective sampling rate (fS) of the DAC26is predetermined and fixed. In another embodiment, the effective sampling rate (fS) of the DAC26is configurable. In general, the baseband tuning frequencies (fBBT—1through fBBT—M) are select frequencies in the range of −fS/2N to fS/2N such that images of the complex baseband digital signals (I1, Q1through IM, QM) and more specifically images of the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) are produced at the desired up-conversion frequencies for the up-converted digital signals (SUP—1through SUP—M). The desired up-conversion frequencies for the up-converted digital signals (SUP—1through SUP—M) are such that, after digital-to-analog conversion and RF filtering, images of the complex baseband digital signals (I1, Q1through IM, QM) are located at the carrier frequencies of the corresponding frequency bands of the concurrent multi-band signal (SMB).

In one particular embodiment, for each frequency band X of the concurrent multi-band signal (SMB), the baseband tuning frequency (fBBT—X) and the filter tuning frequency (fFILTERTUNING—X) are determined as:

Once the baseband tuning frequencies (fBBT—1through fBBT—M) and the filter tuning frequencies (fFILTERTUNING—1through fFILTERTUNING—M) are determined, the complex baseband tuners18-1through18-M and the image selection filters22-1through22-M are configured accordingly (step208). The image selection filters22-1through22-M may be configured by, for example, providing corresponding filter coefficients to the image selection filters22-1through22-M. The process ofFIG. 5can be used perform a one-time configuration (e.g., during manufacturing). However, the process ofFIG. 5is preferably used to dynamically re-configure the digital up-conversion system10to accommodate different concurrent multi-band signals (i.e., concurrent multi-band signals having different frequency bands).

FIG. 6illustrates the digital up-conversion system10according to another embodiment of the present disclosure. In this embodiment, the digital up-conversion system10further includes a combined up-converter32that operates to provide additional up-conversion by a frequency (fCOMB) subsequent to the combining of the up-converted digital signals (SUP—1through SUP—M). In this embodiment, the up-conversion frequencies of the digital up-converter chains12are intermediate frequencies that provide sufficient frequency separation, and the combined up-converter32up-converts the combined signal (SCOMB) to produce an up-converted combined signal (SUP—COMB).

FIGS. 7 through 11illustrate embodiments that are similar to those ofFIGS. 1 through 6. However, in the embodiments ofFIGS. 7 through 11, digital quadrature modulation is performed subsequent to, rather than prior to, digitally combining the up-converted digital signals output by the digital up-converter chains12-1through12-M. More specifically,FIG. 7illustrates a programmable concurrent multi-band digital up-conversion system10according to another embodiment of the present disclosure. This embodiment is substantially the same as that ofFIG. 1. However, in this embodiment, the digital up-converter chains12do not include the digital quadrature modulators16. Instead, the digital up-conversion system10includes a digital quadrature modulator34that performs digital quadrature modulation after digitally combining complex outputs of the digital up-converter chains12.

More specifically, as discussed above, the digital up-conversion system10includes the M digital up-converter chains12-1through12-M, where again M is the number of frequency bands in the concurrent multi-band signal (SMB). Each of the digital up-converter chains12-1through12-M performs digital up-conversion for a different one of the frequency bands of the concurrent multi-band signal (SMB). In this embodiment, the digital up-converter chain12-1digitally up-converts the complex baseband digital signal (I1, Q1) for a first frequency band of the concurrent multi-band signal (SMB) to provide a corresponding complex up-converted digital signal (IUP—1, QUP—1). Likewise, the digital up-converter chain12-M digitally up-converts the complex baseband digital signal (IM, QM) for an Mth frequency band of the concurrent multi-band signal (SMB) to provide a corresponding complex up-converted digital signal (IUP—M, QUP—M).

The digital up-converter chains12-1through12-M include the complex digital up-converter stages14-1through14-M, respectively. In this embodiment, each of the digital up-converter chains12includes one complex digital up-converter stage14. However, as discussed below, one or more or even all of the digital up-converter chains12may also include one or more additional complex digital up-converter stages. As illustrated, the complex digital up-converter stages14-1through14-M include the complex baseband tuners18-1through18-M, the up-samplers20-1through20-M, and the image selection filters22-1through22-M, respectively, as discussed above. However, unlike the embodiment ofFIG. 1, the digital up-converter chains12-1through12-M do not include the digital quadrature modulators16-1through16-M. In this embodiment, the complex output signals output by the image selection filters22-1through22-M are referred to as complex up-converted digital signals (IUP—1, QUP—1through IUP—M, QUP—M) output by the digital up-converter chains12-1through12-M.

The complex up-converted digital signals (IUP—1, QUP—1through IUP—M, QUP—M) are combined by a complex digital combiner36to provide a complex combined signal (ICOMB, QCOMB). More specifically, the complex digital combiner36includes a first digital combiner38that combines, or sums, in-phase components (IUP—1through IUP—M) of the complex up-converted digital signals (IUP—1, QUP—1through IUP—M, QUP—M) to provide an in-phase component (ICOMB) of the complex combined signal (ICOMB, QCOMB). The complex digital combiner36also includes a second digital combiner40that combines, or sums, quadrature-phase components (QUP—1through QUP—M) of the complex up-converted digital signals (IUP—1, QUP—1through IUP—M, QUP—M) to provide a quadrature-phase component (QCOMB) of the complex combined signal (ICOMB, QCOMB).

The digital quadrature modulator34then performs quadrature modulation on the complex combined signal (ICOMB, QCOMB) to provide a quadrature modulated signal (SQMOD). In the frequency domain, quadrature modulation results in frequency translating, or frequency-shifting, the desired images of the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) in the combined complex signal (ICOMB, QCOMB) by fQMOD, where fQMODis a modulation frequency of the digital quadrature modulator34, and converting the complex signal into a real signal. Again, fQMODcan be any desired frequency including zero. Because the quadrature modulated signal (SQMOD) is a real signal, the quadrature modulated signal (SQMOD) includes both the frequency-translated images of the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) from the complex combined signal (ICOMB, QCOMB) and frequency-flipped images of the frequency-translated images. Before proceeding, it should be noted that, in an alternative embodiment, the quadrature modulator34may be an analog quadrature modulator that follows the DAC26and is prior to the RF filter28, in which case there would be two DACs26, namely, one DAC26for I and another DAC26for Q.

The DAC26receives the quadrature modulated signal (SQMOD) from the digital quadrature modulator34and converts it to the analog signal (SDAC). When considering the frequency domain, digital-to-analog conversion by the DAC26also generates images of the spectrum occurring between DC and fSrepeatedly in the positive and negative frequency directions. More specifically, the spectrum of DC to fSis repeated in the positive direction between fSand 2fS, 2fSand 3fS, etc. and in the negative frequency direction between 0 and −fS, −fSand −2fS, −2fSand −3fS, etc.

The RF filter28filters the analog signal (SDAC) from the DAC26to provide the concurrent multi-band signal (SMB). More specifically, the RF filter28passes the images of the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) in the digital-to-analog converted quadrature modulated signal (SMOD) centered at the desired carrier frequencies of the frequency bands of the concurrent multi-band signal (SMB) while attenuating, or removing, the remaining undesired images and frequency-flipped images of the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M). For each frequency band of the concurrent multi-band signal (SMB), the desired image may be below the sampling rate fSof the DAC26(e.g., in the first or second Nyquist zones) or above the sampling rate fS(e.g., in the third or higher Nyquist zone).

FIGS. 8A through 8Lare frequency-domain diagrams that graphically illustrate the operation of the digital up-conversion system10for one example where the concurrent multi-band signal (SMB) is a concurrent dual-band signal.FIGS. 8A through 8Dillustrate the operation of the digital up-converter chain12-1for the first band of the concurrent dual-band signal. As illustrated inFIG. 8A, the complex baseband digital signal (I1, Q1) is centered at DC. The complex baseband tuner18-1tunes the complex baseband digital signal (I1, Q1) to the baseband tuning frequency (fBBT—1), as illustrated inFIG. 8B. After up-sampling by the up-sampler20-1, the up-sampled digital signal (IUS—1, QUS—1) includes N equally spaced images of the complex tuned digital signal (IBBT—1, QBBT—1) between DC and fS, wherein in this example N=8, as illustrated inFIG. 8C. The image selection filter22-1then filters the up-sampled digital signal (IUS—1, QUS—1) to select the desired image and thereby provide the complex up-converted digital signal (IUP—1, QUP—1), as illustrated inFIG. 8D.

FIGS. 8E through 8Hillustrate the operation of the digital up-converter chain12-M for the Mth band of the concurrent dual-band signal where for the concurrent dual-band signal M=2. As illustrated inFIG. 8E, the complex baseband digital signal (I2, Q2) is centered at DC. The complex baseband tuner18-2tunes the complex baseband digital signal (I2, Q2) to the baseband tuning frequency (fBBT—2), as illustrated inFIG. 8F. After up-sampling by the up-sampler20-2, the up-sampled digital signal (IUS—2, QUS—2) includes N equally spaced images of the complex tuned digital signal (IBBT—2, QBBT—2) between DC and fS, wherein in this example N=8, as illustrated inFIG. 8G. The image selection filter22-2then filters the up-sampled digital signal (IUS—2, QUS—2) to select the desired image and thereby provide the complex up-converted digital signal (IUP—2, QUP—2), as illustrated inFIG. 8H.

Then, as illustrated inFIG. 8I, the complex digital combiner36combines the up-converted complex digital signals (IUP—1, QUP—1and IUP—2, QUP—2) to provide the complex combined signal (ICOMB, QCOMB). The complex combined signal (ICOMB, QCOMB) is quadrature modulated by the digital quadrature modulator34to provide the quadrature modulated signal (SQMOD), as illustrated inFIG. 8J. As shown inFIG. 8J, as a result of the quadrature modulation, the images in the complex combined signal (ICOMB, QCOMB) are frequency translated by a frequency fQMOD. In addition, because the quadrature modulated signal (SQMOD) is a real signal, it also includes frequency-flipped images of frequency-translated images.

Next, the quadrature modulated signal (SQMOD) is digital-to-analog converted by the DAC26to provide the analog signal (SDAC) as illustrated inFIG. 8K. As shown, the analog signal (SDAC) includes images of the spectrum occurring between DC and fSrepeatedly in the positive frequency direction. While not shown, the images of the spectrum also occur repeatedly in the negative frequency direction. Lastly, the RF filter28selects images located at carrier frequencies (fC1and fC2) of the frequency bands of the concurrent dual-band signal to thereby provide the concurrent dual-band signal, as illustrated inFIG. 8L. The RF filter28can be either a multi-band filter or a wide-band filter. Multi-Nyquist zone operation is possible if the RF filter28passes the desired signal in different Nyquist zones. Thus, in order to allow filtering, the image from one Nyquist zone should not land on or near the desired signal in another Nyquist zone. For example, if it is desired to transmit 728-746 MHz simultaneously with 2110-2170 MHz, then fS=2877 MHz does not work because the images land on each other, but fS=2500 MHz does work as the images are 330-390 MHz and 1745-1781 MHz which are both away from the desired frequencies. By using complex baseband tuning, up-sampling, image selection filtering, and quadrature modulation, images of the complex baseband digital signals (I1, Q1and I2, Q2) are produced at the desired carrier frequencies of the concurrent dual-band signal.

FIG. 9illustrates the digital up-conversion system10according to another embodiment of the present disclosure. As illustrated, the digital up-conversion system10is substantially the same as that ofFIG. 7. However, in this embodiment, at least some of the digital up-converter chains12-1through12-M include multiple complex digital up-converter stages30-1through30-M, as described above with respect toFIG. 3.

FIG. 10is a flow chart that illustrates the operation of the digital up-conversion system10ofFIGS. 7 and 9according to one embodiment of the present disclosure. This embodiment is substantially the same as that ofFIG. 4but where digital quadrature modulation has been moved after digitally combining the up-converted signals output by the digital up-converter chains12-1through12-M. First, the complex baseband tuners18-1through18-M tune the complex baseband digital signals (I1, Q1through IM, QM) to produce the corresponding complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) (step300). Next, the up-samplers20-1through20-M up-sample the complex tuned digital signals (IBBT—1, QBBT—1through IBBT—M, QBBT—M) to produce the up-sampled digital signals (IUS—1, QUS—1through IUS—M, QUS—M) (step302). The image selection filters22-1through22-M then select the desired images in the up-sampled digital signals (IUS—1, QUS—1through IUS—M, QUS—M) to thereby provide the complex up-converted digital signals (IUP—1, QUP—1through IUP—M, QUP—M) (step304). Note that if there are additional complex digital up-converter stages30-1through30-M as in the embodiment ofFIG. 9, then steps400through404are repeated for each of the additional complex digital up-converter stages30-1through30-M.

The complex digital combiner36then combines the complex up-converted digital signals (IUP—1, QUP—1through IUP—M, QUP—M) to provide the complex combined signal (ICOMB, QCOMB) (step306). The complex combined signal (ICOMB, QCOMB) is quadrature modulated to provide the quadrature modulated signal (SQMOD) (step308). The DAC26performs digital-to-analog conversion of the quadrature modulated signal (SQMOD) to produce the analog signal (SDAC) (step310). Lastly, the analog signal (SDAC) is filtered to provide the concurrent multi-band signal (SMB) (step312).

Notably, in one embodiment, the digital up-converter chains12-1through12-M in the embodiments ofFIGS. 7 and 9are configured based on a fixed or predetermined effective sampling rate (fS) of the DAC26using the process ofFIG. 5in order to provide the concurrent multi-band signal (SMB) with the desired carrier frequencies. In another embodiment, the effective sampling rate (fS) of the DAC26is configured based on predetermined parameters (e.g., complex tuning frequencies of the complex baseband tuners18and/or tuning frequencies of the image selection filters22) in order to provide the concurrent multi-band signal (SMB) with the desired carrier frequencies.

FIG. 11illustrates the digital up-conversion system10according to another embodiment of the present disclosure. In this embodiment, the digital up-conversion system10is a variation of the embodiments ofFIGS. 7 and 9wherein the digital up-conversion system10further includes the combined up-converter32as discussed above with respect toFIG. 6. The combined up-converter32operates to provide additional up-conversion by a frequency (fCOMB) subsequent to the combining of the complex up-converted digital signals (IUP—1, QUP—1through IUP—M, QUP—M). In this example, the combined up-converter32is subsequent to the digital quadrature modulator34. However, the combined up-converter32may alternatively be prior to the digital quadrature modulator34and subsequent to the complex digital combiner36. Note, however, that the combined up-converter32is “real” if after digital quadrature modulation but “complex” if before digital quadrature modulation.

The following acronyms are used throughout this disclosure.3GPP 3rdGeneration Partnership ProjectASIC Application Specific Integrated CircuitCDMA Code Division Multiple AccessDAC Digital-to-Analog ConverterFPGA Field Programmable Gate ArrayGHz GigahertzMHz MegahertzRF Radio Frequency