A digital transmitter, a digital transmission device, and methods for providing and transmitting a high-frequency, analog signal

Abstract

The invention concerns a digital transmitter (10) for providing a high-frequency, analog signal, the transmitter comprising: a conversion device (3) for receiving a digital, modulated baseband signal (12) and providing a discrete frequency spectrum of the digital, modulated baseband signal (12) in polar coordinates or in skew coordinates, and a synthesis device (90) for generating the high-frequency analog signal based on the discrete frequency spectrum provided in polar coordinates or in skew coordinates, wherein the synthesis device (90) is a device for carrying out a continuous, inverse Fourier transformation. The invention further concerns a method for providing a high-frequency, analog signal, comprising: receiving a digital, modulated baseband signal; and providing a discrete frequency spectrum of the digital, modulated baseband signal in polar coordinates or in skew coordinates; and generating the high-frequency analog signal based on the discrete frequency spectrum provided in polar coordinates or in skew coordinates by carrying out a continuous, inverse Fourier transformation.

Description

[0001] A digital transmitter, a digital transmission device, and methods for providing and transmitting a high-frequency, analog signal

[0002] The invention concerns a digital transmitter for providing a high-frequency, analog signal. The invention further concerns a digital transmission device comprising such transmitter. Additionally, the invention concerns a method for providing a high-frequency, analog signal and a method for transmitting a high-frequency, analog single carrier signal.

[0003] Digital transmitters can be deployed in wireless, digital communication systems as for example cellular networks, wireless local area networks (WLAN) or satellite communication systems. As compared to analog transmitters, digital transmitters do not require baseband digital-to- analog converters which results in increased efficiency, reduced component count, improved linearity, enhanced bandwidth, easier calibration and compensation and reduced power consumption.

[0004] Generally, digital transmitter topologies may be distinguished by the type of coordinate system they use for representing and generating the output signal. Cartesian digital transmitters use cartesian (quadrature) coordinates, e.g., in-phase (I) and quadrature (Q) information and generate the output signal based thereon. Polar digital transmitters work with signals represented in polar coordinates, e.g., a phase and an amplitude information. Those topologies are elucidated in “A Wideband Energy-Efficient Multi-Mode CMOS Digital Transmitter”, M. Beikmirza et al.; IEEE Journal of Solid-State Circuits, Vol 58. No. 3, March 2023, pa. 677-690.

[0005] An exemplary digital transmitter architecture including RF circuitry that may include an IQ / polar converter is disclosed in US 11 ,483,186 B1. This digital transmitter architecture uses inverse fast Fourier transformation (IFFT) - an algorithm that computes the inverse discrete Fourier transform - for modulating an orthogonal frequency division multiplexing (OFDM) carrier.

[0006] While digital polar transmitters offer several advantages, they do face certain challenges, particularly when it comes to wide modulation bandwidth. Some of these limitations include:

[0007] 1. Bandwidth Limitation: The bandwidth of supply modulation, which is used to modulate the amplitude of the signal, is typically limited. This is because the power supply and the power amplifier itself often have limited bandwidths. As a result, the achievable modulation bandwidth of the whole system can be constrained.

[0008] 2. Envelope Tracking Limitations: Envelope tracking is one of the common techniques used for supply modulation, where the supply voltage of the power amplifier follows the envelope of the RF signal. However, envelope tracking has difficulties following rapid changes in signal amplitude, which can degrade signal quality.

[0009] 3. Phase Modulation Challenges: In wideband applications, the phase modulator has to maintain linearity and consistent group delay across the full bandwidth, which can be difficult to achieve in practice. This presents a bottleneck for the wideband implementation of this architecture.

[0010] 4. Predistortion Limitations: Digital predistortion techniques, which are used to compensate for the nonlinearity of power amplifiers, can become less effective as the modulation bandwidth increases. Accurately modeling and correcting the non-linear behavior over a wide bandwidth is a challenging task.

[0011] 5. Circuit Complexity: Implementing supply modulation and envelope tracking for wideband signals often requires complex and power-hungry circuits, which can negate some of the efficiency benefits of the digital polar transmitter.

[0012] 6. Non-Constant Envelope Signals: For non-constant envelope signals (those where amplitude varies significantly), the distortions introduced by the non-linear PA and the limited bandwidth of supply modulation can become more problematic, potentially leading to a significant reduction in signal quality.

[0013] In WO 2017 / 134249 A1 yet another transmitter topology is disclosed which uses a Fourier domain digital-to-analog converter that provides a transmission signal which is represented by and generated based on a discrete frequency spectrum provided in cartesian coordinates. The transmission signal is fed to and amplified by an analog power amplifier before transmission via an antenna.

[0014] Against this background the problem to be solved is to provide a digital transmitter that shows less pronounced limitations regarding modulation bandwidth and provides enhanced power efficiency.

[0015] For solving the problem, the invention proposes a digital transmitter for providing a high- frequency, analog signal, the transmitter comprising: a conversion device for receiving a digital, modulated baseband signal and providing a discrete frequency spectrum of the digital, modulated baseband signal in polar coordinates or in skew coordinates, and a synthesis device for generating the high-frequency analog signal based on the discrete frequency spectrum provided in polar coordinates or in skew coordinates, wherein the synthesis device is a device for carrying out a continuous, inverse Fourier transformation Another aspect of the invention concerns a transmission device comprising a digital transmitter for providing a high-frequency, analog signal as mentioned before and an antenna for transmitting the high-frequency, analog signal, wherein the antenna is connected to the digital transmitter.

[0016] According to the invention, a discrete frequency spectrum of a baseband signal is provided to the synthesis device. In this respect, there is a representation of the digital, modulated baseband signal in the frequency domain. This representation can be provided by the conversion device to the synthesis device in polar coordinates, e.g., a. phase and an amplitude information for each frequency of the frequency spectrum. Alternatively, the representation of the digital, modulated baseband signal in the frequency domain can be provided in skew coordinates, e.g., comprising two coordinates along non-orthogonal basis vectors. Using the discrete frequency spectrum provided in polar coordinates or skew coordinates, the high- frequency analog signal is synthesized in the time domain by means of the synthesis device.

[0017] The discrete frequency spectrum preferably comprises a plurality of Fourier coefficients, which are complex coefficients, that is to say they have a real and an imaginary component, which are either provided in polar coordinates or in skew coordinates. The Fourier coefficients are each assigned to a baseband frequency, in particular wherein in each case two baseband frequencies have a prescribed frequency spacing (Af). By way of example, the frequency spectrum can have N Fourier coefficients. The N Fourier coefficients can be construed as a measure of the spectral power of the DC component of the digital baseband signal as well as of the spectral power of N-1 baseband frequencies of the digital baseband signal. The N-1 baseband frequencies can each have a spacing of Af = BW7N, wherein BW‘ indicates the bandwidth of the digital baseband signal.

[0018] The polar coordinate representation of the components of the frequency spectrum preferably comprises an angular and a radial coordinate. Thus, instead of representing the components of the frequency spectrum in two-dimensional cartesian coordinates, e.g. the well-known in- phase (I) and quadrature (Q) components (l / Q), polar coordinates may be used.

[0019] The skew coordinate representation preferably comprises two coordinates along two non- orthogonal basis vectors or axes. More preferably, the skew coordinate representation additionally comprises a sector indication (sector coordinate). The sector indication may specify a sector defined by two specific non-orthogonal basis vectors out of a plurality of more than two non-orthogonal basis vectors. The plurality of non-orthogonal basis vectors may, e.g. comprise six or eight or ten or twelve or even more non-orthogonal basis vectors. Thus, instead of representing the components of the frequency spectrum in two-dimensional cartesian coordinates, e.g. the well-known in-phase (I) and quadrature (Q) components (l / Q), the two- dimensional l / Q-space may be subdivided into n sectors each limited by two of n non- orthogonal basis vectors. Dependend on in which sector a specific frequency component of the frequency spectrum is located at, the sector is indicated by the sector indication and two coordinates are provided along the two non-orthogonal axes or basis vectors of the specified sector.

[0020] According to the invention, the synthesis apparatus is an apparatus for carrying out a continuous, inverse Fourier transformation so that an analog, in particular continuous, signal can be generated directly on the basis of the discrete frequency spectrum. It is therefore possible to omit a conventional, separate circuit for digital-to-analog conversion, for example a digital-to-analog converter. Instead, the synthesis apparatus provides an apparatus by means of which both transmission of the digital baseband signal present in the frequency domain to a transmission frequency range and digital-to-analog conversion can be carried out. The synthesis apparatus thus fulfills a double function.

[0021] Using either the polar coordinate representation or the skew coordinate representation allows to enhance the power efficiency of the digital transmitter, in particular of the synthesis apparatus of the digital transmitter. Polar digital transmitters exhibit phase-independent efficiency for a given amplitude. In contrast, cartesian digital transmitters suffer from a phasedependent power efficiency. This phase-dependent behavior is reduced when using skew coordinates due to the smaller phase difference of the basis vectors as compared to cartesian basis vectors with 90 degree phase difference.

[0022] The inventive transmitter architecture also effectively eliminates all previously mentioned limitations regarding modulation bandwidth.

[0023] The digital, modulated baseband signal can be obtained, for example, through modulation of an, in particular digital, payload data stream. The payload data stream can be brought to a format adapted to the wireless transmission channel through the modulation. The modulated baseband signal can be modulated, for example, by means of one of the digital modulation methods mentioned below: Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), Differential Phase Shift Keying (DPSK), Frequency Shift Keying (FSK), Quadrature Amplitude Modulation (QAM). The digital, modulated baseband signal is preferably a complex-valued baseband signal, that is to say it has a real component, which is usually referred to as I component or in-phase component, and an imaginary component, which is usually referred to as Q component or quadrature component.

[0024] Preferably, the high-frequency, analog signal is a single-carrier signal. A high-frequency, analog single-carrier signal is understood to be a signal that has precisely one carrier frequency, onto which the information to be transferred is modulated. In this respect, the high- frequency, analog single-carrier transmission signal does not have any subcarriers. Singlecarrier data transmission by means of a transmission channel can be made possible using the transmitter according to the invention, wherein the transmission channel has precisely one carrier frequency.

[0025] Alternatively, the high-frequency, analog signal is a multi-carrier signal. A high-frequency, analog multi-carrier signal is understood to be a signal that has multiple carrier frequencies, onto which the information to be transferred is modulated. One example of a multi-carrier transmission technique is orthogonal frequency-division multiplexing (OFDM). Thus, the high- frequency, analog multi-carrier transmission signal has multiple subcarriers. Multiple-carrier data transmission by means of a transmission channel can be made possible using the transmitter according to the invention, wherein the transmission channel has more than one carrier frequency.

[0026] According to a preferred embodiment of the invention, the synthesis device comprises a component signals generation device for generating multiple phase-modulated periodic signals at component frequencies, wherein the component frequencies have a prescribed frequency spacing. The prescribed frequency spacing can be Af = BW7N, wherein BW‘ is the bandwidth of the digital baseband signal and N is the number of Fourier coefficients. Preferably, the component signals generations device is configured for generating N phase-modulated periodic signals. Phase modulated periodic signals are periodic signals wherein the phase of the periodic signal is changed according to a control signal provided to the component signals generation device. If the conversion device provides the frequency spectrum in polar coordinates, the control signal is preferably a control signal representing phase information of a Fourier coefficient. If the conversion device provides the frequency spectrum in skew coordinates, the control signal is preferably a control signal representing phase information of one of the two non-orthogonal base vectors / axes of the skew coordinate system.

[0027] According to a preferred embodiment of the invention, the component signals generation device comprises multiple digital phase-locked loops, DPLLs or ADPLLs, each configured to generate one of the multiple phase-modulated periodic signals. In other words, the component signals generation device preferably has N digital phase-locked loops working in parallel in order to generate N phase-modulated periodic signals (N being the number of Fourier coefficients provided to the component signals generation device). The digital phase-locked loops may, e.g., be configured as described in “All-Digital PLL with Ultra Fast Settling”, R. B. Staszewski et al.; IEEE Transactions on Circuits and Systems - II: Express Briefs, Vol. 54, No. 2, February 2007, p. 181-185.

[0028] According to a preferred embodiment of the invention, the component signals generation device is configured to receive a phase information code word and generate the multiple phase-modulated periodic signals depending on the received phase information code word. If the conversion device provides the frequency spectrum in polar coordinates, the phase information code word may comprise the phase information of the frequency spectrum, thus, the phase information of the Fourier coefficients. If the conversion device provides the frequency spectrum in skew coordinates, the phase information code word may comprise the phase information of the two non-orthogonal base vectors / axes of the skew coordinate system.

[0029] According to a preferred embodiment of the invention, the synthesis device comprises a component signals amplitude modulation device configured to modulate the amplitudes of the multiple phase-modulated periodic signals. The component signals amplitude modulation device is preferably connected to the component signals generation device so as to receive the multiple phase-modulated periodic signals. The component signals amplitude modulation device may be employed to individually change the amplitudes of the multiple phase- modulated periodic signals according to control signals provided to the component signals amplitude modulation device. If the conversion device provides the frequency spectrum in polar coordinates, the control signals are preferably control signals representing amplitude information of the Fourier coefficients. If the conversion device provides the frequency spectrum in skew coordinates, the control signals are preferably control signals representing the coordinate information along the two non-orthogonal base vectors / axes of the skew coordinate system.

[0030] According to a preferred embodiment of the invention, the component signals amplitude modulation device comprises multiple digital power amplifiers, DPAs, each configured to modulate the amplitude of one of the multiple phase-modulated periodic signals. Preferably the component signals amplitude modulation device comprises N digital power amplifiers (N being the number of Fourier coefficients - if the frequency spectrum is provided in polar coordinates) or 2N digital powered amplifiers (if the frequency spectrum is provided in skew coordinates). According to a preferred embodiment of the invention, the digital power amplifiers, DPAs, are switched-capacitor power amplifiers, SCPAs. The digital power amplifiers may, e.g., be configured as described in “A Class-G Switched-Capacitor RF Power Amplifier”, S.-M. Yoo et al., IEEE Journal of Solid-State Circuits, Vol 48, No. 5, May 2013, Page 1212-1224.

[0031] According to a preferred embodiment of the invention, the component signals amplitude modulation device is configured to receive an amplitude information code word and modulate the amplitude of the multiple phase-modulated periodic signals depending on the received amplitude information code word. If the conversion device provides the frequency spectrum in polar coordinates, the amplitude information code may comprise the amplitude information of the frequency spectrum, thus, the amplitude information of the Fourier coefficients. If the conversion device provides the frequency spectrum in skew coordinates, the amplitude information code word may comprise the coordinate information along both the two non- orthogonal base vectors / axes of the skew coordinate system.

[0032] According to a preferred embodiment of the invention, the conversion device comprises a Coordinate Rotation Digital Computer, CORDIC, or a lookup table. The conversion device preferably comprises an apparatus for carrying out a discrete Fourier transformation of the digital, modulated baseband signal, particularly preferably an apparatus for carrying out a fast Fourier transformation (FFT). The Coordinate Rotation Digital Computer, CORDIC, or the lookup table may convert the result of the discrete Fourier transformation, e.g., of the fast Fourier transformation, to a representation in polar coordinates. Alternatively, the conversion device may be configured to directly determine the discrete frequency spectrum of the digital, modulated baseband signal in polar coordinates.

[0033] To achieve the object mentioned at the beginning, a method for providing a high-frequency, analog signal is also proposed, comprising: receiving a digital, modulated baseband signal; and providing a discrete frequency spectrum of the digital, modulated baseband signal in polar coordinates or in skew coordinates; and generating the high-frequency analog signal based on the discrete frequency spectrum provided in polar coordinates or in skew coordinates by carrying out a continuous, inverse Fourier transformation.

[0034] According to yet another aspect of the invention, a method for transmitting a high-frequency analog signal is proposed, comprising providing the high-frequency analog single carrier signal according to the previously mentioned method and transmitting the high-frequency analog signal via an antenna.

[0035] The inventive methods provide the same technical effects and benefits as discussed in conjunction with the digital transmitter and the transmission device according to the invention.

[0036] As an alternative or in addition, in the method, the advantageous configurations described in connection with the transmission device and / or the circuit arrangement can also be applied.

[0037] In particular, multiple phase-modulated periodic signals are generated at component frequencies, wherein the component frequencies have a prescribed frequency spacing. Those multiple phase-modulated periodic signals may preferably be generated by digital phase- locked loops, DPLLs or ADPLLs. A phase information code word may therefore be received and the multiple phase-modulated periodic signals may be generated depending on the received phase information code word.

[0038] Furthermore, the amplitudes of the multiple phase-modulated periodic signals may be modulated. For modulation of the amplitudes, the multiple digital power amplifiers, DPAs, may be deployed. Those digital power amplifiers may be switched-capacitor power amplifiers, SCPAs. Preferably, an amplitude information code word may be received and the amplitude of the multiple phase-modulated periodic signals may be modulated depending on the received amplitude information code word.

[0039] For providing the discrete frequency spectrum in polar coordinates, a Coordinate Rotation Digital Computer, CORDIC, or a lookup table may be deployed. The Coordinate Rotation Digital Computer, CORDIC, or the lookup table may convert the result of a discrete Fourier transformation, e.g., of A fast Fourier transformation, to a representation in polar coordinates. Alternatively, the discrete frequency spectrum of the digital, modulated baseband signal may directly be determined in polar coordinates.

[0040] These and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0041] Fig. 1 shows a digital transmitter according to a first exemplary embodiment of the invention; Fig. 2 shows a digital transmitter according to a second exemplary embodiment of the invention;

[0042] Fig. 3 shows a digital transmitter according to a third exemplary embodiment of the invention; and

[0043] Fig. 4 shows a spectral diagram for illustrating the frequency shift in the frequency range.

[0044] Fig. 1 shows a transmission device 100 according to a first exemplary embodiment of the invention. The transmission device 100 includes a digital transmitter 10 and an antenna 20 configured for transmitting a high-frequency, analog signal provided by the transmitter 10, in particular a high-frequency, analog single-carrier signal. The transmitted signal may be a signal according to the standard IEEE 802.11 ad (Wireless Gigabit) in a transmission frequency band above 57 GHz, preferably in a range of from 57 GHz to 66 GHz.

[0045] A digital baseband signal 11 is provided to the transmitter 10 by a digital processing device 1. According to the first embodiment, a modulator 2 of the transmitter 10 modulates the digital baseband signal 11 to obtain a digital, modulated baseband signal 12. The modulator 2 may, e.g., apply Quadrature Amplitude Modulation (QAM) to the digital baseband signal 11.

[0046] The transmitter 10 further includes a conversion device 3 for receiving the digital, modulated baseband signal 12 and providing a discrete frequency spectrum of the digital, modulated baseband signal 12 in polar coordinates A(i), F(i). The conversion device 3 comprises an apparatus for carrying out a discrete Fourier transformation of the digital, modulated baseband signal 12, preferably an apparatus for carrying out a fast Fourier transformation (FFT). The conversion device 3 samples N symbols of the digital, modulated baseband signal 12 in the time domain and calculates a discrete frequency spectrum for these N symbols, which discrete frequency spectrum has N Fourier coefficients (N-point-FFT). The Fourier coefficients constitute a representation of the digital, modulated baseband signal 12 in the frequency domain. The frequency spectrum comprises complex Fourier coefficients which are either directly determined in polar coordinates or are determined in cartesian coordinates and then converted into polar coordinates. Such conversion from cartesian int polar coordinates may be accomplished by a Coordinate Rotation Digital Computer (CORDIC) or a lookup table. The discrete frequency spectrum which is available in polar coordinates A(i), F(i) is then provided to a synthesis device 90 which generates a high-frequency analog signal based on the discrete frequency spectrum provided in polar coordinates. The synthesis device 90 is a device that carries out a continuous, inverse Fourier transformation. It comprises a component signals generation device 40 for generating N phase-modulated periodic signals 13 at component frequencies, wherein the component frequencies have a prescribed frequency spacing Af = BW7N, wherein BW‘ is the bandwidth of the digital, modulated baseband signal

[0047] 12. The synthesis device 90 further comprises a component signals amplitude modulation device 50 which receives the N phase-modulated periodic signals 13 and is configured to modulate the amplitudes of those phase-modulated periodic signals 13.

[0048] Both, the component signals generation device 40 and the component signals amplitude modulation device 50 receive parts of the discrete Fourier spectrum A(i), F(i). The phase information F(i) of the discrete Fourier spectrum is fed as a code word to the component signals generation device 40 which is configured and generate the multiple phase-modulated periodic signals depending on the received phase information code word F(i). The amplitude information A(i) of the discrete Fourier spectrum is fed as a code word to the component signals amplitude modulation device 50 which is configured to modulate the amplitude of the multiple phase-modulated periodic signals depending on the received amplitude information code word A(i).

[0049] The component signals generation device 40 comprises N digital phase-locked loops 4, DPLLs or ADPLLs, each configured to generate one of the multiple phase-modulated periodic signals

[0050] 13. Each digital phase-locked loop 4 is controlled by one Fourier coefficient, in particular by the phase information F(i) of one Fourier coefficient.

[0051] The component signals amplitude modulation device 50 comprises N digital power amplifiers 5, DPAs, each configured to modulate the amplitude of one of the multiple phase-modulated periodic signals 13. Each digital power amplifier 5 is controlled by on Fourier coefficient, in particular by the amplitude information A(i) of one Fourier coefficient.

[0052] Fig. 2 shows a second exemplary embodiment of a transmission device 100 according to the invention. The transmission device 100 corresponds in large parts to the transmission de-vice of the first exemplary embodiment. In contrast to the first exemplary embodiment, this transmission device 100 has a transmitter 10 to which a digital, modulated baseband signal 13 is provided by a digital processing device. Thus, the modulation of the digital baseband signal is carried out external to the transmitter 10. Fig. 3 shows a third exemplary embodiment of a transmission device 100 according to the invention. In contrast to the first and second exemplary embodiments, this transmission device 100 has a transmitter 10 that makes use of skew coordinates to represent the component frequencies of the frequency spectrum. Thus, the conversion device 3 is configured for receiving a digital, modulated baseband signal 12 and providing a discrete frequency spectrum A(i), F(i), A’(i), F’(i) of the digital, modulated baseband signal 12 in skew coordinates.

[0053] The synthesis device 90 comprises a component signals generation device 40 for generating phase-modulated periodic signals 13 at component frequencies, here 2N phase-modulated periodic signals 13. The component frequencies have a prescribed frequency spacing Af = BW7N, wherein BW‘ is the bandwidth of the digital, modulated baseband signal 12. The synthesis device 90 further comprises a component signals amplitude modulation device 50 which receives the 2N phase-modulated periodic signals 13 and is configured to modulate the amplitudes of those phase-modulated periodic signals 13.

[0054] Both, the component signals generation device 40 and the component signals amplitude modulation device 50 receive parts of the discrete Fourier spectrum A(i), F(i), A’(i), F’(i).

[0055] For each component frequency, the component signals generation device 40 generates two non-orthogonal signals which correspond to the base vectors / axes of the skew coordinates. The conversion device provides phase information F(i), F’(i) for those non-orthogonal signals to the component signals generation device 40, in particular to two digital phase-locked loops 4 of the component signals generation device 40. The generated component signals 13, 13’ are provided by the component signals generation device 40 to the component signals amplitude modulation device 50.

[0056] The component signals amplitude modulation device 50 also receives coordinate information A(i), A’(i) along the two non-orthogonal axes from the conversion device 3. The component signals amplitude modulation device 50 is configured to modulate the amplitudes of the multiple phase-modulated periodic signals (two signals for each component signal of the frequency spectrum) depending on the received amplitude information code word A(i), A’(i).

[0057] The component signals amplitude modulation device 50 delivers two phase- and amplitude- modulated signals for each of the component signals of the frequency spectrum. Those signals are summed to obtain the analog high-frequency signal 14 which is provided to the antenna 20. The synthesis device 90 of the transmitters 10 according to the exemplary embodiments described before, is designed as an apparatus for carrying out a continuous, inverse Fourier transformation. The synthesis device 90 converts the discrete frequency spectrum of the digital baseband signal 12 to a continuous, analog transmission signal, in particular a single-carrier transmission signal, and shifts the frequency to a transmission frequency band, which is shifted from the baseband by a prescribed frequency constant fc. Frequencies in the transmission frequency band are assigned to said Fourier coefficients, which frequencies each have a spacing of f with respect to one another and are shifted with respect to the corresponding frequencies from the baseband range by the prescribed frequency constant fc, as is illustrated in Fig. 4 for clarification. In this respect, the synthesis device 90 can be referred to as a polar RF-FAC (Radio Frequency Fourier-to-Analog Converter), which transmits the baseband signal from the frequency domain (in polar coordinates) back to the time domain and at the same time carries out frequency transformation to the transmission frequency band.

[0058] In the transmission devices 100 described above, the digital transmitter 10 is preferably configured as an integrated circuit. The digital transmitters 10 are each configured for providing a high-frequency, analog signal 14. The transmitters 10 each comprise a conversion device 3 for receiving a digital, modulated baseband signal 12 and providing a discrete frequency spectrum of the digital, modulated baseband signal 12 in polar coordinates, and a synthesis device 90 for generating the high-frequency analog signal based on the discrete frequency spectrum provided in polar coordinates, wherein the synthesis device 90 is a device for carrying out a continuous, inverse Fourier transformation. Those digital transmitters 10 show less pronounced limitations regarding modulation bandwidth.

Claims

Patent Claims1. A digital transmitter (10) for providing a high-frequency, analog signal (14), the transmitter comprising: a conversion device (3) for receiving a digital, modulated baseband signal (12) and providing a discrete frequency spectrum (A(i), F(i)) of the digital, modulated baseband signal (12) in polar coordinates or in skew coordinates, and a synthesis device (90) for generating the high-frequency analog signal (14) based on the discrete frequency spectrum (A(i), F(i)) provided in polar coordinates or in / skew coordinates, wherein the synthesis device (90) is a device for carrying out a continuous, inverse Fourier transformation.

2. Digital transmitter (10) according to claim 1, wherein the synthesis device (90) comprises a component signals generation device (40) for generating multiple phase- modulated periodic signals at component frequencies, wherein the component frequencies have a prescribed frequency spacing.

3. Digital transmitter (10) according to claim 2, wherein the component signals generation device (40) comprises multiple digital phase-locked loops (4), DPLLs or ADPLLs, each configured to generate one of the multiple phase-modulated periodic signals.

4. Digital transmitter (10) according to any of claims 2 or 3, wherein the component signals generation device (40) is configured to receive a phase information code word (F(i)) and generate the multiple phase-modulated periodic signals depending on the received phase information code word (F(i)).

5. Digital transmitter (10) according to any of claims 2 to 4, wherein the synthesis device (90) comprises a component signals amplitude modulation device (50) configured to modulate the amplitudes of the multiple phase-modulated periodic signals (13).

6. Digital transmitter (10) according to claim 5, wherein the component signals amplitude modulation device (50) comprises multiple digital power amplifiers (5), DPAs, each configured to modulate the amplitude of one of the multiple phase-modulated periodic signals (13).

7. Digital transmitter (10) according to claim 6, wherein the digital power amplifiers (5), DPAs, are switched-capacitor power amplifiers, SCPAs.

8. Digital transmitter (10) according to any of claims 5 to 7, wherein the component signals amplitude modulation device (50) is configured to receive an amplitude information code word (A(i)) and modulate the amplitude of the multiple phase- modulated periodic signals (13) depending on the received amplitude information code word (A(i)).

9. Digital transmitter (10) according to any of the preceding claims, wherein the conversion device (3) comprises a Coordinate Rotation Digital Computer, CORDIC, or a lookup table.

10. Digital transmitter (10) according to any of the preceding claims, wherein the conversion device (3) comprises an apparatus for carrying out a discrete Fourier transformation of the digital, modulated baseband signal (12), particularly preferably an apparatus for carrying out a fast Fourier transformation, FFT.

11. Digital transmitter according to any of the preceding claims, wherein the high- frequency, analog signal (14) is a single-carrier signal.

12. A transmission device (100) comprising a digital transmitter (10) for providing a high- frequency, analog signal (14) according to any of the preceding claims and an antenna (20) for transmitting the high-frequency, analog signal, (14) wherein the antenna (20) is connected to the digital transmitter (10).

13. Method for providing a high-frequency, analog signal (14), comprising: receiving a digital, modulated baseband signal (12); and providing a discrete frequency spectrum (A(i), F(i)) of the digital, modulated baseband signal (12) in polar coordinates or skew coordinates; and generating the high-frequency analog signal (14) based on the discrete frequency spectrum (A(i), F(i)) provided in polar coordinates or skew coordinates by carrying out a continuous, inverse Fourier transformation.

14. Method for transmitting a high-frequency analog single-carrier signal (14) comprising providing the high-frequency analog signal (14) according a method according to claim 13 and transmitting the high-frequency analog single-carrier signal (14) via anantenna (20).

15. Method according to any of claims 13 or 14, wherein the high-frequency, analog signal (14) is a single-carrier signal.

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