Digital transmitter, digital transmission device, and method for providing and transmitting high-frequency analog signal

Abstract

The invention relates to a digital transmitter (10) for providing a high-frequency analog signal, the transmitter comprising: conversion means (3) for receiving a digitally modulated baseband signal (12) and providing a discrete spectrum of the digitally modulated baseband signal (12) in polar coordinates or in oblique coordinates; and a synthesis means (90) for generating the high-frequency analog signal on the basis of the discrete spectrum provided in polar coordinates or in oblique coordinates, where the synthesis means (90) is a means for performing a continuous inverse Fourier transform. The invention also relates to a method for providing a high-frequency analog signal, comprising: receiving a digitally modulated baseband signal; and providing a discrete spectrum of the digitally modulated baseband signal in polar coordinates or in oblique coordinates; and generating the high-frequency analog signal based on the discrete spectrum provided in polar coordinates or in oblique coordinates by performing a continuous inverse Fourier transform.

Description

Technical Field

[0001] This invention relates to a digital transmitter for providing high-frequency analog signals. It also relates to a digital transmission device including such a transmitter. Furthermore, this invention relates to a method for providing high-frequency analog signals and a method for transmitting high-frequency analog single-carrier signals. Background Technology

[0002] Digital transmitters can be deployed in wireless digital communication systems, such as cellular networks, wireless local area networks (WLANs), or satellite communication systems. Compared to analog transmitters, digital transmitters do not require a baseband digital-to-analog converter, which leads to increased efficiency, reduced component count, improved linearity, increased bandwidth, easier calibration and compensation, and lower power consumption.

[0003] Typically, digital transmitter topologies can be distinguished by the type of coordinate system they use to represent and generate the output signal. Cartesian digital transmitters use Cartesian (orthogonal) coordinates, such as in-phase (I) and quadrature (Q) information, and generate the output signal based on them. Polar digital transmitters operate using signals represented in polar coordinates (e.g., phase and amplitude information). These topologies are illustrated in “A Wideband Energy-Efficient Multi-Mode CMOS Digital Transmitter,” M. Beikmirza et al.; IEEE Solid State Circuits Journal, Vol. 58, No. 3, March 2023, pp. 677-690.

[0004] US 11,483,186B1 discloses an exemplary digital transmitter architecture including RF circuitry that may include an IQ / polarity converter. This digital transmitter architecture uses the inverse fast Fourier transform (IFFT), an algorithm for calculating the inverse discrete Fourier transform of a carrier used for modulation of an orthogonal frequency division multiplexing (OFDM) carrier.

[0005] While digital polarity transmitters offer several advantages, they do face certain challenges, especially when wide modulation bandwidths are involved. Some of these limitations include: 1. Bandwidth Limitation: The bandwidth of the power supply modulation used to modulate the signal amplitude is typically limited. This is because the power supply and power amplifier themselves usually have limited bandwidth. As a result, the achievable modulation bandwidth of the entire system may be limited.

[0006] 2. Envelope Tracking Limitations: Envelope tracking is a common technique used in power supply modulation, where the power amplifier's supply voltage follows the envelope of the RF signal. However, envelope tracking becomes difficult after rapid changes in signal amplitude, which can degrade signal quality.

[0007] 3. Phase Modulation Challenges: In broadband applications, the phase modulator must maintain a linear and consistent group delay across the entire bandwidth, which can be difficult to achieve in practice. This becomes a bottleneck for broadband implementation of this architecture.

[0008] 4. Predistortion Limitations: Digital predistortion techniques used to compensate for nonlinearity in power amplifiers become less effective as modulation bandwidth increases. Accurately modeling and correcting nonlinear behavior over a wide bandwidth is a challenging task.

[0009] 5. Circuit complexity: Implementing power modulation and envelope tracking for broadband signals typically requires complex and power-intensive circuitry, which may negate some of the efficiency benefits of digital polarity transmitters.

[0010] 6. Non-constant envelope signals: For non-constant envelope signals (those with significantly varying amplitudes), the distortion introduced by the nonlinear PA and the limited bandwidth of the power supply modulation can become more problematic, potentially leading to a significant degrade in signal quality.

[0011] WO 2017 / 134249A1 discloses another transmitter topology that uses a Fourier domain digital-to-analog converter (DAC) to provide the transmitted signal, which is represented by and generated based on a discrete spectrum provided in Cartesian coordinates. Before transmission via the antenna, the transmitted signal is fed to and amplified by an analog power amplifier.

[0012] In light of this background, the problem to be solved is to provide a digital transmitter that exhibits less noticeable limitations with respect to modulation bandwidth and provides enhanced power efficiency. Summary of the Invention

[0013] To address this problem, the present invention proposes a digital transmitter for providing high-frequency analog signals, the transmitter comprising: A conversion device for receiving a digitally modulated baseband signal and providing the discrete spectrum of the digitally modulated baseband signal in polar or oblique coordinates, and A synthesizer is used to generate a high-frequency analog signal based on a discrete spectrum provided in polar or oblique coordinates, wherein the synthesizer is a device for performing a continuous inverse Fourier transform.

[0014] Another aspect of the invention relates to a transmission device comprising a digital transmitter for providing a high-frequency analog signal as described above and an antenna for transmitting the high-frequency analog signal, wherein the antenna is connected to the digital transmitter.

[0015] According to the present invention, the discrete spectrum of the baseband signal is provided to the synthesizer. In this respect, a representation of the digitally modulated baseband signal exists in the frequency domain. This representation can be provided to the synthesizer in polar coordinates by a conversion device, for example, phase and amplitude information for each frequency of the spectrum. Alternatively, a representation of the digitally modulated baseband signal in the frequency domain can be provided in oblique coordinates, for example, including two coordinates along non-orthogonal basis vectors. Using the discrete spectrum provided in polar or oblique coordinates, a high-frequency analog signal is synthesized in the time domain by the synthesizer.

[0016] The discrete spectrum preferably comprises multiple Fourier coefficients, which are complex coefficients, meaning they have real and imaginary components, and are provided either in polar or oblique coordinates. The Fourier coefficients are assigned to baseband frequencies, specifically where, in each case, the two baseband frequencies have a defined frequency interval (Δf). As an example, the spectrum can have N Fourier coefficients. These N Fourier coefficients can be interpreted as a measure of the spectral power of the DC component of the digital baseband signal and the spectral power of the N-1 baseband frequencies of the digital baseband signal. Each of the N-1 baseband frequencies can have an interval of Δf = BW' / N, where BW' indicates the bandwidth of the digital baseband signal.

[0017] The polar coordinate representation of the spectral components preferably includes angular and radial coordinates. Therefore, instead of representing the spectral components in two-dimensional Cartesian coordinates, such as the well-known in-phase (I) and quadrature (Q) components (I / Q), polar coordinates can be used.

[0018] The oblique coordinate representation preferably includes two coordinates along two non-orthogonal basis vectors or axes. More preferably, the oblique coordinate representation also includes a sector indicator (sector coordinates). The sector indicator can specify a sector defined by two specific non-orthogonal basis vectors from a plurality of more than two non-orthogonal basis vectors. The plurality of non-orthogonal basis vectors can, for example, include six, eight, ten, twelve, or even more non-orthogonal basis vectors. Therefore, instead of representing the components of the spectrum in two-dimensional Cartesian coordinates, such as the well-known in-phase (I) and quadrature (Q) components (I / Q), the two-dimensional I / Q space can be further divided into n sectors, each sector being defined by two basis vectors from n non-orthogonal basis vectors. The sector is indicated by the sector indicator according to which sector a specific frequency component of the spectrum is located in, and provides two coordinates along two non-orthogonal axes or basis vectors of the specified sector.

[0019] According to the present invention, the synthesis apparatus is a device for performing continuous inverse Fourier transform, thereby enabling the direct generation of analog signals, especially continuous signals, based on discrete spectra. Therefore, conventional, separate circuitry for digital-to-analog conversion, such as a digital-to-analog converter, can be omitted. Instead, the synthesis apparatus provides a means by which the transmission of a digital baseband signal present in the frequency domain to a transmission frequency range and the digital-to-analog conversion can be performed. Thus, the synthesis apparatus achieves a dual function.

[0020] Using polar or slanted coordinates allows for improved power efficiency in digital transmitters, particularly the power efficiency of synthesizers. Polar digital transmitters exhibit phase-independent efficiency for a given amplitude. Conversely, Cartesian digital transmitters exhibit phase-dependent power efficiency. When using slanted coordinates, this phase-dependent behavior is reduced because the phase difference of the basis vectors is smaller compared to the Cartesian basis vectors, which have a 90-degree phase difference.

[0021] The transmitter architecture of this invention also effectively eliminates all the aforementioned limitations regarding modulation bandwidth.

[0022] For example, a digitally modulated baseband signal can be obtained by modulating, in particular, a digital payload data stream. Modulation allows the payload data stream to be formatted suitable for a wireless transmission channel. For example, the baseband signal can be modulated using one of the following digital modulation methods: Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), Differential Phase Shift Keying (DPSK), Frequency Shift Keying (FSK), and Quadrature Amplitude Modulation (QAM). The digitally modulated baseband signal is preferably a complex-valued baseband signal, that is, it has a real part, commonly referred to as the I component or in-phase component, and an imaginary part, commonly referred to as the Q component or quadrature component.

[0023] Preferably, the high-frequency analog signal is a single-carrier signal. A high-frequency analog single-carrier signal is understood as a signal having exactly one carrier frequency, on which the information to be transmitted is modulated. In this respect, the high-frequency analog single-carrier transmission signal does not have any subcarriers. By using the transmitter according to the invention, single-carrier data transmission via a transmission channel having exactly one carrier frequency can be achieved.

[0024] Alternatively, the high-frequency analog signal is a multi-carrier signal. A high-frequency analog multi-carrier signal is understood as a signal with multiple carrier frequencies, on which the information to be transmitted is modulated. An example of multi-carrier transmission technology is orthogonal frequency division multiplexing (OFDM). Therefore, a high-frequency analog multi-carrier transmission signal has multiple subcarriers. Using the transmitter according to the invention, multi-carrier data transmission through a transmission channel having more than one carrier frequency can be achieved.

[0025] According to a preferred embodiment of the invention, the synthesizing device includes a component signal generating device for generating a plurality of phase-modulated periodic signals at component frequencies, wherein the component frequencies have a predetermined frequency interval. The predetermined frequency interval may be Δf = BW' / N, where BW' is the bandwidth of the digital baseband signal and N is the number of Fourier coefficients. Preferably, the component signal generating device is configured to generate N phase-modulated periodic signals. The phase-modulated periodic signals are periodic signals, wherein the phase of the periodic signals is changed according to a control signal provided to the component signal generating device. If the conversion device provides a spectrum in polar coordinates, the control signal is preferably a control signal representing the phase information of the Fourier coefficients. If the conversion device provides a spectrum in oblique coordinates, the control signal is preferably a control signal representing the phase information of one of the two non-orthogonal basis vectors / axes of the oblique coordinate system.

[0026] According to a preferred embodiment of the invention, the component signal generating device includes multiple digital phase-locked loops (DPLLs or ADPLLs), each configured to generate one of multiple phase-modulated periodic signals. In other words, the component signal generating device preferably has N digital phase-locked loops operating in parallel to generate N phase-modulated periodic signals (N being the number of Fourier coefficients provided to the component signal generating device). The digital phase-locked loops can be configured, for example, as described in “All-Digital PLL with Ultra Fast Settling,” RBStaszewski et al., IEEE Transactions on Circuits and Systems – II: Bulletin, Vol. 54, No. 2, February 2007, pp. 181–185.

[0027] According to a preferred embodiment of the invention, the component signal generating device is configured to receive a phase information codeword and generate a plurality of phase modulation periodic signals based on the received phase information codeword. If the conversion device provides a spectrum in polar coordinates, the phase information codeword may include phase information of the spectrum, and thus phase information of the Fourier coefficients. If the conversion device provides a spectrum in oblique coordinates, the phase information codeword may include phase information of two non-orthogonal basis vectors / axes of the oblique coordinate system.

[0028] According to a preferred embodiment of the invention, the synthesizing device includes a component signal amplitude modulation device configured to modulate the amplitudes of a plurality of phase modulation periodic signals. The component signal amplitude modulation device is preferably connected to a component signal generating device to receive the plurality of phase modulation periodic signals. The component signal amplitude modulation device can be used to individually change the amplitudes of the plurality of phase modulation periodic signals according to a control signal provided to the component signal amplitude modulation device. If the conversion device provides a spectrum in polar coordinates, the control signal is preferably a control signal representing amplitude information of the Fourier coefficients. If the conversion device provides a spectrum in oblique coordinates, the control signal is preferably a control signal representing coordinate information along two non-orthogonal basis vectors / axes of the oblique coordinate system.

[0029] According to a preferred embodiment of the invention, the component signal amplitude modulation device includes a plurality of digital power amplifiers (DPAs), each configured to modulate the amplitude of one of a plurality of phase modulation periodic signals. Preferably, the component signal amplitude modulation device includes N digital power amplifiers (where N is the number of Fourier coefficients if the spectrum is provided in polar coordinates) or 2N digital power amplifiers (where the spectrum is provided in oblique coordinates).

[0030] According to a preferred embodiment of the invention, the digital power amplifier (DPA) is a switched-capacitor power amplifier (SCPA). The digital power amplifier can be configured, for example, as described in "A Class-G Switched-Capacitor RF Power Amplifier," S.-M. Yoo et al., IEEE Solid State Circuits Journal, Vol. 48, No. 5, May 2013, pp. 1212–1224.

[0031] According to a preferred embodiment of the invention, the component signal amplitude modulation device is configured to receive an amplitude information codeword and modulate the amplitudes of a plurality of phase modulation periodic signals based on the received amplitude information codeword. If the conversion device provides a spectrum in polar coordinates, the amplitude information codeword may include amplitude information of the spectrum, thereby including amplitude information of the Fourier coefficients. If the conversion device provides a spectrum in oblique coordinates, the amplitude information codeword may include coordinate information along two non-orthogonal basis vectors / axes of the oblique coordinate system.

[0032] According to a preferred embodiment of the invention, the conversion device includes a coordinate rotating digital computer (CORDIC) or a lookup table. The conversion device preferably includes means for performing a discrete Fourier transform of the digitally modulated baseband signal, and particularly preferably includes means for performing a fast Fourier transform (FFT). The coordinate rotating digital computer (CORDIC) or lookup table can convert the result of the discrete Fourier transform (e.g., the fast Fourier transform) into a polar coordinate representation. Alternatively, the conversion device can be configured to directly determine the discrete spectrum of the digitally modulated baseband signal in polar coordinates.

[0033] To achieve the aforementioned objective, a method for providing high-frequency analog signals is also proposed, comprising: Receive digitally modulated baseband signals; and Provides the discrete spectrum of the digitally modulated baseband signal in polar or oblique coordinates; and The high-frequency analog signal is generated by performing a continuous inverse Fourier transform based on a discrete spectrum provided in polar or oblique coordinates.

[0034] According to another aspect of the present invention, a method for transmitting high-frequency analog signals is provided, comprising: The aforementioned method provides a high-frequency analog single-carrier signal, which is then transmitted via an antenna.

[0035] The method of the present invention provides the same technical effects and benefits as those discussed in conjunction with the digital transmitter and transmission device according to the present invention.

[0036] As an alternative or supplement, the advantageous configuration described in combination with the transmission equipment and / or circuitry can also be applied in this method.

[0037] Specifically, multiple phase-modulated periodic signals are generated at component frequencies, wherein the component frequencies have a predetermined frequency interval. These multiple phase-modulated periodic signals are preferably generated by a digital phase-locked loop (DPLL or ADPLL). Therefore, phase information codewords can be received, and multiple phase-modulated periodic signals can be generated based on the received phase information codewords.

[0038] Furthermore, the amplitudes of multiple phase modulation period signals can be modulated. To modulate the amplitude, multiple digital power amplifiers (DPAs) can be deployed. These DPAs can be switched-capacitor power amplifiers (SCPAs). Preferably, amplitude information codewords can be received, and the amplitudes of the multiple phase modulation period signals can be modulated based on the received amplitude information codewords.

[0039] To provide a discrete spectrum in polar coordinates, a coordinate-rotating digital computer (CORDIC) or lookup table can be deployed. A CORDIC or lookup table can convert the result of a discrete Fourier transform (e.g., a fast Fourier transform) into a polar coordinate representation. Alternatively, the discrete spectrum of a digitally modulated baseband signal can be determined directly in polar coordinates. Attached Figure Description

[0040] These and other features, characteristics, and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrate the principles of the invention by way of example. This description is given by way of example only and is not intended to limit the scope of the invention. The references to the drawings cited below refer to the accompanying drawings.

[0041] Figure 1 A digital transmitter according to a first exemplary embodiment of the present invention is shown; Figure 2 A digital transmitter according to a second exemplary embodiment of the present invention is shown; Figure 3 A digital transmitter according to a third exemplary embodiment of the present invention is shown; and Figure 4 A spectrum diagram illustrating frequency shifts across a frequency range is shown. Detailed Implementation

[0042] Figure 1 A transmission device 100 according to a first embodiment of the present invention is shown. The transmission device 100 includes a digital transmitter 10 and an antenna 20, configured to transmit high-frequency analog signals, particularly high-frequency analog single-carrier signals, provided by the transmitter 10. The transmitted signal may be a signal according to the standard IEEE 802.11 ad (wireless gigabit), with a transmission frequency band above 57 GHz, preferably in the range from 57 GHz to 66 GHz.

[0043] Digital processing device 1 provides digital baseband signal 11 to transmitter 10. According to a first embodiment, modulator 2 of transmitter 10 modulates digital baseband signal 11 to obtain digital modulated baseband signal 12. Modulator 2 may, for example, apply quadrature amplitude modulation (QAM) to digital baseband signal 11.

[0044] Transmitter 10 also includes a converter 3 for receiving the digitally modulated baseband signal 12 and providing its discrete spectrum in polar coordinates A(i), F(i). The converter 3 includes means for performing a discrete Fourier transform of the digitally modulated baseband signal 12, preferably including means for performing a Fast Fourier Transform (FFT). The converter 3 samples N symbols of the digitally modulated baseband signal 12 in the time domain and calculates the discrete spectrum of these N symbols, which has N Fourier coefficients (N-point FFT). The Fourier coefficients constitute the representation of the digitally modulated baseband signal 12 in the frequency domain. The spectrum includes complex Fourier coefficients, which are either directly determined in polar coordinates or determined in Cartesian coordinates and then converted to polar coordinates. This conversion from Cartesian polar coordinates can be accomplished using a coordinate rotation digital computer (CORDIC) or a lookup table.

[0045] The discrete spectrum available in polar coordinates A(i), F(i) is then provided to the synthesizer 90, which generates a high-frequency analog signal based on the discrete spectrum provided in polar coordinates. The synthesizer 90 is a device that performs a continuous inverse Fourier transform. It includes a component signal generation device 40 for generating N phase-modulated periodic signals 13 at component frequencies, where the component frequencies have a defined frequency interval Δf = BW' / N, where BW' is the bandwidth of the digital modulation baseband signal 12. The synthesizer 90 also includes a component signal amplitude modulation device 50, which receives the N phase-modulated periodic signals 13 and is configured to modulate the amplitude of those phase-modulated periodic signals 13.

[0046] Both the component signal generator 40 and the component signal amplitude modulator 50 receive portions of the discrete Fourier spectrum A(i) and F(i). The phase information F(i) of the discrete Fourier spectrum is fed as a codeword to the component signal generator 40, which is configured to generate multiple phase modulation periodic signals based on the received phase information codeword F(i). The amplitude information A(i) of the discrete Fourier spectrum is fed as a codeword to the component signal amplitude modulator 50, which is configured to modulate the amplitudes of the multiple phase modulation periodic signals based on the received amplitude information codeword A(i).

[0047] The component signal generation device 40 includes N digital phase-locked loops 4 (DPLL or ADPLL), each configured to generate one of a plurality of phase modulation periodic signals 13. Each digital phase-locked loop 4 is controlled by a Fourier coefficient, specifically by the phase information F(i) of a Fourier coefficient.

[0048] The component signal amplitude modulation device 50 includes N digital power amplifiers 5 (DPAs), each configured to modulate the amplitude of one of a plurality of phase modulation period signals 13. Each digital power amplifier 5 is controlled by a Fourier coefficient, specifically by amplitude information A(i) of a Fourier coefficient.

[0049] Figure 2 A second embodiment of the transmission device 100 according to the present invention is shown. The transmission device 100 largely corresponds to the transmission device of the first exemplary embodiment. Unlike the first embodiment, this transmission device 100 has a transmitter 10, to which a digital processing device provides a digitally modulated baseband signal 13. Therefore, the modulation of the digital baseband signal is performed outside the transmitter 10.

[0050] Figure 3 A third embodiment of the transmission device 100 according to the present invention is shown. Unlike the first and second embodiments, this transmission device 100 has a transmitter 10 that uses slanted coordinates to represent the component frequencies of the spectrum. Therefore, the conversion device 3 is configured to receive the digital modulation baseband signal 12 and provide the discrete spectrum A(i), F(i), A'(i), F'(i) of the digital modulation baseband signal 12 in slanted coordinates.

[0051] The synthesizer 90 includes a component signal generating device 40 for generating phase-modulated periodic signals 13 at component frequencies, here 2N phase-modulated periodic signals 13. The component frequencies have a defined frequency interval Δf = BW' / N, where BW' is the bandwidth of the digital modulation baseband signal 12. The synthesizer 90 also includes a component signal amplitude modulator 50, which receives the 2N phase-modulated periodic signals 13 and is configured to modulate the amplitude of those phase-modulated periodic signals 13.

[0052] Both the component signal generating device 40 and the component signal amplitude modulation device 50 receive portions of the discrete Fourier spectrum A(i), F(i), A'(i), and F'(i).

[0053] For each component frequency, the component signal generation device 40 generates two non-orthogonal signals corresponding to the basis vectors / axes of the slant coordinate. The conversion device provides the phase information F(i), F'(i) of those non-orthogonal signals to the component signal generation device 40, specifically the two digital phase-locked loops 4 of the component signal generation device 40. The generated component signals 13, 13' are provided by the component signal generation device 40 to the component signal amplitude modulation device 50.

[0054] The component signal amplitude modulator 50 also receives coordinate information A(i) and A'(i) along two non-orthogonal axes from the converter 3. The component signal amplitude modulator 50 is configured to modulate the amplitudes of multiple phase modulation periodic signals (two signals for each component of the spectrum) according to the received amplitude information codewords A(i) and A'(i).

[0055] The component signal amplitude modulator 50 transmits two phase modulation signals and an amplitude modulation signal for each component signal of the spectrum. These signals are summed to obtain an analog high-frequency signal 14, which is provided to the antenna 20.

[0056] The synthesizer 90 of the transmitter 10 according to the exemplary embodiment described above is designed as a means for performing a continuous inverse Fourier transform. The synthesizer 90 converts the discrete spectrum of the digital baseband signal 12 into a continuous analog transmission signal, particularly a single-carrier transmission signal, and shifts the frequency to a predetermined frequency constant f from the baseband. c The transmission frequency band. Frequencies within the transmission frequency band are assigned to the Fourier coefficients, these frequencies being spaced apart by Δf and offset from the baseband range by a specified frequency constant f relative to their corresponding frequencies. c For clarity Figure 4 As shown in the diagram. In this respect, the synthesizer 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 simultaneously performs a frequency conversion to the transmission band.

[0057] In the aforementioned transmission device 100, the digital transmitters 10 are preferably configured as integrated circuits. Each digital transmitter 10 is configured to provide a high-frequency analog signal 14, and each transmitter 10 includes: a conversion device 3 for receiving a digitally modulated baseband signal 12 and providing a discrete spectrum of the digitally modulated baseband signal 12 in polar coordinates; and a synthesis device 90 for generating a high-frequency analog signal based on the discrete spectrum provided in polar coordinates, wherein the synthesis device 90 is a device for performing a continuous inverse Fourier transform. These digital transmitters 10 exhibit relatively minor limitations in terms of modulation bandwidth.

Claims

1. A digital transmitter (10) for providing a high-frequency analog signal (14), the transmitter comprising: a conversion device (3) for receiving a digitally modulated baseband signal (12) and providing a discrete frequency spectrum (A(i), F(i)) of the digitally modulated baseband signal (12) in polar coordinates or in slant 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 slant coordinates, wherein the synthesis device (90) is a device for performing a continuous inverse Fourier transform.

2. The digital transmitter (10) of claim 1, wherein the synthesis device (90) comprises a component signal generation device (40) for generating a plurality of phase-modulated periodic signals on component frequencies, wherein the component frequencies have a prescribed frequency spacing.

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

4. The digital transmitter (10) of any one of claims 2 or 3, wherein the component signal generation device (40) is configured to receive a phase information codeword (F(i)) and to generate the plurality of phase-modulated periodic signals in accordance with the received phase information codeword (F(i)).

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

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

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

8. The digital transmitter (10) of any one of claims 5 to 7, wherein the component signal amplitude modulation device (50) is configured to receive an amplitude information codeword (A(i)) and to modulate the amplitudes of the plurality of phase-modulated periodic signals (13) in accordance with the received amplitude information codeword (A(i)).

9. The digital transmitter (10) of any one of the preceding claims, wherein the conversion device (3) comprises a coordinate rotation digital computer, CORDIC, or a lookup table.

10. The digital transmitter (10) according to any one of the preceding claims, wherein the conversion device (3) comprises means for performing a discrete Fourier transform of the digitally modulated baseband signal (12), particularly preferably means for performing a fast Fourier transform, FFT.

11. The digital transmitter according to any one 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 one 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. A method for providing a high-frequency analog signal (14), comprising: receiving a digitally modulated baseband signal (12); and providing a discrete spectrum (A(i), F(i)) of the digitally modulated baseband signal (12) in polar coordinates or in slant coordinates; and generating the high-frequency analog signal (14) by performing a continuous inverse Fourier transform based on the provided discrete spectrum (A(i), F(i)) in polar coordinates or in slant coordinates.

14. A method for transmitting a high-frequency analog single-carrier signal (14), comprising providing a high-frequency analog signal (14) according to the method of claim 13 and transmitting the high-frequency analog single-carrier signal (14) via an antenna (20).

15. The method of any one of claims 13 or 14, wherein, The high-frequency analog signal (14) is a single-carrier signal.

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