WO2001008370A1

WO2001008370A1 - Modulation switch for the generation of a similtaneously phase- and amplitude modulated signal

Info

Publication number: WO2001008370A1
Application number: PCT/DE2000/001269
Authority: WO
Inventors: Ludwig Hofmann
Original assignee: Siemens Aktiengesellschaft
Priority date: 1999-07-21
Filing date: 2000-04-25
Publication date: 2001-02-01
Also published as: EP1197051A1

Abstract

This invention concerns a modulation switch (1) for the generation of a similtaneously phase- and amplitude-modulated HF-signal, in particular a QAM-HF-signal having a digital phase modulated stage (7) and final stage switched to thereto (15), which is connected via a first direct input or via a power control stage (13) to the output of the phase modulator stage, whereby one of the digital amplitude signal generation stages is separated from the phase modulator stage (5, 13) and is connected at least indirectly on the output side to a second input of the end stage or the power control step.

Description

description

MODULATION CIRCUIT TO GENERATE A PHASE AND AMPLITUDE MODULATED SIGNAL

The invention relates to a modulation circuit for generating an RF signal that is simultaneously phase and amplitude modulated according to the preamble of claim 1.

Finally, digital modulation methods are used in modern cellular mobile radio systems. These are characterized by a high bandwidth efficiency, a favorable current account, high Storfestigkeit and advantageous Implementierungseigenscnaften, especially among αen Ge ^¬ the fortscnreitenden miniaturization view points αer Mo bilfunk-Endgerate and αes high cost pressure in their implementation.

As with analog modulation methods, there are basic possibilities of amplitude or phase modulation in digital modulation methods for impressing a message signal, which has a nier digital form, onto a carrier signal, the latter concepting frequency and phase shift keying as two relatively independent variants includes.

In particular, the method of phase shift keying or PSK (phase shift keymg) modulation is used today both in digital mobile radio systems and in radio and satellite radio technology. The manipulation of frequency shift keying (FSK Frequency Shift Keymg) modulation, in which the modulation information emits a change in frequency of the carrier signal, is also detaoled. If, in the interest of high bandwidth efficiency, em is quickly used from one frequency to another switched oscillator, one obtains continuous phase changes during the transition from one symbol to another, which is why this method is called CPFSK (Contmuous Phase Frequency Shift Keymg) process is called.

The applicants have described advantageous modulation circuits for implementing digital frequency or phase modulation methods in DE-A-197 40 196 and DE-A-197 52 438.

In the context of the development of a future standard for mobile radio systems with significantly increased transmission capacity and flexibility, the method of quality amplitude modulation (QAM) is becoming increasingly important. Higher-order QAM processes in particular have advantages in terms of interference safety and reliability compared to PSK processes, but place high demands on the implementation of the transmission output stages.

As a modulator circuit for quadrature modulation methods (including the QPSK (Quadrature Phase Snift Keymg) modulation method already established in mobile radio systems), so-called Qudrature modulators are usually used, which allow the generation of frequency or phase-modulated signals with high frequency or phase accuracy , However, these modulators have a complex analog part, require the use of closely tolerated components and are only of limited suitability for a (highly) integrated design.

A large number of known modulator concepts provide for the control of a voltage-controlled oscillator (VCO) via a phase locked loop (PLL = phase locked loop) in order to generate spectrally pure signals. An output signal with a constant amplitude is amplified in an output stage, which in this case can work non-linearly and is relatively simple and can be implemented with sufficient efficiency. In this context it is also known to use a modulated signal with a non-constant amplitude thereof Envelope to be recorded separately and fed to a power control circuit separately. A similar concept, which is also known as the "envelope curve elimination and restoration method", is used to increase the efficiency of the transmitting end stage of the satellite radio technology.

The object of the invention is to provide a modulation circuit of the generic type which is improved, in particular with regard to the expenditure on discrete components and from a cost point of view.

This object is achieved by a modulation circuit with the features of claim 1.

The invention concludes the fundamental idea of assigning separate frequency, phase and amplitude and amplitude information to a stream of data words or symbols for realizing the greatest possible digital modulation processing ar> mitio and this information in a digital phase modulator stage on the one hand and a digital amplitude signal generator stage on the other hand to process separately in the reception area of the transmission stage. The major part of the technical effort for the modulation lies in the digitalization and digital processing, which, however, is known to be extremely precise and highly integrable. Components can be realized. This results in a significant reduction in the cost of discrete components and, overall, the cost.

The proposed modulation circuit can be referred to as a "polar actuator", since its operation based on the separate processing of phase and amplitude information can advantageously be described in a polar coordinate system.

On the output side of the amplitude signal generator stage, either the input of the output stage or the input of a power control stage is connected directly. In a more advantageous Embodiment is here em Dιgιtal- / analog converter zwischenge ^¬ on, the zeugerstufe the digital output of the Amplituoensignaler- to an analog input of the power amplifier or power control stage connects.

In a further preferred embodiment, this analog process is additionally connected to the output of the output stage via a power control loop.

The implementation of the data stream m the modulation information is alternatively carried out using assignment tables or by real-time calculation based on a predetermined algorithm. Correspondingly, in a first embodiment of a digital signal processor stage, an assignment memory for storing a table-like assignment rule of an input-side data bit stream m has the modulation information consisting of a sequence of phase-amplitude value pairs. In another embodiment, the signal processor stage has a calculation unit for real-time calculation of the mentioned phase-amplitude value pairs from the data bit stream on the basis of a calculation algorithm stored in an assigned program memory.

In a further preferred embodiment, the phase modulator stage has a voltage-controlled oscillator which is controlled directly or indirectly (especially via a D / A converter) by means of a digital phase modulation signal. In a further preferred embodiment, the phase modulator stage comprises a frequency synthesis circuit, which in particular has a control input for a combined carrier frequency and phase modulation signal.

If the power control loop mentioned is used, it can be designed in an advantageous embodiment for logarithmic detection and processing of the output stage output power. The amplitude signal generator stage is then also for logarithmic processing Arαplitudenmodulationssignal formed, or it is followed by a converter stage for converting a linear m eme logarithmic output characteristic. This converter stage can be formed in particular from a D / A Wanoler and an amplifier with a logarithmic characteristic connected downstream of it.

Advantages and advantages of the invention result from the subclaims and the following description of preferred exemplary embodiments with reference to the figures. Of these show:

1 shows a schematic diagram of a transmission stage according to a first embodiment of the invention,

Fig. 2 eme schematic diagram of a transmission stage according to a second embodiment and

Fig. 3 em functional block diagram of a third, derived from the second embodiment (including the digital processing section).

1 shows, in the form of a schematic diagram, how, according to a first embodiment of the invention, digital frequency / phase format and separate digital amplitude information for obtaining a transmission signal for supply to an antenna are processed separately. The digital frequency / phase format is fed to a digital frequency modulator, the output signal of which controls a voltage-controlled oscillator VCO, the (frequency or phase modulated) output signal of which is fed as a transmission frequency signal via a first input to an output stage. The digital amplitude information arrives at the input of a digital / analog converter, at the output of which it is available as analog amplitude information, which is fed to a second input of the output stage (for example for controlling the supply voltage), thus bringing it together the frequency / phase format and the amplitude information for a QAM transmit signal.

FIG. 2 shows the second embodiment modified compared to the second embodiment, which is distinguished by a different type of control of the output stage. On the one hand, the output stage is preceded here by a preamplifier stage, which is referred to in the figure as "power control" and which outputs the output signal of the voltage-controlled oscillator VCO via a first input and the output signal of the digital / analog

Converter, i.e. the analog amplitude information are supplied via a second input. The provision of this additional stage enables a simpler design of the actual output stage. Furthermore, the input of the pre-amplifier stage is via a suitable detector circuit

Detection of the transmission output power with the output of the transmission output stage m fed back in the form of a power control loop. In this way, operation of the output stage in an impermissible range, in particular oversteer, is avoided.

3 shows a transmission arrangement 1 of a mobile radio terminal, which is supplied with an encoded data bit stream SIG as an input signal from the baseband (not shown) and outputs the transmission signal STX to a combined transmission / reception antenna 3.

The input signal SIG first arrives at the input of a modulation signal processor 5, the core of which is a table memory 5a for storing a tabular assignment between sections of the data bit stream (symbols) and

Phase-amplitude value pairs of a modulation signal. Separate frequency / phase modulation signals PM and amplitude modulation signals AM are available at the output of the table memory 5a addressed with the data bit stream. The frequency / phase modulation signal PM forms the input signal of a frequency synthesis circuit 7. The frequency synthesis circuit 7 has the basic structure of a PLL synthesizer, which can be set extremely remotely and precisely via the digital input signal PM. At its core is a commercially available DDS (Direct Digital Synthesizmg) circuit 7a, at whose add value input the frequency phase modulation signal PM is present and which is connected via a clock input to a clock form circuit 7b, via which a clock signal CLK is supplied. The latter in turn is connected on the input side to the output of a voltage-controlled oscillator 7c, the output signal thereof

OSC also forms the output signal of the frequency synthesis circuit 7. The output of DDS circuit 7a, abuts the em Syn ^¬ synthesis signal SYN is connected to a first input of a phase comparing circuit 7d, 7e on the other input a reference oscillator with a reference signal REF supplied is. The output of the phase comparator circuit 7d, at which an (analog) tuning signal TUN is available, is connected via a low-pass filter 7f to a control input of the voltage-controlled oscillator 7c.

The reference oscillator 7e in the form of a quartz oscillator supplies a reference signal with a constant frequency, the phase position of which is compared to that of the synthesis signal SYN from the DDS circuit 7a. The tuning signal TUN thus reflects the result of this comparison, so that (after the low-pass filtering) the control voltage reflecting the comparison result is also supplied to the voltage-controlled oscillator. In the present embodiment it is assumed that the output signal OSC is sinusoidal and serves directly as a transmission frequency signal; in the case of the formation of the voltage-controlled oscillator 7c for the output of a rectangular pulse signal, the clock shaping circuit 7b would be dispensable. As a result of the effect of the PLL loop implemented in the frequency synthesis circuit 7, the transmission frequency signal OSC is phase-locked, but is connected to the reference signal REF with a frequency that can be set via the DDS circuit 7a. The digital amplitude modulation signal AM is first a D / A converter 9 is ready for conversion logaπthmiertes m em analog Amplitu ^¬ denmodulationssignal and then supplied to a strong Klemsignalver- 11 with a logarithmic characteristic, em at the output amplitude modulation signal LAM. The signal LAM is fed to a control input of a power control stage 13, whose power-controlled output signal is fed to the transmission output stage 15 and, after amplification m, forms the transmission signal STX. Em part of the end signal STX is diverted (via a directional coupler not shown) to a power detector 17 whose output signal together with the signal LDS LAM to Steue ^¬ tion of the transmission power control stage 13 is used. In the transmission power control stage 13, therefore, on the one hand, a merging of the phase and amplitude modulation branch into a phase modulation with a non-constant envelope curve and also a power control of the transmission output stage are realized.

The embodiment of the invention is not limited to the described embodiments, but is also possible in m different combinations as well as in a multitude of modifications which are within the scope of professional action. Thus, in particular in the modulation signal processor of the transmission arrangement, instead of the table memory, a calculation unit for real-time calculation of the separate frequency / phase and amplitude modulation signals can be used, which accesses a calculation algorithm stored in an assigned program memory.

Claims

claims

1. modulation circuit (1) directly to produce a simultaneously pha ^¬ transmitter and amplitude modulated RF signal, in particular a QAM RF signal with a digital phase modulator stage (7) and one of said downstream output stage (15), said first via an input or connected to the output of the phase modulator stage via a power control stage (13)

The digital amplitude signal generator stage (5, 13), which is separate from the phase modulator stage and is connected at least indirectly on the output side to a second input of the output stage or the power control stage.

2. Modulation circuit according to claim 1, so that the digital amplitude signal generation stage (5, 13) is connected via a D / A converter (9) to an analog input of the power control stage (13).

3. Modulation circuit according to claim 1 or 2, so that the second input of the power control stage (13) is additionally connected to the output of the output stage (15) via a power control loop.

4. Modulation circuit according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the digital phase modulator stage (7) and the digital amplitude signal generator stage (5, 13) work as a polar modulator on the basis of m a signal processor stage (5) separately generated phase and amplitude signal data (PM, AM).

5. Modulation circuit according to claim 4, characterized in that the signal processor stage (5) has an assignment memory (5a) for the table-like storage of an assignment rule of an input data bit stream (SIG) to phase amplitude value pairs (PM, AM) of modulation information.

6. Modulation circuit according to claim 4, d a d u r c h g e k e n n z e i c h n e t that the signal processor stage eme calculation unit for real-time calculation of phase-amplitude value pairs from an incoming data bit stream based on an m stored algorithm associated program memory.

7. Modulation circuit according to one of the preceding claims, so that the phase modulator stage (7) has a voltage-controlled oscillator (7c) which is controlled directly or indirectly by a digital phase modulation signal (PM).

8. Modulation circuit according to one of claims 1 to 6, that the phase modulator stage has a frequency synthesis circuit (7a) which in particular has a control input for a combined carrier frequency and phase modulation signal (PM).

9. Modulation circuit according to one of claims 3 to 8, characterized in that the power control loop for logarithmic detection and processing of the output stage output power and the amplitude signal generator stage (5, 13) is designed for logarithmic processing of an amplitude signal or the amplitude signal generator stage eme converter stage (9, 11) for converting a linear m eme logarithmic output characteristic.

10. modulation circuit according to claim 9, d a d u r c h g e k e n n z e i c h n e t that the converter stage has a D / A converter (9) with a downstream logarithmic amplifier (11).