EP2070189A1

EP2070189A1 - Radio receiver

Info

Publication number: EP2070189A1
Application number: EP07802571A
Authority: EP
Inventors: Gerhard Kottschlag; Jens Passoke
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2006-09-25
Filing date: 2007-08-10
Publication date: 2009-06-17
Also published as: DE102006045160A1; RU2009115443A; JP2010504713A; US20100015940A1; WO2008037539A1; CN101517889A; CN101517889B

Abstract

The invention relates to a radio receiver (200) in which the received signal is processed in parallel in at least two paths. A first mixed oscillator signal is above the centre of the channel in one path and a second mixed oscillator signal is beneath the centre of the channel in a second path. Furthermore, spectral components can be filtered out by means of filters and the signals can then be processed and/or combined in a suitable manner.

Description

description

radio receiver

Technical area

The invention relates to a radio receiver.

State of the art

In radio receivers according to the prior art, various concepts are used to extract the desired radio signal from the reception spectrum. In particular, in receivers with digital signal processing various subsequent concepts are widely used.

The high intermediate frequency (IF) heterodyne receiver (e.g., JP 2006 174326). This concept has the advantage that it is robust against disturbing reception of the image frequency and in this respect many filter types, frequencies and hand widths are available. The disadvantage, however, is that the relative bandwidth of the IF filter must be designed very narrow and therefore can not be integrated into standard semiconductor processes, which then high component costs incurred.

Furthermore, the heterodyne receiver with low intermediate frequency is known (for example DE 36 18 782 A1). It has the advantages that the IF filter has a large relative bandwidth and, with the low IF frequency, allows integration even in standard semiconductor processes, which can reduce component costs.

The disadvantage of this is the sensitivity to strong signals on the image frequency, since useful and image frequency are in the same frequency range and filtering in front of the mixer is hardly possible. Furthermore, heterodyne receivers with an intermediate frequency of OHz are known, which are sometimes referred to as zero-IF-concept and subsequently also as direct heterodyne receivers or direct mix. These have the advantages that due to the concept no image frequency is available and the IF filter can be integrated as a low-pass filter in standard semiconductor processes. The disadvantage here, however, that signal components are disturbed in the middle of the channel, as they fall in the mixture to the frequency OHz and would be fed as DC voltage to the subsequent stages. The DC correction measures often required in these concepts all affect low IF frequency components, thereby preventing undistorted processing of those spectral components of the received signal transmitted close to the channel center frequency.

Presentation of the invention, object, solution, advantages

The object of the invention is to provide a radio receiver, which is less prone to interference and can be constructed as simply and inexpensively.

The object is achieved by a radio receiver in which the received signal is processed in parallel in at least two paths, wherein at a path a first local oscillator signal is an amount above the channel center and at a second path a second local oscillator signal is below the channel center Furthermore, spectral components can be filtered out by means of filters and then the signals are processed and / or combined in a suitable manner. This concept is referred to below as a segmented mixture or segmenting heterodyne receiver.

It is advantageous if, furthermore, the signal components of the output signals of the mixers or signals derived therefrom can be digitized by means of analog-digital converters. It is also expedient if the individual stages, such as mixers, analog-to-digital converters and / or filters, can be integrated into a semiconductor. This can advantageously be created a cost-effective implementation.

It is particularly expedient if the processing of the signals takes place in parallel in at least two paths. As a result, a preferably simultaneous processing can be achieved.

It is also expedient if the processing of a plurality of signals takes place in only one or at least one time-multiplexed path. Accordingly, it is advantageous if the analog-to-digital conversion takes place with time offset in the time division multiplex.

Furthermore, it is advantageous if a frequency offset of the local oscillator and / or the filter cutoff frequencies of the bandpasses at the mixer outputs can be varied as a function of the channel raster, the actual signal bandwidth and / or the (interference) signals in the adjacent channels.

It is also expedient if two separate voltage-controlled oscillators (VCO) are used to generate the two oscillator frequencies, which are preferably connected to a common reference frequency by two phase-locked loops (PLL).

In a further exemplary embodiment of the invention, it is expedient for a voltage-controlled oscillator (VCO) to be operated on one of the two mixer drive frequencies or a multiple thereof to generate the two oscillator frequencies, and the second mixer drive frequency to be obtained by mixing this signal with 2 ^* Δ is, or 2n ^* Δ in the event that the division of the oscillator signals prior to their down-division with a division factor n is carried out on the mixer drive frequencies.

In addition, it is particularly advantageous at low reception frequencies to first mix the received signal to an intermediate frequency, preferably far above the reception frequency, and then to add the segmented mixture only in further processing stages in the manner according to the invention undergo. It may be advantageous to perform the first mixing process with a variable frequency, which is generated for example by a VCO, the second mixing process, however, not with another VCO, but with a fixed second mixing frequency.

Advantageous developments are described in the subclaims.

Brief description of the drawings

The invention will be explained in more detail on the basis of an embodiment with reference to the drawings. Show it:

Fig. 1 is a schematic representation of received and interference signals for different reception concepts; and

Fig. 2 is a schematic representation of a radio receiver according to the invention.

Preferred embodiment of the invention

FIG. 1 with the subfigures 1 a to 1 e shows two reception concepts according to the prior art and illustrates the reception concept according to the invention schematically.

In Figure 1a, the composition of the received signal is sketched for illustration. In this case, a useful signal 10 of the channel bandwidth BB is flanked by a plurality of interference signals S1, S2, S3, S4. The subdivision A, B, C, D in the useful signal is used later to explain the receiving mechanisms, these blocks include, for example, spectral components of a common useful signal.

FIG. 1b shows a representation for heterodyne receivers with a low intermediate frequency. If in a heterodyne receiver a mixing oscillator is used, whose frequency is possibly well outside the receiving channel, the received signal is converted by the mixing process in a different frequency range. The signals applied to the image frequency are also transferred to the same frequency range. Since it is no longer possible to separate the useful signal from the image frequency signal, the reception capability on the image frequency must already be adequately suppressed by suitable measures, for example by prefiltering by means of a bandpass filter BPF, or by using a mirror frequency-suppressing mixer increases the interference immunity. However, the suppression capability of such mixers is typically significantly limited by the characteristics of the technology used. For concepts with a low IF for radio reception, both of the measures described above, even in combination, do not exhibit sufficient interference immunity in order to meet the customer expectations demanded by the good interference behavior of conventional receivers with reasonable effort.

FIG. 1 c shows a representation of the so-called direct superimposed receiver. When the receive band is mixed with an oscillator signal in the middle of the receive channel, it is called a direct-mix or zero-IF concept, which means that the center frequency of the IF band drops to 0 Hz. Since positive and negative frequencies do not differ with respect to their frequency, the signal components C and D fall above the oscillator frequency exactly on the signal components B and A, which were below the oscillator frequency in the receiving channel. When using an IQ mixer which mixes the received signal in a first mixer cell on the one hand with the local oscillator signal, in a second mixer cell the same received signal with the shifted by 90 ° Mischoszillatorsignal, the two sub-spectra below or above the Oscillator frequency recovered and merged to the original useful signal. In principle, the direct heterodyne receiver exhibits the same image frequency problems as a low intermediate frequency heterodyne receiver. However, here is the mirror band part of the Nutzkanals (A and B are the mirror to D and C and vice versa). Thus, it is impossible that a high-level interference signal is superimposed on a weak useful signal, the mirror level is always just as large as the unsmoothed signal component, and thus about 3OdB to 4OdB mirror rejection are usually sufficient here. The problem with the direct heterodyne receiver is the frequency ranges which are close to the frequency OHz, indicated by the dividing line 20. These spectral components of the blocks B and C, which are originally located in the middle of the channel of the useful signal, can be impaired during further processing, for example by Circuit parts of the receiver to compensate for a DC offset by signal components in the middle of the channel at the transition point between the blocks B and C or temperature drift of the receiver stages.

FIGS. 1 d and 1 e show the conditions occurring in the case of the segmented mixture according to the invention, in this case segmented direct mixture. The radio receiver according to the invention uses two IQ mixers with then four mixing cells, so that the received signal is mixed with four different oscillator signals. Two frequencies are used, each with two phase angles shifted by 90 °. In the example shown, the two are shifted by +1/8 or -1/8 of the bandwidth (BB) of the user channel from the channel center frequency. The advantages can be seen from the graph: the IQ mixer controlled by the lower-frequency signal, see FIG. 1d, can output the segments A and C undisturbed, they are extracted by a subsequent bandpass filter BPF. The block B is affected by its frequency position near OHz, the block D possibly disturbed by a strong interference signal S1 on the image frequency.

Exactly these missing blocks B and D are provided undisturbed by the other IQ mixer according to FIG. 1e. Here, the areas A and C are affected by the disturbance scenarios described above.

Segments A, B, C, and D are not to be understood as sharply demarcated blocks in the practice of the invention, but may be readily overlapped with a suitable weighting function, as indicated by the sloping filter edges of the graph. The radio receiver according to the invention is based on a heterodyne receiver or direct superimposed receiver, which is designed in several stages double or multiple and modified as described below. The received signal is typically processed in parallel in at least two paths, with the local oscillator signal of the first path or the first local oscillator signal being a suitable fixed amount above the channel center and the local oscillator signal or the second local oscillator signal being the same fixed magnitude below the channel Channel center is located. The offset is usually less than half the channel bandwidth, preferably about 1/8 Kanal- hand width. From the output signals of the two mixing stages at least the spectral components are filtered out, as for example by means of bandpass filters eliminated, which would be affected by DC correction measures. Preferably, this filtering also removes further spectral components that could be affected by the superposition of image frequency reception. The remaining signal components of the different paths are then reassembled to give an undisturbed image of the complete signal spectrum in the receiving channel. Preferably, prior to the composition of the signal components, the optionally filtered output signals of the mixers are first digitized, so that the combining and possibly existing filtering can take place in the digital part. When using only one path or part of a path, for example, a single analog-to-digital converter, the various signal components in the respective stages can be processed in time-division multiplexing.

Despite the increased number of processing blocks, such as doubling the number of, for example, IQ mixing, bandpass filters, A / D converters, the radio receiver device of the present invention can be cost effective since the required levels can be integrated into standard semiconductor technologies and possibly only low cost external ones Components are additionally required.

The generation of the oscillator signals fo + Δ and fo-Δ can preferably be carried out from a single, for example, connected to a phase-locked loop, voltage controlled oscillator VCO. From the VCO is directly or by division a mixer drive signal on the Nutzkanal-center frequency which is mixed in an IQ mixer at the offset frequency Δ (preferably Δ = 1/8 ^* BB). At the outputs of a summing or subtracting stage of the mixer are the two mixer drive signals f _o + Δ and f _o -Δ. From these signals, the two offset by 90 ° signals are derived, which are additionally required for the control of the mixer cells in the signal path.

The radio receiver according to the invention has the advantage that all significant components can be integrated in standard semiconductor technologies. As a result, expensive external filters can possibly be avoided.

In addition, it may preferably be the case that no interference due to DC effects and DC compensation circuits occur because the affected spectral components can be discarded or substituted by the signal of the other path. In addition, the 1 / f noise is lowered because the most affected low-frequency signal components of the baseband are filtered out as described and therefore no longer go into the output signal.

It is also advantageous that no disturbances occur due to image frequency reception since only those signal components are used whose image frequency lies in the useful channel.

It is likewise advantageous for the mixer cell in the oscillator path to generate weak interference signals at the input frequency and the respectively undesired mixing frequency, but the frequency position of these signals ensures that no strong interfering signals from adjacent channels are mixed into the useful signal.

FIG. 2 shows a schematic block diagram of a radio receiver 200 according to the invention. The received signal of an antenna 201 is filtered by means of a downstream filter 202 and amplified by means of amplifier 203 connected downstream to the inputs 211a, 221a, 231a and 241a of four mixer cells 21 1, 221, 231, 241 passed. The output signals of the mixers 211, 221, 231, 241 are preferably band-pass filtered by means of the downstream filters 212, 222, 232, 242, and then by means of the analogue Digital converter 213, 223, 233, 243 digitized and a digital signal processor DSP 251 supplied. In the digital signal processor 251, the four processed signals of the mixers are brought together in a suitable manner, then demodulated and further processed in a known manner.

The mixer drive signals for the mixer cells 211, 221, 231, 241 are generated from a voltage-controlled oscillator VCO 261 and a further oscillator 263. The voltage controlled oscillator VCO 261 is controlled by a prior art phase-locked loop (PLL), not shown. The second oscillator 263 provides a contrast, lower frequency signal fi, as the output signal f ₀ of the voltage-controlled oscillator VCO 261. Instead of the second oscillator 263 and a divided down reference signal of the receiving system may optionally be fed, wherein the dividing factor can be changeable. This is particularly advantageous in order to be able to set or tune a suitable frequency offset. The frequency of this signal results from the desired frequency offset Δ between the mixer drive signal of an IQ mixing path and the channel center frequency, eg 1/8 ^* BB, with BB equal to the bandwidth of the receive channel, and the split ratios in the signal chain between the oscillator and the mixer cells.

In Fig. 2, the divider 264 enters, so that U = 4 ^* Δ results in this case. The divider 264 allows in a known manner the generation of two output signals with a phase shift of 90 °, these signals control two mixer cells 271, 281, in which the divided by the divider V, see block 262, VCO signal f ₀ by ± Δ is offset. By the offset by 90 ° control of the two mixer cells 271, 281 is effected in a known manner that at the outputs of the summation 272 and subtractor 282 at one output the signal fo / V - Δ and at the other output the signal fo / V + Δ is present. In the phase shifters 273 and 283, the signals required to drive the mixer cells 211, 221, 231, 241 are generated with a 90 ° phase offset. Alternatively, the out of phase signals may also be generated by further divider stages, which may be similar to stage 264. The division factor would then be taken into account in the design of the oscillator signal chain.

In a modified embodiment, instead of parallel processing over multiple paths, processing is performed in a single path in time-division multiplexing. For example, this results in less wiring effort.

Accordingly, in a further embodiment, the analog-to-digital conversion can not be performed with four separate analog-to-digital converters, but with an analog-to-digital converter in time division multiplex.

According to a further development of the invention, the frequency offset of the local oscillator and / or the filter cutoff frequencies of the bandpasses at the mixer outputs can be dependent on the channel raster, the actual signal bandwidth and / or the (interference) signals (for example level and / or bandwidth). be varied in the neighboring channels.

Furthermore, it is expedient according to the invention in a further exemplary embodiment if two separate voltage-controlled oscillators (VCO) are used to generate the two oscillator frequencies, which are preferably connected to a common reference frequency by two phase-locked loops (PLL).

Also, for generating the two oscillator frequencies, a voltage-controlled oscillator VCO can be operated on one of the two mixer drive frequencies or a multiple thereof, the derivative of the second mixer drive frequency in this case takes place by mixing with 2 ^* Δ or 2n ^* Δ in the case of splitting the oscillator signals Downsizing, by means of the division factor n, the mixer drive frequencies are generated.

Furthermore, in another embodiment, the generation of the offset by 90 ° mixer drive signals by divider stages at the outputs of Summing or subtracting stages 272, 282 are made. The division ratio can be chosen so high that the remaining at the outputs of the stages 272, 282 noise components are sufficiently lowered and thereby a sufficient immunity to interference can be achieved.

Especially at low reception frequencies, it should be noted that the harmonics of the local oscillator signals also contribute to the mixture and can lead to secondary reception points at integer multiples of the reception frequency. In a further embodiment variant according to the invention, this effect is counteracted by first mixing the received signal using a VCO to a fixed intermediate frequency, preferably far above the receiving frequency, where the unwanted mixing products of the harmonics and image frequency reception can be eliminated with simple filter measures, and Only then, in further processing stages, the above-described segmented mixture takes place at 0 Hz. The second mixture does not require a second variable frequency oscillator corresponding to block 261, since the intermediate frequency remains constant, a fixed output frequency oscillator can be used and mixed with the signal of oscillator 263 in the manner previously described.

In addition, an adjustment of the oscillator mixer can be done by measuring the Störträger-level. In the reception path, the mixer inputs are switched off, so that no received signal is passed through the mixing stages. Now, only the oscillator residues and interference lines due to mirror carrier and VCO throughput are present at the mixer outputs. The strength of these signals can be detected and minimized by balancing the signal levels.

Furthermore, according to a further inventive concept, a compensation of the oscillator-mixer imbalance can be made. The spurious signals resulting from residues of the mirror carrier and / or VCO throughput are preferably eliminated in the digital part by antiphase addition.

Claims

claims

1. radio receiver (200) with at least one mixing stage and a

Mischoszillator, characterized in that the frequency of a first local oscillator signal by an amount above the channel center of the receiving or an intermediate frequency and that of a second local oscillator signal is below the channel center by an amount, and further by means of filtering spectral components are ausfilterbar and then the further processed signals be merged again.

2. Radio receiver according to claim 1, characterized in that at least some stages of the signal path are executed several times and in which the received signal in the stages can be processed in parallel using the various local oscillator signals.

3. Radio receiver according to claim 1 or 2, characterized in that the received signal is processed using the different local oscillator signals in time division multiplex.

4. Radio receiver according to at least one of the preceding claims, characterized in that the output signals of the

Mixer (21 1, 221, 231, 241) or signals derived therefrom by means of analog-to-digital converters (213,223,233,243) are digitized.

5. Radio receiver according to at least one of the preceding claims, characterized in that the individual stages, such as

Mixer (21 1, 221, 231, 241), analog-to-digital converter

(213,223,233,243) and / or filters (212,222,232, 242) are integrated in a semiconductor device.

6. Radio receiver according to at least one of the preceding claims, characterized in that the analog-digital conversion is time-shifted in time division multiplex.

7. Radio receiver according to at least one of the preceding claims, characterized in that the frequency offset of the local oscillator signals and / or the filter cutoff frequencies of the band passes at the mixer outputs in dependence of the channel grid, the actual signal bandwidth and / or the (interference) signals in the adjacent channels are variable.

8. Radio receiver according to at least one of the preceding claims, characterized in that the two local oscillator signals are obtained from the mixture of two oscillators, wherein an oscillator is operated at the center of the channel receiving or an intermediate frequency or an integer multiple of these frequencies.

9. Radio receiver according to at least one of claims 1 to 7, character- ized in that two separate voltage controlled oscillators (VCO) are used to generate the two oscillator frequencies, which are preferably connected by two phase-locked loops (PLL) to a common reference frequency.

10. Radio receiver according to at least one of claims 1 to 7, characterized in that for generating the two oscillator frequencies by a voltage-controlled oscillator VCO on one of the two mixer drive frequencies or a Vielfachen thereof, a derivative of the second mixer drive frequency by mixing with 2 ^* Δ or 2n ^* Δ when dividing the oscillator signals prior to their down-division, with a division factor n, to the mixer drive frequencies vornehmbar.

1. Radio receiver according to at least one of the preceding claims, characterized in that the received signal is previously mixed and filtered to an intermediate frequency.