CH676404A5 - - Google Patents

Description

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CH676 404 A5

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description

The present invention relates to a method for reconstructing lost DC useful components of IF signals in a direct-conversion version receiver according to the preamble of patent claim 1 or 2 and to a receiver for performing the method according to the preamble of patent claim 3. 4 or 5.

in a direct conversion receiver, the received, angle-modulated RF input signal, after having been fed to an input filter and an RF preamplifier, is mixed with a LO signal generated in a local oscillator (LO). Since the LO signal has approximately the same frequency as the RF input signal, an intermediate frequency signal (IF) is generated after the mixing, which is in the low-frequency range (NF). From a mathematical point of view, the mixture sometimes produces negative frequencies, which in practice cannot be distinguished from the positive ones. Likewise, direct voltage components (DC useful components) can also be generated. In order to maintain full information, it is necessary for direct conversion receivers to form two IF signals shifted by 90 ° to each other. For this purpose there are two mixing stages, to which the RF signal and the LO signal are applied, whereby either the RF or LO signal applied to one mixing stage is phase-shifted by 90 ° compared to the corresponding signal applied to the other mixing stage . One mixer stage generates a first IF signal and the other mixer stage generates a second IF signal which is 90 ° out of phase with the first IF signal. Each of the IF signals (I, Q) formed in this way is then fed to, for example, an analog, digital or mixed low-pass filter, each with a following IF amplifier stage, and then demodulated in a demodulator. Because the intermediate frequency in direct conversion receivers is in the LF range, the demodulator can be set up with integrated circuit technology. The filtered IF signals (I, Q) are converted in a preferred embodiment, as indicated for example in European Patent 0 180 339, into analog digital converters into digital signals and digitally processed for demodulation. Digital signal processors (DSP) have proven to be useful circuits. Incidentally, it should be mentioned that it is also possible to integrate the entire ZF part. The required dynamic range, power consumption and the price of the receiver primarily determine the technology to be used.

As already mentioned, the IF signals in direct-conversion receivers can contain direct voltage components (DC useful components). In order to process the full information in the IF part of the receiver, the IF amplifiers would have to have a transmission range that extends down to zero Hertz. This is hardly feasible, since DC offset voltages occur in amplifiers and mixer stages, which can be considerably larger than the two IF signals mentioned. This would overdrive the IF stages and create unacceptable distortion during demodulation. This can be prevented, for example, by the AC coupling of the IF stages separating the DC components from the IF signals. As a result, the DC offset voltages, but undesirably also the above-mentioned useful DC components of the two IF signals, are lost as desired. Therefore, in certain situations, distortions can arise in the demodulation. Although these distortions are of less magnitude, they are still annoying.

European patent 0 255 175 mentions the occurrence of these distortions and describes a demodulation method for demodulating an angle-coded signal in which, in order to prevent such distortions, a control signal is formed from the IF signals supplied to the demodulator, which control signal is used as a correction signal for the demodulated NF- Signal acts.

It is the object of the present invention to propose a method for reconstructing the useful DC components in the IF signals which have been lost as a result of AC coupling and which works independently of the demodulator.

Another task is to create suitable recipients for performing the method.

The first object is achieved according to the features listed in the characterizing part of claim 1 or 2. Receivers according to the invention have means for reconstructing the lost useful DC components, as characterized by the features of claims 3, 4 or 5.

The method disclosed in this document and the disclosed embodiment variants of receivers for performing the method are all characterized in that the individual method steps can be carried out in a self-contained module without any correction or control signals at other receiver stages, in particular the demodulator or act on the NF part.

The module includes the reconstruction means mentioned. These can have a program-controlled, digital signal processor or can be constructed from individual analog and / or digital function stages.

Because the module works independently of other receiver levels, it is very versatile.

Fluctuations in amplitude of the input signal (fading) have practically no effect, provided the fluctuations are the same for the two IF signals shifted by 90 °. The reconstruction module is suitable for both radio and cable transmission links.

The invention is described in more detail below using figures, for example. Show it:

1 shows the block diagram of a direct conversion receiver,

Fig. 2 is a block diagram of the means for Rekon5

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structure lost DC useful components in the ZF-Si signals,

3 shows a coordinate representation for explaining the function of the reconstruction means and

FIG. 4 shows a block diagram according to FIG. 2 with expanded reconstruction means.

1 shows the block diagram of a direct conversion receiver, in which the method according to the invention is used to reconstruct the useful DC components of the IF signals (I, Q) lost, for example, due to AC coupling in the IF part. An RF input signal is received with antenna 1, filtered in an input filter 2 and amplified in a preamplifier 3. A local oscillator 4 generates a local oscillator signal, hereinafter referred to as LO signal, which has approximately the same frequency as the RF input signal received by antenna 1. The LO signal is fed to two mixer stages 6, 7, a first mixer stage 6 directly and a second mixer stage 7 via a phase shift element 5. The two mixer stages 6, 7 also each receive the RF signal amplified by the preamplifier 3. Each of the mixing stages 6, 7 generates an IF signal at its output, which is in the low-frequency range because of the approximate equality of the frequency of the RF input signal and the LO signal. Each of the IF signals is low-pass filtered in a low-pass filter 8, 9 and amplified in a respective IF amplifier 10, 11. An IF signal I is present at the output of the first IF amplifier 10 and an IF signal Q which is 90 ° out of phase with the signal I is present at the output of the second IF amplifier 11. As already explained in the introduction to the description, the two IF signals I, Q can each contain a direct voltage component, hereinafter referred to as DC useful component, in direct conversion receivers. As a result of high-pass filters or AC couplings, for example, this useful DC component together with DC offset voltages in each of the IF signals 1, Q has been removed. Due to the lack of a possibly available DC useful component, the IF signals I, Q contain errors, which leads to distortions during demodulation. The two IF signals I and Q, which are subject to errors, are fed to a means 12 for the reconstruction of lost DC useful components. With these reconstruction means, the method according to the invention is carried out on the two signals I and Q and the two corrected IF signals Ik and Qk or the two normalized corrected signals In and Qn are generated, which are forwarded to a demodulator 13 for generating the LF signal will.

FIG. 2 shows the block diagram of a first embodiment of the reconstruction means 12, on the basis of which the method according to the invention for reconstructing the separated DC useful components in the IF signals I and Q is explained. The reconstruction element 12 has two inputs to which the IF signals I and Q are fed and two outputs at which the corrected IF signals Ik and Qk are reconstructed with each

DC useful part. Each of the signals I, Q, which has errors, is supplied to a subtractor 20, 21, to which correction signals Ei or Eq are also present and influence the signals I, Q in such a way that a corrected one is provided at the output of each of the subtractors 20, 21 mentioned IF signals Ik or Qk are present. The correction signals Ej, Eq can be interpreted as manipulated variables of a control loop, which come about as described below. The corrected output signals Ik, Qk are fed to a first stage 22, in which the square of each of the signals is formed, the two squared signals are added, and a further signal R, which corresponds to the root and is present at the output, is formed from the sum. The further signal R is then fed to a high-pass filter 23 and connected to a multiplier 24, 25 as a high-pass filtered signal EX. In a multiplier 24, the corrected signal Qk is multiplied by the high-pass filtered signal EX and supplied to a first integration stage 26 as the output variable EXq. The corrected signal Ik is multiplied in the other multiplier 25 by the high-pass filtered signal EX and fed as a variable EXi to a second integration stage 27. The output signal of the first integration stage 26 is the correction signal Eq, which is present as a steep variable at one subtractor 20 and the output signal of the second integration stage 27 is the correction signal Ei, which is present as a steep variable at the other subtractor 21.

In FIG. 3, attempts have been made to clearly show the previously described method in an XY representation. For better comprehensibility, it is assumed below that the correction signals Ei, Eq are separated from the subtracting stages 20, 21. The IF signals, which are 90 ° out of phase with each other, span a vector r. Purely sinusoidal or cosine-shaped IF signals I ', Q' form a vector f which rotates at a uniform rotational speed around the center Z 'of the coordinate system. If the IF signals have a useful DC component after mixing, this is shown in the illustration by the fact that the rotational speed of the vector f is no longer constant. For example, AC coupling removes DC components in the IF signals. This is expressed in the graphic representation as a linear displacement A of the coordinate axis I 'to the coordinate axis Ik and as a linear displacement B of the coordinate axis Q' to the coordinate axis Qk. The intersection Z of the latter two coordinate axes is the new center, around which the vector r rotates as a result of the separation of the DC useful components from the IF signals I, Q, which are now subject to errors. The amount R of the vector r changes continuously. In the aforementioned stage 22, nothing else is done other than continuously calculating the amount R of this latter vector. Exactly this happens according to the Pythagorean theorem, corresponding to that indicated in Figures 22 and 22 at level 22

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Formula. In the event that the reconstruction means 12 comprise a program-controlled, digital signal processor, the root extraction becomes somewhat complex. Appropriate approximation formulas for forming the amount of the circle radius, for example

R = HyMQyU max CllKl, tQrt)

are therefore used. The formula given above means that the instantaneous values of the amounts of the Ik and Ck signals plus the larger of the instantaneous amounts of the two signals are continuously added and the sum is halved. The small error that arises does not noticeably affect the reconstruction. As already said, the amount R of the vector r changes continuously as soon as the origin of the coordinate system is shifted. This change in radius is used as a criterion for the size of the displacement. In order to obtain a signal for the change of R from the signal R, the latter is fed to a high pass filter 23, which separates the constant part from the signal R and forms the high pass filtered signal EX. If this latter signal is multiplied by Ik or Qk and the product is integrated in the integration stages 26 and 27, the two control signals E | or Eq, which shift the center Z towards the original center Z '.

FIG. 4 shows a block diagram with reconstruction means expanded compared to FIG. 2. So that the control circuit always functions correctly, regardless of the input level, i.e. To increase the dynamic range, the corrected signals Ik, Qk are normalized in this exemplary embodiment by dividing each of these signals by the mean value R of the further signal R in a respective divider stage 30, 31. The normalized, corrected signals In and Qn are present at the output of each of the dividing stages 30, 31 mentioned. The mean value R of the further signal R is obtained by filtering the latter in a low-pass filter 28. The further signal R and the low

pass-filtered signals R are fed to a subtractor 29, which provides a standardized signal EX at its output. The low-pass filter 28 and the subtractor 29 together form a high-pass filter, so that the signal EX just mentioned corresponds in principle to the high-pass filtered signal EX mentioned in FIG. 2.

The method according to the invention can be carried out in differently designed receivers. A first preferred embodiment provides a receiver of the type described in the introduction, in which the reconstruction means 12 comprise a program-controlled, digital signal processor for carrying out the method steps mentioned. A second preferred embodiment provides for the reconstruction method to be carried out in the same program-controlled digital signal processor that has already been used as a demodulator. In a third preferred embodiment variant, the individual method steps for reconstructing the useful DC components in the IF signals are carried out in analog and / or digital function stages formed from discrete and / or integrated components.

Claims (1)

Claims 1. A method for the reconstruction of lost DG useful components of IF signals in a Direct Con version receiver, in which a received angle-modulated RF signal with one LO signal generated in a Lokatos-zillator (4) in two Mixing stages (6, 7) are mixed and two IF signals shifted in phase by 90 ° are formed, whereby each of the IF signals can contain a DC useful component, each of which is in an AC-coupled IF part (8, 9 , 10, 11) is separated, which results in IF signals (I, Q) which have errors, characterized in that a) each of the IF signals (I, Q) which has errors is supplied with a correction signal (Et, Eq) and a corrected signal (Ik, Qk) is generated, b) each of the corrected signals (Ik, Qk) is squared, the signal squares are added and a further signal (R) corresponding to the root is formed from the sum, or the further signal (R) is determined by approximating the above steps , c) the further signal (R) is high-pass filtered and the high-pass filtered signal (EX) is multiplied by each of the corrected signals (Ik, Qk) and d) the product signal (EXi, EXq) for forming the two correction signals (Ei, Eq) is integrated, 2. A method for reconstructing lost DC useful components of IF signals in a direct conversion receiver in which a received angle-modulated RF signal, each with an LO signal generated in an LC oscillator (4), in two mixing stages (6, 7 ) is mixed and two IF signals shifted in phase by 90 ° are formed, each of the IF signals can contain a DC useful component, each of which is in an AC-coupled IF part (8, 9, 10, 11) is separated, resulting in IF signals with errors (I, Q), characterized in that a ') each of the IF signals with errors (I, Q) is supplied with a correction signal (Et, Eq) and a corrected one Signal (Ik, Qk) is generated, b ') each of the corrected signals (Ik, Qk) is squared, the signal squares are added and a further signal (R) corresponding to the root is formed from the sum or the further signal (R) is determined by approximating the above steps becomes, C) the further signal (R) is low-pass filtered, d ') each of the corrected signals (Ik, Qk) is divided by the low-pass filtered signal (R') to form a standardized corrected signal (In, Qn), 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 4th 7 CH676 404A5 e ') the further signal (R) is high-pass filtered, the high-pass filtered signal (EX) is multiplied by each of the standardized corrected signals (In, Qn) and f) each the product signal (EXi, EXq) to form the two correction signals (Et, Eq) is integrated. 3. Receiver for performing the method according to claim 1 or 2 with an RF part (1, 2, 3), a local oscillator (4), two mixing stages (6, 7), an IF part (8,9,10, 11) with two channels for filtering and amplifying the IF signals generated in the mixing stages (6, 7) and a demodulator (13), the IF signals (8, 9, 10, 11) present after the IF part (8, 9, 10, 11) I, Q) are subject to errors as a result of the DC useful component separated by AC coupling, characterized in that reconstruction means (12) in the form of a program-controlled digital signal processor for carrying out the individual method steps (a, b, c, d) or ( a ', b', d ', e', f) for generating corrected IF signals (Ik, Qk) or standardized corrected IF signals (In, Qn) are present. 4. Receiver for performing the method according to claim 1 or 2 with an RF part (1, 2, 3), a local oscillator (4), two mixing stages (6, 7), an IF part (8,9,10, 11) with two channels for filtering and amplifying the IF signals generated in the mixing stages and a demodulator (13), the IF signals (I, Q) present after the IF part (8, 9, 10, 11) as a result of the DC useful component separated by AC coupling are subject to errors, characterized in that the demodulator (13) is designed as a program-controlled digital signal processor and also for performing the individual method steps (a, b, c, d) or (a ', b ', c', d ', e', f) is intended for generating corrected IF signals (Ik, Qk) or normalized corrected IF signals (In, Qn). 5. Receiver for performing the method according to claim 1 or 2 with an RF part (1, 2, 3), a local oscillator (4), two mixing stages (6, 7), an IF part (8,9,10, 11) with two channels for filtering and amplifying the IF signals generated in the mixing stages and a demodulator (13), the IF signals (I, Q) present after the IF part as a result of the DC useful component separated by AC coupling are characterized by errors, characterized in that the reconstruction means (12) for performing the individual method steps (a, b, c, d) or (a'r b ', c', d ', e', f) corrected to form IF signals (Ik, Qk) or standardized corrected IF signals (In, Qn) analog and / or digital function stages (20, 21, 22, 23, 24, 25, 26, 27) formed from discrete and / or integrated components or (20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 31). 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 5