Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
  • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
  • H04L27/36—Modulator circuits; Transmitter circuits
  • H04L27/362—Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated
  • H04L27/364—Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
  • H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
  • H03D7/18—Modifications of frequency-changers for eliminating image frequencies

Definitions

• the invention relates to frequency transposition devices with a single sideband (also designated by "IQ mixers", according to a name usually used by a person skilled in the art) and in particular the adjustment of the radio frequency emission spectrum, in 5 particularly the image rejection and the rejection of the local oscillator line of these IQ mixers.
• IQ mixers also designated by "IQ mixers"
• the invention finds a particularly advantageous and non-limiting application in the field of mobile telephones incorporating such mixers.
• the useful signal transmitted in this case the voice, which is a low frequency signal, is transposed into a high frequency signal in the IQ mixer using a high frequency signal originating from a local oscillator.
• the output spectrum of the signal from the mixer therefore contains a so-called useful line, corresponding to the useful signal transposed to
• the adjustment consists in adjusting the symmetry of the low frequency input signals from the mixer to compensate for the internal asymmetries of this component which are responsible for the increase in the image and local oscillator lines of the ' output spectrum.
• test signals are used which are respectively delivered at the input of the two channels I and Q of the mixer.
• Each test signal typically has a continuous component and a periodic component (in practice sinusoidal).
• the periodic components of the two test signals are mutually out of phase.
• the adjustment consists, for a fixed value of the frequency of the local oscillator signal, in adjusting the value of the continuous components, the ratio of the amplitudes of the two sinusoidal components as well as the value of the phase shift, in order to minimize the levels of the parasitic lines.
• a conventional method for making this adjustment consists, for each possible local oscillator frequency (each associated with a transmission channel), of carrying out a scan on the input channel I, then on the channel Q, to measure, for the different values of the different parameters of the test signals, the levels obtained for the image and local oscillator lines, and to repeat this operation by refining the scanning steps until obtaining the desired rejection. Parameter values are then obtained, making it possible to obtain very low levels for the image and local oscillator lines.
• this method has the drawback of requiring a very large number of measurements, typically of the order of a few tens to a few hundreds for a local oscillator frequency value, and therefore a very long adjustment time.
• the adjustment is carried out with a nominal supply voltage. It is further verified that at the end of the telephone battery life, the quality of the output spectrum of the mixer always conforms to the desired specifications.
• variations in the supply voltage and / or the temperature in particular can modify, for example, certain characteristics of the transistors forming certain elements of the mixer, and consequently modify its behavior, in particular at level of internal asymmetries. This then results in a mismatch between the adjustment parameters established during the test with the nominal voltage.
• Optimal adjustment of the mixer would then require a new adjustment of the parameters of the test signals in real time. However, such an adjustment in real time, that is to say during a period of locking the telephone on a transmission channel, is completely incompatible with the duration of adjustment currently necessary.
• the efficiency of the current method is all the worse the closer one is to the solution, that is to say the reference values of the parameters making it possible to obtain the desired rejection.
• the efficiency of the current method is all the worse the closer one is to the solution, that is to say the reference values of the parameters making it possible to obtain the desired rejection.
• very low measurement noise tends to "trap" the iterative search algorithm in local minima, thus leading to obtaining reference values (optimal values) for these parameters, different from the values theoretical benchmarks.
• the invention aims to provide a solution to these problems.
• An object of the invention is to provide an adjustment of the output spectrum of such IQ mixers, which requires a very small number of measurements to determine the parameters of the test signals.
• the object of the invention is also to propose a setting which can be implemented in real time in a mobile telephone because of its very short duration.
• the invention also aims to increase the efficiency of the adjustment.
• the invention results in particular from the fact that it has been found that it is possible to correlate the power (that is to say the level) of the image and local oscillator lines of the output spectrum, to the different parameters of the test signals by two mathematical relations of the paraboloid type.
• the invention is remarkable in that the determination of the reference values (optimal values) for the parameters considered, reference values corresponding to theoretically zero levels of these parasitic lines, can be carried out by a numerical calculation. from a reduced number of measurements, typically a few measurement points.
• the invention therefore differs from the prior art, in particular by the fact that the determination of these reference values is carried out here by a numerical computation whereas in the conventional method previously used, this determination is carried out by the only observation of the measured levels of a very large number of points, so as to select the values of the parameters having led to a minimum level.
• the invention thus makes it possible to reduce the duration of the adjustment in a ratio greater than ten, which reduces the cost of the products incorporating such a mixer, since the cost of the test represents a significant percentage of the cost of these products.
• the duration of such an adjustment according to the invention makes it easy to be able, if necessary, to implement such an adjustment in real time during the operation of a mobile telephone.
• the invention therefore proposes a method for adjusting the level of the parasitic lines of the output frequency spectrum of a frequency transposition device with a single sideband, this method comprising: - the delivery at the input of the two channels the frequency transposition device, two configurable and mutually phase-shifted test signals,
• each test signal comprises a continuous component and a periodic time component (for example a sinusoidal component).
• the continuous components of the two test signals constitute first and second parameters respectively, while the ratio of the amplitudes and the relative phase shift of the two periodic time components of the two test signals constitute third and fourth parameters respectively.
• the parasitic lines include an image line and a local oscillator line.
• the first and second parameters are connected at the level of the local oscillator line by a first parabolic relation, while the third and fourth parameters are linked at the level of the image line by a second parabolic relation.
• the reference values of the first and second parameters are then determined by performing only measurements of the level of the local oscillator line, while the reference values of the third and fourth parameters are determined by performing only measurements of the level of the stripe image.
• a first variant of the invention consists in calculating the position of the optimum of the parabolic relation considered by determining the point where the derivative is zero.
• the reference value of each parameter is determined by using at least four different test values of said parameter, so as to obtain at least four corresponding measured values of level.
• the value of the parameter corresponding to a zero derivative of the corresponding parabolic relationship is then calculated from said test values and corresponding level values, this value constituting said reference value for the parameter considered.
• test values used for this variant is equal to four.
• two triplets of consecutive test values can be formed, for example the first, the second and the third on the one hand, and the second, the third and the fourth. on the other hand.
• the difference between the two measured level values corresponding to the extreme test values of each triplet is then advantageously calculated (for example, on the one hand, the difference between the levels corresponding to the first and third test values, and, on the other hand, the difference between the levels corresponding to the fourth and second test values).
• We then make the relationship between this difference and the difference of said two extreme values of the triplet considered in this case, on the one hand, the difference between the third and the first test values and, on the other hand, the difference between the fourth and second test values).
• variants of the invention consist in taking a certain number of measurement points and in solving a linear system of several equations with several unknowns, for example according to the known method known as of Kramer.
• the reference value of each parameter is determined by using only three different test values of said parameter so as to obtain three corresponding measured values of level, and to obtain a linear system of three equations with three unknowns from the corresponding parabolic relation, the three different test values and the three corresponding measured level values. Then said linear system is solved.
• Another variant of the invention makes it possible to determine the respective reference values of the first and second parameters by using only four different pairs of test values for said values.
• first and second parameters so as to obtain four corresponding measured level values and to obtain a first linear system with four equations with four unknowns from the corresponding parabolic relation, from the four pairs of test values and from the four measured level values corresponding.
• the invention also relates to a system for adjusting the level of the parasitic lines of the output frequency spectrum of a frequency transposition device with a single sideband, comprising delivery means for delivering at the input of the two channels of the transposition device. frequency, two configurable and mutually out of phase test signals, means for measuring the level of each of the parasitic lines for test values different from the different parameters of the two test signals, and means for determining reference values for the different parameters to minimize the level of stray lines.
• the means for determining the reference values comprise processing means, for example carried out in software within a microprocessor, capable of performing a numerical calculation from a predetermined number of different test values of said parameters and corresponding measured level values, taking into account two parabolic relationships connecting the level of the two parasitic lines to said parameters.
• the invention also relates to a mobile telephone containing a frequency transposition device and such an adjustment system, so as to allow the implementation of the method according to the invention within the telephone, whether in the factory or else in real time during phone operation.
• FIG. 3 illustrates a correlation according to the invention between the level of the parasitic lines and some of the adjustment parameters
• Figure 4 illustrates a section in the plane Q of the paraboloid of Figure 3;
• FIG. 5 partially illustrates a first variant implementation of the method according to the invention
• FIG. 6 illustrates very schematically an embodiment of an adjustment system according to the invention
• the reference DTF designates a frequency transposition device with a single side band, or mixer IQ, comprising two mixing channels VF1 and VF2 joined by a terminal adder AD connected to the output terminal BS of the mixer.
• the channel VFl comprises a mixer M 1 receiving, on the one hand, the signal TXI present at the input terminal BI of the mixer, and, on the other hand, a signal OLl equal to
• the channel VF2 comprises a mixer M2 receiving, on the one hand, the signal TXQ present at the input BQ of the mixer, and, on the other hand, a signal OL2 equal to LOsin ⁇ t and coming directly from the 'local oscillator OL.
• two configurable test signals TXI and TXQ are given to the two inputs BI and BQ of the mixer, given respectively by formulas (1) and (2).
• TXI DCI + sin ⁇ t (1)
• TXQ DCQ + r cos ( ⁇ t + 0) (2)
• DCI represents the continuous component of the TXI signal, and sin ⁇ t the temporal sinusoidal component of pulsation ⁇ .
• DCQ represents the continuous component of TXQ signal, while r cos ( ⁇ t + 0) represents the cosine component of this TXQ signal. r represents the amplitude of this cosine component. It should be noted in this regard that since the amplitude of the sinusoidal component of the signal TXI has been chosen equal to 1, r here in fact represents the ratio of the amplitudes of the two periodic components of the two test signals. Likewise, 0 represents the relative phase shift of the two periodic components of the two signals TXI and TXQ. If the mixer Q was perfect, the output signal SS would only comprise a line called useful line RU centered on the frequency FL-tf, where FL is the frequency of the local oscillator (corresponding to the pulsation
• the output spectrum of the signal SS comprises, in addition to the useful line RU, two parasitic lines (FIG. 2), namely the line RL of local oscillator centered on the frequency FL and an image line RM centered on the frequency FL-f.
• Adjusting the output spectrum of the DTF mixer consists in varying the different parameters of the two test signals so as to minimize the level or power P of the parasitic lines RM and RL.
• the prior art adjustment method consisted in varying the parameters of the TXI signal according to a given scanning step, keeping the parameters of the TXQ signal constant and then repeating this scanning on the Q channel while keeping the parameters of the TXI signal constant. . These two iterative scans were then repeated with smaller scanning steps until the values of the parameters having led to the obtaining of a minimum level for the line RM and the line RL were selected.
• the invention proposes a method radically different from this, which requires only a few measurement points.
• DCI, DCQ, r and 0 represent the current test values of the different parameters
• DCIO, DCQO, rO and 00 represent the reference values of these parameters for which the power of the line RL and the power of the IM line are zero.
• Kl and K2 are constants.
• the purpose of the adjustment therefore consists in determining by calculation these reference values. This determination is made in a BTR processing block (FIG. 1) comprising conventional means of spectrum analysis MS and processing means MT such as a microprocessor.
• the reference PBL1 designates the correlation paraboloid between the power of the line RL and the different values of the parameters DCI and DCQ.
• the section of the paraboloid PBL1 in the DCQf plane is a PBI parabola as illustrated in FIG. 4.
• a first variant of the invention for determining the reference value DCIO and the reference value DCQO will consist in using the fact that the derivative of a parabola is a straight line and will consist in finding the point POR where this derivative is zero . More precisely, one fixes for the other parameters DCQ, r and 0, predetermined values DCQf, rf, and 0f.
• test values are also chosen for the DCI parameter, namely the DCU, DCI2, DCI3 and DCI4 test values, and the corresponding test signals TXI and TXQ are successively applied.
• the measurement means MS of the processing block BTR determine then for each of the points PO1, P02, P03 and P04 of the parabola PBI the corresponding levels PI, P2, P3 and P4 of the local oscillator line RL. From there, for the triplet of measuring point PO1, P02 and P03, the value of the derivative P'2 at point P02 is determined by formula (5).
• the value P'3 of the derivative at point P03 is determined by formula (6).
• the two measurement points P02 and P03 having coordinates (P'2, DCI2) and (P'3, DCI3) respectively, allow to determine the two parameters ⁇ and ⁇ of the line D of equation:
• Obtaining the reference value DCIO was therefore carried out by a simple numerical calculation, carried out in software within the processing means MT of the processing block BTR and required only four separate measurements of the level of the corresponding line RL to four different DCI1-DCI4 test values for the DCI parameter.
• this variant of the invention required, for a given frequency FL of local oscillator, eight measurements of the level of the line RL to determine the reference values DCIO and DCQO of the parameters DCI and DCQ (four measurements corresponding to the four different DCI1-DCI4 test values and four measurements corresponding to the four different DCQ1-DCQ4 test values).
• DCIO reference value is calculated as follows:
• relation (3) can take the form of relation (10).
• An analogous calculation can be carried out to determine the reference values rO and 00 of the pair of parameters r and 0 using this time the level of the image line IM and the relation of the paraboloid type given by the formula (4) below. before.
• the reference values which have just been obtained have been calculated for a given value of the local oscillator frequency. This calculation can be performed for all the local oscillator frequencies corresponding to the different frequencies of the transmission channels subdividing the radio frequency transmission band of a mobile telephone (for example sixty channels extending in the frequency band 850 MHz- 950 MHz).
• the DTF mixer is preceded by an auxiliary circuit CX formed by two channels VX1 and VX2 respectively connecting the two input terminals BI and BQ from the mixer to a BX terminal receiving the useful signal, in this case the voice.
• the VX1 channel includes an amplifier
• the channel VX2 comprises time delay means MR, for example a delay line, followed by a variable gain amplifier AM2, followed by an adder AD2 also also receiving an auxiliary voltage from a second auxiliary voltage source ST2.
• the value of the auxiliary voltage ST1 corresponds to the parameter DCI, while the value of the auxiliary voltage ST2 corresponds to the parameter DCQ.
• the variable gain of the amplifier AM2 corresponds to the parameter r and the time delay induced by the delay means MR corresponds to the phase shift 0.
• the value of the time delay, the gain value of the amplifier AM2 and the values of the auxiliary voltages ST1 and ST2 can be adjusted, so that these values correspond to the reference values. 00, rO, DCIO and DCQO obtained when adjusting the mixer.
• the BTR processing block comprising a spectrum analyzer and a processor, generally present in any mobile phone, permanently receives the output signal from the DTF mixer.
• the mobile telephone is locked for predefined elementary durations (for example 12.5 ms) on a selected frequency channel.
• the invention therefore provides, for example at the start of the elementary locking duration, to switch the input of the auxiliary circuit CX to a generator GEN generating a periodic auxiliary signal, by example a sinusoidal signal.
• the processor included in the processing block BTR then varies the values of the auxiliary voltage sources, that of the gain of the amplifier AM2 and the value of the delay of the delay means MR, and determines by a digital calculation analogous to that which comes to be described, the different reference values taking into account the current frequency of the local oscillator and the actual operating conditions of the telephone.
• the processor switches the input of the auxiliary circuit CX to the input receiving the speech SU.

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Monitoring And Testing Of Transmission In General (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9531932

Family Applications (1)

Country Status (4)

Families Citing this family (6)

Family Cites Families (2)

• 1998
  • 1998-10-23 FR FR9813332A patent/FR2785111B1/fr not_active Expired - Fee Related
• 1999
  • 1999-10-20 US US09/420,962 patent/US6393258B1/en not_active Expired - Lifetime
  • 1999-10-22 EP EP99949091A patent/EP1125411A1/de not_active Withdrawn
  • 1999-10-22 WO PCT/FR1999/002570 patent/WO2000025494A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events