Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
1999-10-20
2002-05-21
Hunter, Daniel (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S067150, C455S115200, C455S118000, C455S111000, C455S104000, C375S295000, C375S296000
Reexamination Certificate
active
06393258
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of electronics, and, more particularly, to a system and method for adjusting a radio-frequency emission spectrum.
BACKGROUND OF THE INVENTION
In a mobile telephone, the useful signal emitted, in this instance voice, is a low-frequency signal transposed into a high-frequency signal using an IQ mixer with the aid of a high-frequency signal originating from a local oscillator. The output spectrum of the signal provided by the mixer therefore contains a so-called useful line. This corresponds to the useful signal transposed to high frequency, and to the spurious lines. The spurious lines in this instance are the line of the local oscillator signal as well as the image line of the useful signal.
When a mobile telephone is locked for a predetermined duration, e.g., 12.5 ms, onto a transmission frequency channel, it is necessary for the spectrum of the signal emitted to occupy the least possible pass band to disturb as little as possible the other transmission frequency channels which may be allotted to other radio-frequency transmitters/receivers. Also, the local oscillator line and the image line can disturb the other channels. The adjusting of the mixer is therefore aimed at canceling, or at the very least at decreasing the levels of the spurious lines, i.e., the level of the image line and of the local oscillator line.
Adjustment includes tailoring the symmetry of the low-frequency input signals of the mixer to compensate for the internal asymmetries of this component which are responsible for increasing the image and local oscillator lines of the output spectrum. In this regard, two parameter test signals are delivered respectively to the input of the two paths I and Q of the mixer. Each test signal typically has a DC component and a periodic component. The periodic component is typically sinusoidal. The periodic components of the two test signals are mutually phase-shifted. The adjustment includes tailoring the value of the DC components for a fixed value of the frequency of the local oscillator signal. The adjustment also includes adjusting the ratio of the amplitudes of the two sine components and the value of the phase shift to minimize the levels of the spurious lines.
A conventional method for carrying out this tailoring includes performing a sweep on the input path I, and then on the path Q, for each possible local oscillator frequency associated with a transmission channel. The various values are measured for the parameters of the test signals, along with the levels obtained for the image and local oscillator lines. This operation is repeated while refining the sweep step size until the desired rejection is obtained. Parameter values are thus obtained making it possible to obtain very low levels for the image and local oscillator lines.
However, this method has the drawback of requiring a very considerable number of measurements, typically on the order of a few tens to a few hundreds for a local oscillator frequency value. Consequently, this provides a very long adjustment time. Moreover, the adjustment is currently performed with a nominal supply voltage. Furthermore, a check is made as to whether, at the end of the life of the battery of the telephone, the quality of the output spectrum of the mixer is still in accordance with the desired specifications.
However, during the operation of a telephone, the variations in the supply voltage and/or in the temperature in particular, may modify certain characteristics of the transistors forming certain elements of the mixer. This may consequently modify its behavior, and in particular, the internal asymmetries. Hence, this results in a misfit 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 to be performed in real time. Such a real-time adjustment, i.e., for a duration in which the telephone is locked onto a transmission channel, is totally incompatible with the duration of adjustment currently required.
Furthermore, the effectiveness of the current method is poor as it becomes closer to the solution. This is because the measurement noise, although very low, tends to trap the iterative search algorithm in a local minimum. This leads to obtaining reference values or optimal values for these parameters which are different from the theoretical reference values.
SUMMARY OF THE INVENTION
An object of the invention is to provide an adjustment for the output spectrum of an IQ mixer that requires a very low number of measurements to determine the parameters of the test signals applied to the IQ mixer.
Another object of the invention is provide an adjustment to the input signals applied to the IQ mixer which can be implemented in real time in a mobile telephone.
A further object of the invention is to increase the effectiveness of the above described adjustment.
The invention results, in particular, from the fact that it has been found that it is possible to correlate the power level of the image and local oscillator lines of the output spectrum with the various parameters of the test signals via two parabolic mathematical relations. On the basis of this, the determination of the reference or optimal values for the relevant parameters, and reference values corresponding to theoretically zero levels of these spurious lines can be performed by a numerical calculation on a reduced number of measurements. This is typically a few measurement points.
The invention is therefore distinguished from the prior art, in particular, by the fact that the determination of these reference values is performed by a numerical calculation, while in the conventional method this determination is performed solely by observing the measured levels of a very large number of points. This is done for selecting the values of the parameters that have led to a minimum level.
The invention thus makes it possible to decrease the duration of the adjustment in a ratio of greater than ten. This decreases the cost of products incorporating such a mixer given that the cost of the test represents a considerable percentage of the cost of these products. Furthermore, the duration of such an adjustment according to the invention makes it possible, if necessary, to implement such an adjustment in real time during the operation of a mobile telephone.
Stated otherwise, the invention therefore provides a process for adjusting the level of the spurious lines of the output frequency spectrum of a single-sideband frequency mixer. This process comprises the steps of:
delivering at the input of the two paths of the frequency mixer two mutually phase-shifted test signals each having a plurality of parameters;
measuring the level of each of the spurious lines for different test values of the various parameters of the two test signals; and
determining reference values for the various parameters making it possible to minimize the levels of the spurious lines.
According to a general characteristic of the invention, the reference values are determined by a numerical calculation performed on a predetermined number of different test values of the parameters and corresponding measured values of the levels. This is done with respect to two parabolic type relations linking the levels of the two spurious lines with the parameters to minimize the duration of adjustment by using a reduced number of test values.
According to one mode of implementation of the process, each test signal comprises a DC component and a periodic component, e.g., a sine component. The DC components of the two test signals form respectively first and second parameters. The ratio of the amplitudes and the relative phase-shift of the two periodic components of the two test signals form respectively third and fourth parameters. The spurious lines comprise an image line and a local oscillator line. The first and second parameters are linked to the level of the local oscillator line by a first parabolic relation, while the third a
Fournier Vincent
Gambina Maria Luisa
Jorgenson Lisa K.
STMicroelectronics S.A.
Zewdu Meless
LandOfFree
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