Method and device for generating radar signals for measuring the distance and relative speed between two objects

Abstract

Method for generating radar signals for measuring the distance and the relative speed between at least two objects, in particular in a road space, by means of a phase-locked loop comprising - a phase detector, - a filter, - a voltage-controlled oscillator and - a frequency divider, where - in one cycle, the frequency of the signal at the output of the frequency divider is increased and / or decreased in steps by changing a division factor N in order to produce a linearly increasing or almost linearly increasing or decreasing voltage at the output of the filter and - a first voltage with at least two voltage levels is added to the voltage at the output of the filter.

Description

[0001] The invention relates to a method and a device for generating radar signals for measuring the distance and the relative speed between two objects, in particular in a road space.

[0002] Motor vehicles are increasingly being equipped with radar systems to measure the distance of objects to the vehicle and their relative speed. The measured distances and relative speeds can be used in various driver assistance systems. These driver assistance systems can include, for example, automatic headlight range control, automatic selection of light distribution, automatic adjustment of vertical or horizontal cut-off lines, brake assist, and other functions.

[0003] European patent publication number EP 1 325 350 B1 discloses a method and device for determining the distance and relative speed of an object distant from a motor vehicle. The patent proposes an FMFSK (frequency modulated frequency shift keying) method. The device using this method has a voltage-controlled oscillator with which several signals to be transmitted are generated. Each signal has several sections with different frequencies that remain constant throughout the section. The sections are transmitted one after the other, with the frequency of the signal sections of a signal increasing from section to section. However, the sections of a signal are not transmitted directly one after the other. Rather, each section of one of the signals is followed by a section of another signal.The transition between the signal sections always occurs in the same order and is repeated in each bar. This creates nested signal sections. The frequency of the signal is always maintained during each signal section.

[0004] To achieve the best possible results with this method, only voltage-controlled oscillators with certain basic properties can be used, particularly regarding the slope, curvature, aging, and temperature drift of the voltage-controlled oscillator. Therefore, during the manufacture of a device as described in the patent, all voltage-controlled oscillators are measured before assembly, and only suitable controlled oscillators with the same properties are selected. Furthermore, cycles are regularly inserted into ongoing operation during which the voltage-controlled oscillators are calibrated, for example, to compensate for temperature drift. Calibration is performed using a phase-locked loop. During the calibration cycles, the devices cannot be used to generate radar signals for measuring distance and relative speed.This is not beneficial for driver assistance systems, where no current data from the road surface can be provided during this time. Furthermore, a relatively expensive 12- to 16-bit digital-to-analog converter (DAC) is required. The higher the accuracy requirements of the radar system and the poorer the voltage-controlled oscillator, the more bits the DAC requires.

[0005] In addition, sorting out unsuitable voltage-controlled oscillators is complex and costly.

[0006] Similar methods for generating radar signals are disclosed in US 6,018,275 A; in US 5,940,457 A and in DE 10 2004 030 841 A1.

[0007] This is where the present invention comes in.

[0008] The present invention is based on the problem of proposing a method for generating radar signals for measuring the distance and the relative speed between two objects, which can be carried out with a cost-effective device and at the same time makes a cycle for calibrating the controlled oscillators unnecessary.

[0009] This problem is solved by a method according to claim 1 and by a device according to claim 9.

[0010] According to the invention, a phase-locked loop is used to generate radar signals for measuring the distance and relative speed between two objects. This comprises a phase detector, a filter, a voltage-controlled oscillator, and a frequency divider. In each cycle of the radar signals to be generated by the method, the frequency of the signal present at the output of the frequency divider is gradually increased and / or decreased by changing a division factor of the frequency divider. This results in a linear or nearly linear increase or a linear or nearly linear decrease in the voltage at the output of the filter. In addition, a first voltage with at least two voltage levels is added to the output voltage of the filter.

[0011] A phase-locked loop is described, for example, in the technical documentation "Technical Brief SWRA029, Fractional / Integer-N PLL Basics" by Texas Instruments, Inc. A phase-locked loop is constructed such that the inputs of the phase detector receive the signal from a time base and, via the frequency divider, the feedback output signal of the voltage-controlled oscillator. An input of the phase-locked loop's filter or controller is connected to the output of the phase detector. The filter output is connected to the voltage-controlled oscillator.

[0012] Changing the frequency divider's division factor changes the output signal at the phase detector's output. From a control engineering perspective, the phase detector indicates a control error, which the filter attempts to compensate for in its function as a controller. Due to the filter's inertia, the invention produces a linearly rising or falling voltage at the filter's output.

[0013] According to the invention, the first voltage is then added to the filter's output signal. The filter's output signal is thereby increased or decreased in sections by the voltage levels of the first signal. The voltage-controlled oscillator generates an output signal accordingly. The output signal of the voltage-controlled oscillator is divided into sections, with the signal frequency increasing linearly in each section. Corresponding to the number of voltage levels of the first signal, sections follow one another in the output signal of the voltage-controlled oscillator, whose frequency increases abruptly compared to the previous section.

[0014] A new method for generating radar signals is to use a phase-locked loop to generate radar signals in order to use the radar signals to measure the distance and relative speed between two objects.

[0015] Another novel feature is that, in a method for generating radar signals, the change in the division factor is used to generate radar signals with a linearly increasing or decreasing frequency within a clock cycle. The method according to the invention utilizes the inertia of the phase-locked loop filter, which cannot keep pace with the stepwise change in the division factor of the frequency divider during a clock cycle. During a clock cycle, the phase-locked loop therefore does not reach a steady state, resulting in a linearly increasing or decreasing voltage at the filter output, which—if the first voltage is neglected—results in an output signal from the controlled oscillator with a linearly increasing frequency.

[0016] Another novel feature is the ability to use the first voltage to generate a gradual increase or decrease in the frequency of the voltage-controlled oscillator's output signal by voltage steps predetermined by the first signal. This results in gradual gradations in the frequency of the voltage-controlled oscillator's output signal. However, during such a step in the voltage-controlled oscillator's output signal, the frequency increases or decreases linearly, in contrast to the prior art.

[0017] The frequency divider's division factor in successive clock cycles can be alternately increased and decreased. This makes it possible to generate so-called "up chirps" and "down chirps," similar to the state of the art.

[0018] The division factor can be a natural number or a positive rational number. This means that in addition to a so-called integer-N PLL, a fractional PLL can also be used, in which a noise-shaping random pattern (MASH) of natural numbers is successively input to the integer-N PLL as division factors, allowing fractional numbers to be represented as well.

[0019] The first signal preferably has a period that is shorter than one cycle of the output signal or the radar signal to be generated.

[0020] A first stage of the first voltage can have a value of 0 V. This means that the output voltage of the filter is fed to the input of the voltage-controlled oscillator without increasing or decreasing. The frequency of the output signal of the voltage-controlled oscillator, i.e. the frequency of the radar signal, then corresponds to the voltage at the output of the filter. The first voltage can then be increased or decreased from stage to stage within a period of the first voltage. Accordingly, the input voltage of the voltage-controlled oscillator is increased or decreased from stage to stage compared to the output voltage of the filter. This results in a step-by-step increase or decrease in the frequency of the output signal of the voltage-controlled oscillator, i.e. the frequency of the radar signal.

[0021] In a simple case, the first voltage can be a square wave.

[0022] A device according to the invention comprises a frequency divider having an input at which the division factor can be adjusted. Furthermore, in a device according to the invention, an adder is arranged between the filter and the voltage-controlled oscillator. A first input of the adder is connected to a means for generating a first voltage. A second input of the adder is connected to the output of the filter. The output of the adder is connected to the input of the voltage-controlled oscillator.

[0023] The addition element may be comprised of a digital-to-analog converter with which it is possible to generate the first voltage and add it to the output voltage of the filter.

[0024] The phase detector, the filter, the voltage-controlled oscillator and the frequency divider can be arranged in an integrated circuit.

[0025] The invention is explained in more detail below with reference to the accompanying drawings. In the drawings: Fig. 1 is a block diagram of a device according to the invention, Fig. 2 a schematic representation of the input voltage of a voltage-controlled oscillator of the device according to Fig. 1, Fig. 3 a measured frequency response of the output signal of the voltage controlled oscillator of the device according to Fig. 1 and Fig. 4 a partial enlargement of the illustration according to Fig. 3.

[0026] The device according to the invention, to which in the Fig. 1, the block diagram is shown, has a voltage-controlled oscillator whose output signal V Tx(t) is the radar signal used to measure the distance and relative speed between two objects. The device can be used in a motor vehicle to determine the distance from the motor vehicle to other objects in the road space, such as preceding or oncoming vehicles, road signs, guardrails, or the like. It is also possible to use the device to determine the relative speed between the motor vehicle and the other objects.

[0027] The voltage-controlled oscillator is integrated into a phase-locked loop. In addition to the voltage-controlled oscillator, the phase-locked loop includes a frequency divider, a phase detector, a filter, and an adder.

[0028] The output signal V Tx(t) of the voltage-controlled oscillator is fed to the frequency divider. The frequency divider sets a signal at its output whose frequency is different from the frequency of the output signal v Tx (t) of the voltage-controlled oscillator. The division factor N by which the frequency of the output signal v Tx The amount by which the voltage-controlled oscillator's frequency can be increased or decreased (t) can be adjusted using the frequency divider. The frequency divider has an input for this purpose.

[0029] The output signal of the frequency divider is fed to the phase detector, for which the phase detector has an input. In addition to the input for the output signal of the frequency divider, the phase detector also has an input for a signal v F (t) of a time base. The signal v F(t) of the time base is a reference signal or, in control terms, a command value for the control loop formed by the phase-locked loop. In the phase detector, the signal v F (t) of the time base and the output signal of the frequency divider are compared. The result of the comparison is provided at the output of the phase detector, which is connected to the input of the filter. The filter forms the controller in the phase-locked loop. At the output of the filter, a control signal v generated by the filter can be applied. R (t) and routed to the outside. The information for tuning the voltage-controlled oscillator is contained in the voltage at the filter's output.

[0030] A special feature of the device according to the invention is that the output signal of the filter is deliberately disturbed. For this purpose, an adder is provided between the output of the filter and the input of the voltage-controlled oscillator, to which a first voltage v s (t) is added to the filter's output voltage. The sum of both voltages is fed to the voltage-controlled oscillator, which accordingly adjusts the frequency of its output signal v Tx (t). The sum of the two voltages can also be used as an alternative to the control signal v R (t) are fed out. Both can be used to estimate the slope (MHz / V) in order to either adjust the size of the frequency jumps by readjustment or to determine them.

[0031] The method according to the invention, which is carried out with the device according to the invention according to Fig. 1, makes use of the inertia of the filter to generate a linearly increasing or decreasing voltage at the filter output. In order to bring about the linear voltage increase or the linear voltage decrease at the filter output, the division factor of the frequency divider is increased or decreased step by step. This changes the frequency at the frequency divider output. The change in the frequency of the frequency divider output signal leads to a signal at the phase detector output which causes the linear voltage increase or linear voltage decrease at the filter output. The inertia of the filter means that the device according to the invention cannot correct the control deviation at the filter input within one clock cycle. The phase-locked loop therefore does not enter a steady state within one clock cycle.

[0032] The deliberate disturbance of the output signal of the filter, ie the addition of the first voltage v S (t) to the output voltage of the filter leads to a voltage at the input of the voltage controlled oscillator, which is qualitatively Fig. 2. In this case, the first voltage is a square wave with a period shorter than the radar signal clock. The square wave leads to a section-by-section, abrupt increase in the input voltage of the voltage-controlled oscillator. The steps in the input signal of the voltage-controlled oscillator cause sections of increased frequency in the output signal v Tx (t) of the voltage-controlled oscillator or in the radar signal v Tx (t).

[0033] This is in the Fig. 3 and Fig. 4 for the case of a linearly decreasing voltage v R (t) at the output of the filter.

[0034] The frequency jumps in the output signal v Tx (t) of the voltage-controlled oscillator are so small that, due to the inertia of the filter, they cannot be detected during one cycle of the output signal v Tx (t) or radar signal can be adjusted.

Claims

[1] Method for generating radar signals for measuring the distance and the relative speed between at least two objects, in particular in a road space, by means of a phase-locked loop comprising - a phase detector, - a filter, - a voltage-controlled oscillator and - a frequency divider, where - in one cycle, the frequency of the signal at the output of the frequency divider is increased and / or decreased in steps by changing a division factor N in order to produce a linearly increasing or almost linearly increasing or decreasing voltage at the output of the filter and - a first voltage with at least two voltage levels is added to the voltage at the output of the filter. [2] Method according to claim 1, characterized by that the division factor of the frequency divider is alternately increased and decreased in successive cycles. [3] Method according to claim 1, characterized by that the division factor is a natural number or a positive rational number. [4] Method according to one of claims 1 to 3, characterized by that the first voltage has a period that is shorter than the clock. [5] Method according to one of claims 1 to 4, characterized by that one stage of the first voltage has a value of 0 V. [6] Method according to one of claims 1 to 5, characterized by that the first voltage is increased from stage to stage during a period. [7] Method according to one of claims 1 to 5, characterized by that the first voltage in a period is reduced from stage to stage. [8] Method according to one of claims 1 to 7, characterized by that the first voltage is a square wave voltage. [9] Device for generating radar signals for measuring the distance and the relative speed between two objects, in particular in a road space, in particular for carrying out a method according to one of claims 1 to 8, comprising - a voltage-controlled oscillator characterized by , that the device further comprises - a phase detector, - a filter, - a frequency divider, wherein the phase detector, the filter, the voltage-controlled oscillator and the frequency divider are arranged in a phase-locked loop, that the frequency divider has an input at which the division factor can be adjusted and that between the filter and the voltage-controlled oscillator there is arranged an adder which has a first input connected to a means for generating a first voltage, which has a second input connected to the output of the filter, and whose output is connected to the input of the voltage-controlled oscillator. [10] Device according to claim 9, characterized by that the addition element is comprised of a digital-to-analog converter. [11] Device according to claim 9 or 10, characterized by that the phase detector, the filter, the voltage-controlled oscillator and the frequency divider are arranged in an integrated circuit.

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