Process for measuring distance with adaptive amplification

A process for determining the distance between a distance sensor and an object, wherein an analog input signal is directed to a transmitter of the distance sensor. The transmitter emits a wave which is reflected by the object. A receiver of the distance sensor receives the reflected wave and thereupon emits an analog output signal whose level is dependent upon the distance and/or the type of object. The output signal is amplified by a subsequently added amplifier. The amplifier signal is directed to an analog/digital converter and is converted into a digital signal. The digital signal is directed to an evaluation circuit for the computation of a distance value. The signal amplification of the amplifier is controlled in an adaptively dependent manner on the level of the output signal and/or in a manner dependent on the signal value of an amplification signal made available by the evaluation circuit which is characteristic of an anticipated distance range.

The invention relates to a process or a device for determining the distance 
between a distance sensor and an object. Furthermore, the present 
invention relates to a process for producing user information that enables 
the driver of a motor vehicle to assess, in a manner adapted to the 
situation, the configuration of an obstacle. 
In many areas of technology, distances must be determined. In motor vehicle 
technology, for example, it is already known to use distance measuring 
systems to aid the driver while he is entering and leaving a parking 
space. These systems are based mostly on the ultrasound principle, wherein 
the sensor heads are integrated, depending on the layout, in the rear 
bumper or in both bumpers. Furthermore, distance measuring systems have 
already been proposed which make it possible for the driver to monitor, 
while driving, the distance from the vehicle in front. These distance 
measuring systems must be able to measure substantially greater distances 
than the previously addressed parking aids. 
One pump of the present invention is to indicate a distance determining 
process that has a high degree of measuring precision at close range and 
simultaneously encompasses a large measuring range. Furthermore, one 
purpose of the present invention is to create a device for determining the 
distance that has a high degree of measuring precision at close range, has 
a large measuring range and simultaneously can be manufactured in a 
cost-efficient manner. 
Due to the adaptive control of the signal amplification that is dependent 
on the level of the output signal and/or is dependent on the signal value 
of an amplification command signal that is provided by the evaluation 
circuit, the dynamic output voltage range of the amplifier is adapted in 
an optimum manner to the transfer characteristic of the subsequently added 
analog/digital converter. Thereby, the quantization error is minimized 
that occurs unquestionably as a result of the system-related limited 
resolution of the analog/digital converter during the conversion of the 
amplified analog signal into a number with a finite number of bits. This 
makes it possible, on one hand, to achieve a high degree of measuring 
precision in the case of small distances and, on the other hand, to also 
use the process for the measurement of great distances. 
This can be understood in the following manner. The reflected wave has an 
amplitude height which is dependent upon the distance of the object as 
well as on the type of object, for example, its spatial extent, 
reflectivity, etc. When small distances or large objects are measured, the 
reflected wave has, as a rule, very high amplitude values. The analog 
output signal emitted by the receiver then also shows a very high level 
value. If this level value were to be amplified by an amplifier with a 
constant amplification, i.e., an amplification independent of the level, 
this would necessitate an analog/digital converter which could still 
convert the amplified, high level value. Therefore, such an analog/digital 
converter must have a very wide dynamic range. However, since the 
quantization noise of an analog/digital converter with constant resolution 
(N-bit converter, N=constant) rises with increasing dynamic range, a 
lesser measuring precision should be taken into consideration in this 
case. Alternatively, it would be possible to use an analog/digital 
converter with a higher resolution (M-bit converter, M&gt;N), whereby it 
would be possible to increase the measuring precision while, however, the 
component costs will increase. By means of the adaptive amplification of 
the output signal found with the present invention, it is possible, in the 
case of a high amplitude value of the reflected wave, to effect a 
suitable, low amplification by means of the amplifier, whereby an 
analog/digital converter with a limited dynamic range and thus, in the 
case of a fixed resolution, increased signal sensitivity, can be used. The 
process of the invention thus makes possible a distance measurement with a 
high degree of sensitivity, as required in the case of distance measuring 
systems used in motor vehicles, particularly at close range. 
On the other hand, with the measurements of great distances, relatively 
small amplitudes of the reflected wave are to be expected. The adaptive 
amplification of the invention produces in this case a comparatively 
strong signal amplification and thereby prevents the amplified signal from 
dropping below the detection threshold of the analog/digital converter. 
Consequently, also great distances can be measured safely, i.e., a large 
measuring range is obtained. 
According to a preferred embodiment of the process of the invention, the 
input signal is a pulse signal and the distance determination takes place 
according to a pulse duration process. Such a process is particularly 
suited during the use of a radar sensor as a distance sensor. The use of a 
pulse duration process characterizes itself as an advantageous distance 
gauging process in that the signal value of the amplification command 
signal, upon the appearance of a pulse, respectively, rises in the input 
signal until the next pulse appears in the input signal. Thereby, it is 
possible to amplify waves, reflected by distant objects and arriving at a 
later time, with a higher amplification and thereby the measuring range 
can be increased to greater distances. 
When a pulse duration process is used, it is also advantageous when the 
time span between the appearance of two pulses is divided into a sequence 
of time windows and to each time window a predetermined signal value of 
the amplification command signal is assigned. While the measuring range 
can be influenced by predetermining the individual signal values with 
respect to the time windows, it is possible by predetermining the duration 
of the individual windows between two pulses to determine the measuring 
precision. Since in the case of greater distances a smaller measuring 
precision suffices than with smaller distances, the duration of a window 
occurring at a later time is preferably selected greater than the duration 
of a previously appearing time window between two pulses. 
The distance measuring process of the invention, due to its large measuring 
range, is particularly suited for use in a process for producing user 
information that aids a motor vehicle driver during a mode of responding 
in street traffic that is adapted to the situation. 
With such a process, the driving information data advantageously comprise 
at least steering angle data and driving speed data. 
According to an advantageous embodiment of this process, the object 
information data are subjected to a plausibility test via the second 
program routine, either prior to or during the further processing. For 
example, the plausibility test may consist in that object information data 
corresponding to suddenly appearing or also suddenly disappearing 
obstacles are rejected, since in reality such situations do not arise. By 
means of this step, driving safety can be further increased during 
practical operation. 
According to an additional advantageous modification, the second program 
routine comprises an evaluation routine that evaluates by means of the 
object data and the driving data the likelihood of danger posed by a 
detected obstacle, wherein a warning signal is emitted when the determined 
danger likelihood value exceeds a predetermined reference value. In this 
way, previously defined, particularly grave situations of danger can be 
pointed out to the user by the emission of the warning signal. 
By the provision of an amplifier with an adaptive signal amplification, the 
use of an analog/digital converter whose acquisition is cost-efficient is 
made possible because a high-resolution analog/digital converter as 
already described is not required. 
When the amplifier is integrated in the sensor, this allows the preparation 
of a low-resistance output signal, whereby in an advantageous manner a 
greater insensitivity of the device with respect to interferences is 
achieved during the transfer along longer conduction paths. 
A particularly simple embodiment of the amplifier with adaptive signal 
amplification is characterized in that the amplifier is formed from a 
logarithmic amplifier on the input side and a subsequently added amplifier 
phase with constant amplification. 
In an alternative manner, a level detector may be arranged before the 
amplifier that detects the level of the output signal and prepares a level 
signal that is then directed to a control input for the signal 
amplification of the amplifier.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
According to FIG. 1, a system for the perception of the environment 
consists of a multitude of radar sensors (1), preferably integrated in the 
bumper, which are in two way line connection with an evaluation circuit 
(2). The evaluation circuit (2) is connected via a line connection (3) 
with a bus system (4) of the vehicle, and a data output line (5) of the 
evaluation circuit (2) transfers audiovisual information data to the 
output unit (6) which, in a manner not shown, includes at least one 
display and one loudspeaker. 
FIG. 2 shows a block diagram of the circuit assembly of the evaluation 
circuit (2) with respect to an individual radar distance sensor (1). 
There, the broken line (7) gathers the circuit elements forming the 
evaluation circuit (2). 
The evaluation circuit (2) has a pulse generator (9) controlled by a 
microcontroller (8) which produces sinusoidal current pulse signals at 
regular intervals and directs these to a radar transmitter (10) of the 
radar distance sensor (1). Simultaneously, a counter, not shown in FIG. 2, 
is tripped. The radar transmitter (10) emits upon each incoming current 
pulse an electromagnetic wave packet (11) that spreads out in a defined 
direction away from the motor vehicle. The frequency of the wave packet 
lies in the micro- or millimeter wave range. If the wave packet (11) 
impacts, as shown in FIG. 2, with an object (12), it is reflected more or 
less strongly, depending on the size and material of the object (12). The 
reflected wave packet is identified in FIG. 2 with the reference symbol 
(13) and is picked up by a receiver (14) of the radar distance sensor (1). 
At that time, the total duration of the wave packets (11 and 13) is 
proportional to the distance between the radar distance sensor (1) and 
object (12). 
The receiver (14) converts the wave packet (13) into an output signal (15) 
which essentially has a sinusoidal shape. The amplitude of the output 
signal depends on the amplitude of the incoming wave packet (13) and thus 
depends in an equally sensitive manner on the distance, the size and the 
reflectivity of the object (12). The output signal (15) is directed to an 
amplifier (16) that has an input (17) that can adjust the amplification of 
the amplifier (16). The input (17) is connected via a control line (18) 
with the microcontroller (8) and is charged with an amplification command 
signal emitted by same and explained in greater detail in the following 
text. 
The amplified signal (19) is directed to an N-bit-analog/digital converter 
and from same is continuously converted into a binary number. The 
quantization error, which inevitably arises at this time, is smaller the 
greater the solution of the resolution (N) of the converter is, and the 
smaller the maximum input voltage of the converter is during the 
sinusoidal full-scale range, i.e., the dynamic range of the converter. The 
digital signal (21) produced by the analog/digital converter (20) is 
directed to the microcontroller (8). 
With the arrival of the digital signal (21) at the microcontroller (8), the 
counter, not shown, is stopped and the value is directed to a 
microprocessor (22). From the value, the microprocessor (22) computes the 
distance between the radar distance sensor (1) and the object (12) and 
returns same to the microcontroller (8). The output of the distance value 
to the output unit (6) then takes place via an interface (23) of the 
microcontroller. 
The amplification control through the amplification command signal takes 
place in the following manner: Directly after the transmission of an 
outgoing wave packet (11), at first a very slight amplification is set. 
If, shortly thereafter, an incoming wave packet (13) is registered, then 
the reflected object must be in the near field of the radar distance 
sensor (1). Due to the slight amplification, the high signal amplitude 
expected in this case is compensated for and thus it is possible to use a 
cost-efficient analog/digital converter with a limited dynamic range with 
a continuous lapse of time, the amplification of the amplifier (16) is 
then increased, so that even for great distances a signal amplitude is 
obtained that does not get lost in the quantization noise. This increases 
the distance measuring range of the system without the need for a 
high-resolution M-bit-analog/digital converter with M&gt;N. 
The amplification command signal may be selected in such a way that, 
between two pulses, a constantly increasing amplification is brought about 
within the amplifier (16). On the other hand, it is also possible to 
divide the time interval between two pulses into a sequence of time 
windows and to assign to each of these time windows a certain 
amplification value. The increase in the amplification then takes place in 
discrete steps during the transition from one time window to the next. 
According to the representation in FIG. 1, additional radar distance 
sensors may be connected to the microcontroller (8) and may be controlled 
by same in a similar manner. 
FIG. 3 shows an alternative possibility for the adaptive amplification 
adjustment according to the present invention, wherein the broken line (7) 
represents the system boundary of the evaluation circuit (2). 
The circuit according to FIG. 3 distinguishes itself from the structure 
shown in FIG. 2 in that a level detector (24) is added to the output of 
the radar receiver (14). The level detector (24) determines the amplitude 
of the output signal (15) and is connected via a line (25) in negative 
feedback with the amplification control input (17') of the amplifier 
(16'). The negative feedback control takes place in such a way that the 
greater the signal level determined by the level detector (24), the 
smaller the amplification is set. 
A deviation from the arrangement shown in FIG. 3 consists of the level 
value determined by the level detector (24) being made available to the 
microprocessor (8), whereupon same adjusts the amplification of the 
amplifier (16) in a manner similar to the one in FIG. 2 via the output of 
a suitable amplification command signal. 
A particularly simple, adaptive amplification control results when the 
amplifier consists of an amplification phase with a constant amplification 
and of a logarithmic amplifier connected before the amplifier. 
The examples shown in FIGS. 2 and 3 have in common that the input of the 
analog/digital converter is controlled in the best possible manner, 
independently of the output signal (15) of the sensor. For this purpose, 
the analog/digital converter (20) may also be integrated in the 
microcontroller (8). 
The circuit arrangement shown in FIG. 3 may be used even when the distance 
determination is not based on an operating time process. 
With the aid of FIG. 4, while referring to the preceding FIGS. 1 and 3, a 
process for the generation of user information is explained that allows a 
motor vehicle driver to assess the obstacle structure in a manner adapted 
to the situation. FIG. 4 shows the front or what could also be the rear 
bumper (26) of a motor vehicle, not shown in greater detail, into which 
two distance sensors are integrated. The distance sensors may be any type 
of sensor, but the example shown here is based on distance sensors (1) 
that operate according to the radar principle. The distance sensors (1), 
respectively, scan an environment that extends spatially horizontally 
(x-direction) and vertically (y-direction), and in this way, pick up an 
object (12'). The respective distance values are determined according to 
the preceding description during each scan and thus are available to the 
evaluation circuit (2). Simultaneously, via the bus system (4), data which 
are relevant to the driving situation, such as the current steering angle 
and the current vehicle speed, are required by the microcontroller (8). 
The continuously determined distance values, as well as the driving 
information data, are made available to the microprocessor (22) and are 
processed by same in the following manner. 
According to a first program routine, the microprocessor (22) continuously 
determines from the measured distance values the positions of the 
object(s) (12') detected and in the case of spatially extending objects, 
also data regarding the outer form of the object(s). By using a multitude 
of distance sensors (1) behind, in front of and possibly also lateral with 
respect to the motor vehicle, an obstacle scenario that mimics reality can 
be computed and constantly updated in this way. 
The first program routine for determining the obstacle scenario comprises 
algorithms, such as a digital filtering, an averaging of several data 
sets, a correlation, Fourier analysis, etc. 
The evaluation of the actual obstacle scenario with respect to the actual 
driving situation takes place in an additional step while taking into 
consideration the equally constantly updated driving data. Such an 
evaluation is necessary because a certain obstacle scenario, depending on 
the actual driving situation, may have an entirely different likelihood of 
danger for the driver. For this reason, in this second phase, for example, 
a predetermined movement trajectory of the motor vehicle is computed from 
the steering angle data and this is compared with the previously computed 
obstacle scenario while taking into consideration the speed data. For 
example, in this way, it can be determined whether the vehicle, when the 
speed is kept constant and the steering angle remains unchanged, will or 
will not scrape an obstacle during parking. This information is given to 
the driver as user information via the output unit (6) in the form of 
visual information or in the form of audio information. 
Furthermore, the user information computed in the second phase may also be 
used for the constant monitoring of the ride with respect to predefined 
danger situations. In this case, the user information is passed on to the 
driver only when an actually dangerous situation occurs. This can be 
achieved because the microprocessor (22) constantly computes a danger 
likelihood value within the framework of the second computation routine 
and compares same with a predetermined reference value. If the danger 
likelihood value exceeds the predetermined reference value, the driver is 
informed of this fact by means of an audible or optical warning signal. 
For example, the distance from the vehicle in front is constantly 
determined by means of the distance sensors (1) during normal driving. The 
speed data are then numerically divided by the measured distance data or 
connected through another suitable correlation. The value obtained at that 
time is the danger likelihood value and is compared with a previously 
entered reference value that represents a critical threshold for a vehicle 
following too closely. When a vehicle follows too closely or drives too 
fast, the warning occurs. 
In addition to the already addressed areas of application as a parking aid 
and a distance monitoring system, the process of the invention can also be 
used, due to its described advantages, for the purpose of a warning of an 
obstacle that was overlooked by the driver ("Blind Spot Detection") for 
the early recognition of an accident ("Pre-crash Detection") and as an aid 
during driving in heavy traffic ("Stop and Go Distance Measurement").