The present invention relates to a method for amplifying an echo signal suitable for detection of a vehicle's surroundings and a device for carrying out the method. The present invention also relates to a vehicle assistance system having a device according to the present invention for amplifying an echo signal suitable for detection of a vehicle's surroundings.
A method for amplifying an echo signal suitable for detection of a vehicle's surroundings is discussed in publication DE 10 2008 054 789 A1, in which a gain factor is set as a function of a transit time of the echo signal. A variable amplifier is provided for this purpose, the gain curve optionally also having a sudden course in multiple steps. A complex operational amplifier circuit in which resistances are activated and deactivated for a sudden change in gain is shown as an exemplary embodiment. This also describes how the curve of the sudden change in gain must additionally be calibrated by a central signal processor.
The same publication describes how in systems, which sense the surroundings and carry out pulse-wise measurements, the evaluation complexity may be reduced with the aid of a transit time-dependent gain V(τ) since the signal strength becomes lower with an increase in echo transit time. This describes a continuous change in the input gain which may take place since the received signal is much less falsified by a continuous change in comparison with a sudden change.
In systems of an optimal configuration, it should be possible to vary the gain V(τ) in the range of
where Vmax>100 from the standpoint of the system.
a and 1b show two possible curves of a desired transit time-dependent signal gain V(τ) as examples.
It is also believed to be understood from the related art how a transit time dependent gain may be implemented with little technical complexity by suitable wiring of an A/D converter, which may be in a recursive loop containing the signal reception, a certain part of the signal evaluation and optionally a suitable arrangement of generating a control signal for transit time-dependent gain regulation of an A/D converter in particular.
The recursive loop is not necessary for implementation of the transit time-dependent gain. If it is used, however, the transit time-dependent gain may be adapted to the prevailing signal situation, whereby the required dynamic range of the A/D converter may be reduced.
However, the technical implementation of amplifiers with a continuously adjustable gain is very difficult in particular because these amplifiers should also have a suitable dynamic range for the gain of incoming signals in addition to the adjustable gain range.
However, the implementation of N amplifiers having a fixed gain is implementable with very little effort. A very high gain
may be implemented by a series circuit with such amplifiers and the signal is present partially amplified at the transitions between the amplifiers in each case:
An equivalent situation applies for A/D converters. The range in which the reference voltage of A/D converters may be varied without any negative feedback effects on the quality of the A/D conversion is typically only in the range of 1 to 4.
There are therefore neither inexpensive A/D converters nor inexpensive variably adjustable amplifiers with which the required variable gain range
is implementable at approximately 50 kHz.
A method and a device according to the accompanying independent claims are made available.
With the method according to the present invention for amplifying an echo signal, an analog echo signal suitable for detection of a vehicle's surroundings is amplified with a gain which depends on the transit time of the echo signal. The analog echo signal is amplified with the aid of an amplifier having a plurality of outputs, each having a different, in particular fixed, gain and a downstream A/D converter having a time-variable reference voltage. The system is switched between different outputs of the amplifier at predefined switching points in time, and the reference voltage of the A/D converter is varied over time between the switching points in time, in such a way that the echo signal having a transit time-dependent total gain, which has a predefined characteristic, is present at the output of the A/D converter.
The device according to the present invention for a transit time-dependent gain of at least one echo signal, suitable for detection of a vehicle's surroundings, includes an amplifier having a plurality of outputs, each having a different gain, in particular a fixed gain, a downstream A/D converter having a time-variable reference voltage and a control device configured to switch between different outputs of the amplifier at predefined switching points in time and to generate a time-dependent total gain of the echo signal present at the output of the A/D converter and having a predefined characteristic with the aid of a suitable variation in the reference voltage of the A/D converter carried out between the switching points in time.
The further descriptions herein show refinements of the present invention.
Through a suitable variation of the reference voltage of the A/D converter between the switching points in time, a total gain of the echo signal, which is dependent on the transit time and has a desired characteristic, is generated from the partial gain of the echo signal generated by the amplifier between the switching points in time in a simple and economical manner.
Through suitable variation of the reference voltage of the A/D converter, the total dynamic range of the analog echo signal is easily imaged on a smaller effective total dynamic range, which results in a reduction in the computation effort required for evaluation of the echo signal.
The method according to the present invention also permits the use of an inexpensive A/D converter, whose reference voltage must be varied only in a small range.
In a particularly advantageous exemplary embodiment of the present invention, the analog echo signal is amplified with the aid of a series-connected chain of amplifiers of a fixed gain in particular and of the downstream A/D converter with the time-variable reference voltage.
The implementation of an amplifier by N series-connected amplifiers having a fixed gain is implementable at a very low cost and with low complexity in comparison with the implementation of an amplifier having a continuously adjustable gain. A very high gain
is implementable by the series connection of amplifiers. A partially amplified signal having a partial gain of
is present at the transitions between the amplifiers connected in series.
According to the present invention, the characteristic of the total gain is predefined in particular in pieces between the switching points in time.
Furthermore, according to the present invention, a method having a low level of complexity is made available for detection of a vehicle's surroundings with the aid of at least one echo signal in which at least one analog echo signal is amplified with the aid of a method according to the present invention, and at least the amplified echo signal for detection of a vehicle's surroundings is evaluated.
In addition, an inexpensive vehicle assistance system for detection of a vehicle's surroundings having a device according to the present invention for amplifying at least one echo signal suitable for detection of a vehicle's surroundings is made available according to the present invention, including an evaluation unit for detection of a vehicle's surroundings by at least one nonamplified echo signal and/or an echo signal amplified with the aid of the device according to the present invention.
Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings.
a shows one possible characteristic of a transit time-dependent signal gain according to the related art.
b show another possible characteristic of a transit time-dependent signal gain according to the related art.
The analog input signal (echo signal) ra in, which is dependent on transit time τ of the echo, having the usual center frequency of approximately 48 kHz in particular, has a basic gain V0 with the aid of basic amplifier 20. A downstream amplifier 30 includes N series-connected, cascaded amplifiers 40, 50 having a fixed gain Vfixed j, which results in a fixed total input signal gain
A fixed gain Vfixed
By varying the reference voltage of A/D converter URef AD(τ)|τ
For the total system, the variation in reference voltage URef AD(τ)|τ
In particular an inexpensive device 10 having an architecture with which the function of a desired, continuously adjustable gain is easily implementable in the required dynamic range
is provided according to the present invention.
With the aid of device 10 according to the present invention for gain and subsequent analog/digital conversion of signals ra in, a transit time-dependent gain V(τ) is implemented with the aid of a series-connected chain of amplifiers 40, 50 having a fixed gain Vfixed j at which there is a switch between different effective fixed partial gains Vfixed
In addition to the written disclosure above, reference is herewith made explicitly to the illustrations in
Number | Date | Country | Kind |
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10 2011 082 479.0 | Sep 2011 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2012/063945 | 7/17/2012 | WO | 00 | 10/14/2014 |