DE102014219925B4 - UWB radar microcontroller interface - Google Patents

Abstract

Ultra-wideband radar (1) for distance measurement, comprising the following features: - a transmitter unit (2) for emitting (31) an electromagnetic pulse signal (20) at a first time (to), - a receiver unit (3) for receiving (33) an echo signal (30) at a second time (t) or at at least one further time (t, ... tn), - a plurality of n current sources (4), - a plurality of n capacitors (5) having the plurality of n current sources (4) is electrically connected, and- an analog-to-digital converter (6) which is electrically connected to the plurality of n capacitors (5), wherein each power source (4) is associated with a respective capacitor (5) in that the n current sources (4) are each configured to start a charging of the respective associated capacitor (5) at the first instant (t) and to receive (33) a plurality of echo signals (30) at the second or at least one further instant (t, ... t) to be deactivated one after the other, and- the analogue digi tal converter (6) is configured, for each of the received echo signals (30) a respective voltage signal of the respective capacitor (5) at the second time (t) or the respective further time (t, ... t) in a first or a to convert another digital signal, wherein the voltage signal is proportional to the time duration (Δt) between the first time (t) and the second (t) or the at least one further time (t, ... t).

Description

The invention relates to an ultra-wideband radar for distance measurement and a method for distance measurement with an ultra-wideband radar.

Pulse radars in general and ultra wideband radars (UWB) in particular use very short signal pulses to determine the distance or distance of an object or object from the radar. For this purpose, an electromagnetic pulse is emitted by means of a transmitting antenna, wherein the typical duration of a pulse is in the range of a few picoseconds up to the microsecond range. The emitted pulse is reflected back by an object in the direction of the radar (echo) and received by the receiving antenna of the radar and recorded. From the duration of the pulse between the transmission of the pulse and the reception of the echo signal, the distance of the object to the radar can then be determined. The smaller the half width of the pulse, the more accurate the distance can be measured and the higher the achievable distance or range resolution. The running time depends on the distance of the object to the radar device and, depending on the application, ranges from a few picoseconds to a few hundred nanoseconds.

A simple approach to measuring the runtime is to start a counter with a sufficiently high clock rate when transmitting the pulse and stop it again when the echo is received. For a resolution of 100 ps, a clock rate or count frequency of 10 GHz is required.

A standard microcontroller that has clock cycles in the higher nanosecond range (typically several hundred nanoseconds), so is not able to directly measure maturities in the sub-nanosecond range. In addition, radar systems are widely used in environments where more than one target signal and interference is expected. Accordingly, a transmission pulse always also includes a plurality of echo signals, each of which includes destination information and disturbances. This information can not be processed with a simple timer.

From the state of the art, either high-performance analog-to-digital converters (ADC) with several gigasamples / second or high-precision high-frequency circuits for clock generation for digital meters are known for the conversion of UWB radar signals into the digital domain. The conversion of the signal by means of high-speed ADC has the advantage that the target acquisition can be done by software. However, the disadvantages are the extremely high costs for high-speed ADCs. In addition, even very good ADCs are not suitable to work in the lower picosecond range.

Another known approach is to start a first, slow counter with the transmit pulse and a second, faster counter with the echo pulse. It is then measured with a third counter the time that elapses until the fast counter has overtaken the slow counter. Depending on the ratio of the slow to the fast counter, the interval between sending the transmit pulse and receiving the echo can be stretched by several orders of magnitude. A disadvantage of this method is the high space requirement for this integrated circuit, especially when multiple destinations must be detected. Also, such solutions have a high power consumption.

Another approach to time measurement in a pulsed radar range sensor system is disclosed in US Pat DE 198 58 748 A1 demonstrated. Here, the time difference between a transmitted and a received signal is determined by means of a time-amplitude converter.

The operation of a time-amplitude converter component is, for example, in DE 10 2007 026 684 A1 explained. In the described time-amplitude converter, a capacitor is charged via a resistor network along a delay chain to obtain an analog voltage signal that is proportional to the time difference between two events.

In DE 36 14 850 A1 is presented another circuit for measuring the distance of an object. Similar to in DE 10 2007 026 684 A1 Again, a capacitor and its charging behavior is used to make a time measurement between a transmission signal and an associated echo.

Other known impulse radars and ultra-wideband radars and methods for operating the radars, in particular methods for measuring propagation time, are described, for example, in the documents US Pat. No. 7,202,812 B2 and or US 6,147,638 described.

There is a need for an improved ultra-wideband radar and a method for measuring the distance of multiple targets, the ultra-wideband radar having a high time resolution and at the same time low manufacturing and operating costs, in particular low power consumption.

The object of the present invention is to provide an improved ultra-wideband radar and a method for distance measurement, which overcomes the disadvantages known from the prior art. In particular, it is an object of the present invention to provide an ultra-wideband radar and a method for measuring the distance of several objects, the ultra-wideband radar and the method having both a high time resolution and low manufacturing and operating costs.

The above object is achieved by an ultra-wideband radar according to claim 1 and a method according to claim 14. Objects according to the dependent subclaims describe preferred embodiments of the invention.

A first aspect of the invention relates to an ultra-wideband radar for distance measurement according to claim 1.

A second aspect of the invention relates to a method for distance measurement with an ultra-wideband radar according to claim 12.

The invention is based on the knowledge of digitizing short time intervals via the detour of an analog variable. According to the invention, the time information is temporarily stored in a voltage signal and then converted into a digital signal with an analog-digital converter, in particular with a voltage-digital converter.

wobei
U die Spannung am Kondensator, I der Ladestrom, C die Kapazität des Kondensators und t die Zeit ist. Zeitgleich mit dem Empfangen eines Echosignales an einem zweiten, vom ersten Zeitpunkt verschiedenen Zeitpunkt wird die Stromquelle wieder deaktiviert, wobei die Spannung im Kondensator verbleibt und der Wert der Spannung proportional zur Zeitdauer zwischen dem ersten Zeitpunkt und dem zweiten Zeitpunkt ist. Anschließend wird das Spannungssignal mit Hilfe eines Analog-Digital-Wandlers digitalisiert.For this purpose, a plurality of current sources and a plurality of capacitors are provided according to the invention, which are electrically connected to each other. Simultaneously with the transmission of the pulse signal, namely at a first time, the current source is activated, so that the capacitor is charged. Charging causes the voltage on the capacitor to increase linearly according to the following relationship: $$\text{U}=\text{t}*\text{I}/\text{C}.$$

in which
U is the voltage at the capacitor, I is the charging current, C is the capacitance of the capacitor and t is the time. Simultaneously with receiving an echo signal at a second time other than the first time, the current source is deactivated again, leaving the voltage in the capacitor and the value of the voltage proportional to the time period between the first time and the second time. Subsequently, the voltage signal is digitized by means of an analog-to-digital converter.

Of particular advantage in the invention is the decoupling of the analog-to-digital converter of time-critical signals. The time information remains stored as a voltage in the capacitor until it is discharged again or read out. Also, the total power consumption of the radar according to the invention is rather low compared to known systems.

In the following, preferred embodiments of the ultra-wideband radar according to the invention and of the method according to the invention will be described.

The embodiment according to the invention provides that the ultra-wideband radar comprises a plurality of n current sources and n capacitors, each capacitor being associated with each current source. The value n can be any natural number 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8th . 9 . 10 etc. accept. With the transmission of the pulse signal, all n current sources are activated and the n capacitors begin to charge. With the reception of a further echo signal, one current source is switched off after the other, so that the different transit times of the different echo signals are stored by means of a voltage / a voltage signal at the different capacitors. In the present application, the term current source is also understood to mean a current sink, the charging current then having a negative sign. In principle, both alternatives, ie a positive or a negative charging current, are encompassed by the invention.

In an expedient embodiment, it is therefore provided that the n current sources are configured to charge the n capacitors from the first instant and with the emission of the electromagnetic pulse signal, and to be deactivated in succession upon receiving a plurality of echo signals at at least one further time, wherein the analogue Digital converter is configured to convert, for each of the received echo signals, another voltage signal of the corresponding capacitor in a further digital signal which is proportional to the time duration between the first time and the at least one further time. In this embodiment, for example, a switch arrangement, in particular a sample-and-hold circuit may be provided. Alternatively, however, it is also possible to provide a multiplexer or a plurality of analog-to-digital converters (ADC).

According to a currently particularly preferred embodiment, the current sources are controllable, wherein a charging current for the respective capacitor between 1 uA and 1 mA is adjustable. This embodiment serves to increase the measuring range. In particular, when more close targets are to be resolved more accurately, the charging current is set higher, so that the capacitors are charged faster. If, however, a higher range for the radar is desired, or is the signal propagation time is slowed down due to the irradiated medium, so the charging current is reduced, so that the charging times of the capacitors lengthen. The value range of the charging currents is in the range of about 1 μA to 10 mA for radar measurements in air.

A preferred embodiment provides that the capacitors are designed to be controllable, wherein a respective capacitance is variably adjustable between 0.1pF and 10nF. This embodiment again serves to increase the measuring range. The capacitors can be designed both as internal and as external components, wherein the use of controllable, external capacitors allows an additional enlargement of the measuring range.

In an advantageous embodiment, a first counter is provided for counting a plurality of echo signals, which is configured to associate each received echo signal with one of the n current sources and the n capacitors. In this embodiment, the first counter is connected to the n current sources and is set to zero when transmitting the pulse signal.

A preferred development provides at least one comparator which compares each echo signal with a predetermined threshold value and generates a corresponding output signal and forwards it to the first counter. In this development, the echo signal (s) is / are digitized via a comparator and then forwarded to an input of the first counter. Each echo signal that is above the predetermined threshold value of the comparator produces a rising or falling edge that continues to clock the first counter. Preferably, the threshold is designed to be adjustable and thus serves as an adjustable switching threshold for the comparator. Here, the switching threshold can be selected and set so that echo detection is performed with maximum sensitivity and minimum error rate, drifts, offsets and temperature effects are corrected in the echo signals. Also, the switching threshold can be controlled so that the so-called distance fading is compensated. In this case, the switching threshold for close targets with a high signal swing is set high and then reduced as the propagation time of the echo signals increases, so that even distant targets with weak echo signals are recognized well. Likewise, the switching threshold can be set at different levels for several consecutive measurements, e.g. to be able to make a statement about the envelope / amplitude of the echoes, or to generate a grayscale image.

In one embodiment, an overflow device is provided that is configured to output an overflow signal when more than n echo signals are received. This embodiment takes into account the case that more (> n) echo signals are received from the radar than capacitors are provided so that at least one target is not detected. In this case, an overflow signal is generated which can and should initiate further measures in order to enlarge and / or shift the measuring range accordingly.

A preferred embodiment provides a delay device which is configured to provide a variable, time delay after the emission of the electromagnetic pulse signal and before the charging of the capacitor, so that the capacitor is charged only after the time delay, at a later time, and the measuring range for the distance measurement shifts. In this embodiment, in particular, the connection between the comparator and the first counter is designed switchable by means of a switch. Also, in this case another, second counter can be provided and connected. If the second counter is fed by a reference clock source, a variable delay between the transmission of the pulse signal and the counting of the first echo signals can thus be set. If the second counter is fed by the comparator output, a variable number of first objects can be hidden. Both modes of operation are advantageous to increase the coverage of the radar. Are z. B. more targets than capacitors present in a first measurement, this number of targets can be ignored in a second measurement by the input of the first counter is then connected to the comparator output. In the same way, a so-called "sliding window" method can be used by increasing the delay in number of reference clocks by a certain factor after a first measurement in each further measurement. In this mode, individual targets may appear in multiple measurements as the different time windows overlap.

A preferred embodiment provides that the delay device is configured to provide a variable clock delay.

A preferred embodiment additionally includes a reference clock configured to set the variable time delay or the variable clock delay.

A preferred development of the ultra-wideband radar is configured to emit the electromagnetic pulse signals having a frequency of 10 kHz to several 10 GHz, preferably between 10 MHz to 200 GHz and even more preferably between 1 GHz to 100 GHz.

In an expedient embodiment, it is provided that the ultra-wideband radar is configured to integrate a plurality of voltage signals of the same capacitor in the distance measurement of a same object with a plurality of successive electromagnetic pulse signals. As described above, the first counter for a distance measurement is (normally) reset with the transmission of a pulse signal and the multiple current sources activated simultaneously. After a measurement has been completed and the capacitors have been read, they are discharged again and the radar is ready for the next measurement with the next pulse. For this purpose, a reset input of the first counter is triggered with the transmission of each transmission pulse. In the present embodiment, however, a further reset logic is provided before the reset input of the target counter. This reset logic allows the first counter to be reset without discharging the capacitors. This makes it possible to integrate several transmission pulses. Since the first counter is always reset, each incoming echo signal is always assigned to the same capacitor. The voltage applied to a capacitor at the end is therefore an average over several measurements with several transmitted pulse signals. An additionally present delay counter, which is clocked by a reference source, can preferably periodically control the reset logic so that an adjustable number of measurements can be automatically integrated before the voltages are read out.

• 1: eine schematische Darstellung einer möglichen Ausgestaltungsform eines Ultrabreitbandradars zur Abstandsmessung eines Objektes,
• 2: eine schematische Darstellung der Funktionsweise eines Ultrabreitbandradars, und
• 3: ein Ablaufdiagram für eine mögliche Ausgestaltung eines Verfahrens zur Abstandsmessung eines Objektes.

Further features and advantages of the invention will become apparent from the following descriptions of exemplary embodiments, reference being made to the following figures. In detail show:

• 1 : a schematic representation of a possible embodiment of an ultra-wideband radar for measuring the distance of an object,
• 2 : A schematic representation of the operation of an ultra-wideband radar, and
• 3 : a flow chart for a possible embodiment of a method for measuring the distance of an object.

1 shows a schematic representation of a preferred embodiment of an ultra-wideband radar 1 for distance measurement of an object, with a transmitter unit 2 , in particular a transmitter antenna, for emitting an electromagnetic pulse signal and a receiver unit 3 , in particular a receiver antenna, for receiving an echo signal.

In addition, the illustrated ultra-wideband radar includes 1 at least one power source 4 and a capacitor 5 , where the power source 4 and the capacitor 5 are electrically connected. With the present ultra-wideband radar 1 For example, the time intervals / duration between the emission of a pulse signal and the receipt of an echo signal are interim in a voltage signal at the capacitor 5 (between) and then with an analog-to-digital converter 6 , in particular with a voltage-to-digital converter, converted into a digital signal. This is the source of power 4 simultaneously with the transmission of the pulse signal, namely at a first time, activated, so that the capacitor 5 is charged. Charging causes the voltage on the capacitor 5 increases linearly. Receiving an echo signal at a second time different from the first time becomes the power source 4 deactivated again and it remains the charged voltage in the capacitor 5 , wherein the voltage is proportional to the time duration between the first time and the second time. Subsequently, the voltage is read out and a corresponding voltage signal by means of an analog-to-digital converter 6 digitized.

That in the 1 illustrated ultra wideband radar 1 is with multiple power sources 4 and several capacitors 5 formed, each power source 4 one capacitor each 5 assigned. So that several echo signals can be received and processed, all current sources are activated simultaneously with the emission of the pulse signal, so that all capacitors are charged simultaneously. Upon receipt of a plurality of successively subsequent echo signals, the current sources are deactivated / deactivated one after the other so that the different transit times of the received echo signals are stored in the respective capacitors.

That in the 1 illustrated ultra wideband radar 1 further includes a first counter 7 for counting the plurality of echo signals, wherein the first counter 7 is configured to assign each received echo signal to one of the plurality of current sources and capacitors, wherein the first counter is preferably set to zero when transmitting the pulse signal. Furthermore, the ultra-wideband radar includes 1 a comparator 8th , the each echo signal having a predetermined threshold 9 compares and generates a corresponding output signal and to the first counter 7 forwards. In this case, each echo signal via the comparator 8th digitized and then to an input of the first counter 7 forwarded. Each echo signal which is above the predetermined threshold 9 of the comparator 8th lies, generates a flank, which is the first counter 7 further overclocked. The threshold value is preferably designed to be adjustable and serves as an adjustable switching threshold for the comparator. Here, the switching threshold can be selected and set so that the echo detection is performed with maximum sensitivity and minimum error rate, drifts, offsets and temperature effects are corrected in the echo signals.

Preferably, with the transmission of a pulse signal, the first counter 7 reset for one measurement and the multiple power sources 4 activated simultaneously. After completion of a measurement and readout of the capacitors 5 these are discharged again and the radar is ready for the next measurement with the next pulse. The reset is done by means of a reset logic 13 generates a signal with which the first counter 7 via a reset input 14 is triggered / reset when transmitting each transmit pulse.

Also includes in the 1 illustrated ultra wideband radar 1 an overflow device 10 which is configured to output an overflow signal when more echo signals are received than there are capacitors. In this case, an overflow signal is generated which initiates measures to increase and / or shift the measuring range of the radar accordingly. For example, this can be a delay device 11 be provided, which is configured to provide a variable, time delay after the emission of the electromagnetic pulse signal and before charging the capacitors, so that the capacitors are charged only after the time delay, ie at a later date, and so the measuring range of the radar for distance measurement shifts to greater distances. In this case, in particular, the connection between the comparator and the first counter by means of at least one switch 12 switchable executed. Also, in this case another, second counter can be provided and connected. If the second counter is fed by a reference clock source, a variable delay between the transmission of the pulse signal and the counting of the first echo signals can thus be set. If the second counter is fed by the comparator output, a variable number of first objects can be hidden.

wobei
c die Lichtgeschwindigkeit in Luft ist. 2 shows a schematic representation of the operation of an ultra-wideband radar 1 as it is for example in the 1 is shown and described. The ultra broadband radar 1 sends temporally short and powerful impulses 20 out. The emitted impulses 20 be from an object 21 reflected and back to the ultra broadband radar 1 sent and there as echo signals 30 receive. Between sending the pulses 20 there is a break .DELTA.T , also called Tastpause. The distance D1 . D2 the reflective objects 21 will be over the term .delta.t (for a fixed radar). the period .delta.t denotes the time that elapses between the emission of an electromagnetic pulse signal 20 and receiving 33 an echo signal 30 elapses. The emission of an electromagnetic pulse signal 20 will be the first time t ₁ , the receiving 33 a first echo signal 30 at the second time t ₂ , the receiving 33 a second echo signal 30 at a third time t ₂ , etc. executed. The distance or the distance D1 between ultra wide band radar 1 and the first object 21 calculated, for example, according to the following formula: $$\text{D1}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\text{c}*{\text{t}}_1.$$

in which
c is the speed of light in air.

3 shows a schematic flow diagram for a possible embodiment of a method for measuring the distance of an object with an ultra-wideband radar, as beispielswese in the 1 and / or 2 is shown and described. The method comprises the following steps, namely first the transmission 31 an electromagnetic pulse signal at a first time and the simultaneous activation 32 a power source, so that a capacitor is charged. The activation 32 The power source is doing simultaneously with the emission at the first time t ₀ executed. After the emitted pulse signal has been reflected by an object back towards the ultra-wideband radar, an echo signal is transmitted by means of a receiver unit of the radar at the second time t ₁ receive 33 , Simultaneously with receiving the echo signal, the current source is deactivated and a voltage signal of the capacitor at the second time t ₁ detected 34 , Subsequently, the detected voltage signal is converted into a digital signal by means of an analog-to-digital converter 35 and can be processed in further digital steps 36 ,

LIST OF REFERENCE NUMBERS

1

UWB radar

2

transmitter unit

3

receiver unit

4

Power source (s)

5

Condenser (s)

6

Analog to digital converter

7

First counter

8th

comparator

9

threshold

10

Overflow device

11

delay means

12

switch arrangement

13

Reset logic

14

Reset input of the first counter 7

20

Electromagnetic pulse signal

21

object

30

echo signal

31

Emitting the electromagnetic pulse signal 20

32

Activate the power source 4

33

Receiving the echo signal 30

34

Detecting the voltage signal for a capacitor 5

35

Converting the detected voltage signal

36

Further processing

t ₀

First time

t ₁

Second time

.DELTA.T

Tastpause between the electromagnetic pulse signals 20

.delta.t

time

dt

Variable time delay

t ₂ , ... t _n

at least a third time

D1

Removal of the first object 21

D2

Removal of the second object 21

Claims (13)

Ultra-wideband radar (1) for distance measurement, comprising the following features: - a transmitter unit (2) for emitting (31) an electromagnetic pulse signal (20) at a first time (to), - a receiver unit (3) for receiving (33) an echo signal (30) at a second time (t ₁ ) or at at least one further time (t ₂ , ... tn), - a plurality of n current sources (4), - a plurality of n capacitors (5) associated with the A plurality of n current sources (4) is electrically connected, and - an analog-to-digital converter (6) which is electrically connected to the plurality of n capacitors (5), wherein - each current source (4) is in each case a capacitor (5) - the n current sources (4) are each configured to start a charging of the respective associated capacitor (5) at the first time (t ₀ ) and upon receiving (33) a plurality of echo signals (30) for the second or at least one further time (t ₂ , ... t _n ) to be deactivated one after the other n, and - the analog-to-digital converter (6) is configured, for each of the received echo signals (30), a respective voltage signal of the respective capacitor (5) at the second time (t ₁ ) or at the respective further time (t ₂ ,. .. t _n ) to convert into a first or another digital signal, wherein the voltage signal in each case proportional to the time duration (.DELTA.t) between the first time (t ₀ ) and the second (t ₁ ) or the at least one further time (t ₂ , ... t _n ) is. Ultra-wideband radar (1) to Claim 1 , characterized in that the current sources (4) are designed to be controllable, wherein a charging current for the respective capacitor (5) is adjustable between 1 μA and 10 mA. Ultra-wideband radar (1) according to one of the preceding claims, characterized in that the capacitors (5) are designed to be controllable, wherein a respective capacitance between 0.01pF and 10pF is adjustable An ultra-wideband radar (1) as claimed in any one of the preceding claims, wherein a first counter (7) is provided for counting a plurality of echo signals (30) configured to associate each received echo signal with one of n current sources (4) and n capacitors (5). Ultra-wideband radar (1) to Claim 4 comprising at least one comparator (8), which compares each echo signal (30) with a predetermined threshold value (9) and generates a corresponding output signal and forwards it to the first counter (7). An ultra-wideband radar (1) according to any one of the preceding claims, comprising overflow means (10) configured to output an overflow signal when more than n echo signals are received. Ultra-wideband radar (1) according to one of the preceding claims, comprising a delay device (11) which is configured to provide a variable, time delay (dt) after the emission (31) of the electromagnetic pulse signal (20) and before charging the capacitor, so that the capacitor (5) is charged only after the time delay (dt) has elapsed at a later time (t ₀ + dt) and a measuring range for the distance measurement shifts. Ultra-wideband radar (1) to Claim 7 wherein the delay means (11) configured to provide a variable clock delay. Ultra-wideband radar (1) to Claim 7 or 8th additionally comprising a reference clock configured to set the variable time delay (dt) or the variable clock delay. An ultra-wideband radar (1) according to any one of the preceding claims, configured to emit the electromagnetic pulse signals (20) at a frequency of 10 kHz to several 10 GHz, preferably between 10 MHz to 200 GHz and even more preferably between 1 GHz to 100 GHz. Ultra-wideband radar (1) to Claim 10 which is configured to integrate a plurality of voltage signals of the same capacitor (5) in the distance measurement of a same object with a plurality of successive electromagnetic pulse signals (20). Method for distance measurement with an ultra-wideband radar (1) having a transmitter unit (2) and a receiver unit (3), the method comprising the following steps: - emitting (31) an electromagnetic pulse signal (20) with the transmitter unit (1) at a first Timing (to), - activating (32) a plurality of n current sources (4), so that one of the current sources (4) respectively associated capacitor (5) is charged from a plurality of n capacitors, wherein the activation (31) of the current sources (4) is executed simultaneously or with a variable time delay (dt) for transmitting (31) at the first time (t ₀ ) or at the time (to + dt), - receiving (33) a plurality of echo signals (30) with the receiver unit (3 ) at a second time (t ₁ ) or at at least one further time (t ₂ , ... t _n ), - detecting (34) a respective voltage signal of the respective capacitor (5) at the second time (t ₁ ) or at least another Time (t ₂ , ... t _n ) when the echo signals (30) are received respectively, and - converting (35) the respective detected voltage signals into a first or another digital signal by means of an analog-to-digital converter (6) , wherein the voltage signal is proportional to the time duration (Δt) between the first time (t ₀ ) and the second (t ₁ ) or the at least one further time (t ₂ , ... t _n ). Method according to Claim 12 for measuring the distance with an ultra-wideband radar (1) according to one of Claims 1 to 11 ,

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