Magnetic field pulse current sensing for timing sensitive circuits.

Abstract

The start time t of the current pulse passing through the current conductor START , end time t END , and / or peak time t MAX The current measurement circuit includes a pickup coil and a threshold crossing detector. The pickup coil detects a voltage V proportional to the magnetic field around the conductor. SENSE This magnetic field is proportional to the change in current over time. SENSE ' and the threshold voltage, and the transition time and V SENSE The current measurement circuit may also include an integrator and a sample-and-hold circuit. The integrator may generate an output signal that indicates whether the slope of V' is positive or negative. SENSE ' over time, and the integrated signal V SENSE The sample and hold circuit generates V SENSE A MAX and generating a second output signal that can be used to measure the pulse current.

Description

[Technical field]

[0001] The present invention relates generally to current measurement circuits based on magnetic field sensing, and more particularly to current measurement circuits for determining the start and end times of a current pulse. [Background technology]

[0002] In many applications of pulsed current generators, the output current pulse must meet certain specifications, such as precise start and end times, as well as maximum or minimum current values. For example, in a time-of-flight (ToF) light detection and ranging (lidar) system for autonomous vehicles, a pulsed current generator serves as a laser driver. The time delay between the transmission of a laser pulse and the detection of its reflection can be used to determine the distance between the laser and an object in the environment. Since the speed of light is 30 centimeters (cm) per nanosecond (ns), short laser pulses are advantageous when distance measurement resolution requirements are stringent. As an example, for centimeter-scale resolution, the laser pulse width is often on the order of a few ns to tens of ns, and the time delay of the reflection from a nearby object can be only a few ns.

[0003] Therefore, ToF lidar systems must be able to precisely determine the start and end times of the laser pulse to within 1 ns, often with an accuracy of 100 picoseconds (ps) or less, in order to accurately determine the laser pulse width and the time delay between the transmission of the laser pulse and the detection of its reflection. The performance of a ToF lidar system is also affected by the amplitude of the laser pulse, and as the pulse amplitude increases, its reflection becomes detectable after traveling longer and longer distances. However, the maximum amplitude of the laser pulse must comply with eye safety regulations, and the laser driver must limit the peak amplitude of the current pulse accordingly. It is therefore advantageous to transmit the laser pulse at the maximum amplitude that satisfies safety considerations.

[0004] Many pulsed current generators include feedback systems to measure the output current pulse and make appropriate adjustments. These feedback systems include a current measurement circuit and a controller for the pulsed current generator. The current measurement circuit generates a signal, typically in the form of a voltage, proportional to the current being measured. From this signal, the start and end times of the current pulse and the peak amplitude of the current pulse can be determined, which are used by the controller to adjust the parameters of the current pulse generator. However, the output current pulse can be on the order of tens to hundreds of amperes (A) in some applications, which makes the current sensing more complex. When very short pulses, such as the aforementioned ns pulses, are required, the parasitic effects of the current sensing circuit can be detrimental to the operation of the driver.

[0005] FIG. 1 shows a schematic diagram of a conventional current measurement circuit 100 using a shunt resistor 120. A pulse generator 110 generates a current pulse I PULSE which is supplied to the load 130 through the shunt resistor 120. SHUNT is given, then according to Ohm's law, the voltage V SHUNT To reduce the effect of the shunt resistor on the pulse generator, SHUNT is usually very small, on the order of milliohms (mΩ). As a result, V SHUNT The value of is small, and therefore often a differential amplifier 140 is connected to the terminals of the shunt resistor 120 to generate an amplified voltage V SENSE This outputs I PULSE In some applications, short pulses impose stringent demands on the amplifier 140, such as high bandwidth.

[0006] R in mΩ SHUNTEven with this, very large amplitude current pulses can cause the shunt resistor 120 to lose large amounts of power as heat, which can damage other components on the circuit or unnecessarily strain the system power supply or battery. Additionally, as the shunt resistor 120 heats up, it can experience thermal drift, changing its resistance and V SENSE changes, which may require computationally expensive compensation to precisely determine the start and end times and peak amplitude of the current pulse. PULSE directly, which means that a shunt resistor 120 is placed in the main driver signal chain, which disadvantageously increases the inductance of the main driver circuit.

[0007] Some current measurement circuits avoid the power losses and increased inductance associated with shunt current measurements by indirectly measuring the current pulse through the resulting magnetic induction or magnetic flux density. The magnetic flux density induced by a current through a conductor can be measured by a Hall effect sensor, a fluxgate sensor, a magnetoresistor, or a giant magnetoresistor, among others. Figures 2A-2B show the current pulse I PULSE 2A shows the placement of a Hall sensor 220 relative to a current conductor 210 conducting I, and a schematic diagram of a conventional current measurement circuit 200 using the Hall sensor 220. In FIG. PULSE The Hall sensor 220 is disposed in the vicinity of the current conductor 210 such that changes in magnetic flux density around the current conductor 210 caused by the change in magnetic flux density are detected by the Hall sensor 220.

[0008] In FIG. 2B, the Hall sensor 220 outputs a voltage to a high gain amplifier 240. The high gain amplifier converts the small output voltage from the Hall sensor 220 into a larger voltage V SENSE This voltage is amplified to V SENSE I PULSEThe Hall sensor 220, and other current sensing methods based on magnetic flux density, is proportional to the magnetic flux density around the conductor 210 due to the magnetic field. However, the Hall sensor 220, and other current sensing methods based on magnetic flux density, rely on semiconductor materials that are subject to thermal drift or exhibit nonlinear behavior. Both thermal drift and nonlinear behavior require active circuitry to recalibrate and compensate for changes in device characteristics and to analyze the nonlinear response. Furthermore, the majority of active circuits required for Hall sensors have stringent requirements for high bandwidth, especially for short pulse applications, similar to those imposed on the differential amplifier 140 shown in FIG. 1.

[0009] Some current measurement circuits attempt to avoid some of the active circuit requirements associated with measuring current pulses through magnetic induction by instead measuring the rate of change of magnetic flux, i.e., the magnetic field. The magnetic field may be measured, for example, by a current transformer or Rogowski coil. A current transformer includes a magnetic core around which a secondary winding is disposed. The magnetic core may saturate at high currents, increasing the inductance of the system, thereby affecting the operation of other components. Some magnetic cores with high permeability have high saturation flux density, but poor high frequency response.

[0010] A Rogowski coil does not contain a magnetic core and is therefore not subject to saturation and can have a large bandwidth, but can otherwise be considered a current transformer with a small magnetizing inductance and an approximately open circuit burden at the winding terminals. Figure 3 shows a schematic diagram of a conventional current measurement circuit 300 using a Rogowski coil 320. The Rogowski coil 320 detects a current pulse I PULSE The Rogowski coil 320 comprises a helical coil disposed around a conductor 310 conducting I with a lead 330 from one end of the coil passing through the center of the coil to the other lead 340. The leads 330 and 340 are connected to an integrator 350 which integrates the output of the Rogowski coil 320 over time to obtain I PULSE Voltage V proportional to SENSE get.

[0011] Both Rogowski coils and current transformers use an I PULSE The current transformer is a current-transducing element that surrounds the conductors that conduct the current. However, the need for surrounding conductors makes it difficult to build a semiconductor die that contains a Rogowski coil or a current transformer. In particular, current transformers can occupy a large area of ​​the semiconductor die, which is a disadvantage in, for example, lidar systems where the laser diodes and their drivers are located close to each other and precisely aligned to simplify alignment of optical elements such as lenses. Similarly, integrating a Rogowski coil on a printed circuit board would involve multiple layers of the board and require a large number of vias. Summary of the Invention [Means for solving the problem]

[0012] The present invention addresses the drawbacks of power loss, increased inductance in the main driver circuit, active circuitry, large area, and complex construction discussed above by providing a current measurement circuit with a pick-up coil that does not need to surround the current conductor. More specifically, the present invention comprises a pick-up coil and at least one threshold crossing detector, as described herein. The pick-up coil generates a voltage proportional to a magnetic field around the current conductor, which magnetic field is proportional to the change in current through the current conductor over time. The threshold crossing detector compares the voltage proportional to the magnetic field with at least one threshold voltage, and based on the comparison, generates an output signal indicative of the transition time of the current pulse (e.g., start time, end time, or peak amplitude time) and whether the slope of the voltage proportional to the magnetic field over time is positive or negative based on the selected threshold voltage.

[0013] In a further embodiment, the current measurement circuit also includes an integrator and a sample and hold circuit. The integrator integrates over time a voltage proportional to the magnetic field and generates an integrated signal based on the integrated voltage, the resulting signal being proportional to the current to be measured. The sample and hold circuit is triggered by a signal indicative of the peak amplitude time.

[0014] In a further embodiment, the pick-up coil is a single loop configured to be placed near a current conductor and can be monolithically integrated on a single semiconductor chip. In a further embodiment, the pick-up coil can have one or more turns configured to increase the total magnetic flux resulting from the current to be measured through the coil and reduce the total magnetic flux from other sources. In another embodiment, a portion of the pick-up coil is integrated on a semiconductor chip with at least one threshold crossing detector, the portion of the pick-up coil being formed by the die terminals and the outer conductor. The outer conductor can be part of a mounting substrate, such as a printed circuit board, that includes the current conductor.

[0015] These and other preferred features described herein, including various novel details of implementation and combinations of elements, will now be described in more detail with reference to the accompanying drawings and set forth in the claims. It is to be understood that the specific methods and apparatus are shown for illustrative purposes only and not as limitations on the scope of the claims. As will be appreciated by those skilled in the art, the principles and features of the teachings herein can be employed in numerous and varied embodiments without departing from the scope of the claims.

[0016] The features, objects, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a conventional current measurement circuit using a shunt resistor. [Figure 2A] FIG. 2 is a diagram showing the arrangement of a Hall sensor relative to a current conductor. [Figure 2B] FIG. 1 is a schematic diagram of a conventional current measurement circuit using a Hall sensor. [Diagram 3] FIG. 1 is a schematic diagram of a conventional current measurement circuit using a Rogowski coil. [Figure 4A] 4 is a graph of the voltage output from a conventional current measurement circuit, such as the circuit shown in FIGS. 1-3, resulting from current pulses having the same general shape; [Figure 4B] 4 is a graph of the derivative of the aforementioned voltage output. [Diagram 5] FIG. 2 illustrates a current measurement circuit according to one embodiment of the present invention. [Figure 6] FIG. 2 shows a current measurement circuit according to an embodiment of the invention, partially integrated with the remainder of the pick-up coil formed by the die terminals and an outer conductor which may form part of a mounting substrate such as a printed circuit board. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the following detailed description, reference will be made to several embodiments. These embodiments will be described in sufficient detail to enable those skilled in the art to practice them. It will be understood that other embodiments may be utilized, and that various structural, logical, and electrical changes may be made. The combinations of features disclosed in the following detailed description may not be necessary to practice the teachings in their broadest sense, and such combinations of features are instead merely taught to describe particularly representative examples of the present teachings.

[0019] 4A shows a graph of the voltage output from a conventional current measurement circuit, such as the circuits shown in FIGS. 1-3, and FIG. 4B shows the derivative of the voltage output from a conventional current measurement circuit. Graph 400 shows the output voltage V over time from a conventional current measurement circuit.SENSE where V SENSE is the current pulse I PULSE is substantially proportional to the current pulse I PULSE Start time t START and end time t END To identify the V SENSE to a given threshold V REF Compared to V SENSE V REF In response to an increase above the starting time t START * Also V SENSE V REF In response to a decrease below the end time t END * As shown in graph 400, a half-sine wave V SENSE has a gentler slope than a square wave, and t START After a certain time period from t END Only some time period before V REF It cannot change higher or lower.

[0020] Therefore, the inaccurate t START * and t END * However, they introduce errors into calculations using them, such as distance calculations based on the time delay between transmitting a laser pulse and detecting its reflection from the environment. START * and t END * The accuracy of I PULSE , and hence I PULSE Additional calculations are required to compensate for the change in peak amplitude of t START and t END This method for identifying V SENSE This can be acceptably accurate when is a rectangular pulse, but V SENSE When is a non-rectangular pulse such as a half sine wave, the required accuracy of less than 1 ns cannot be met.

[0021] IPULSE t START or t END To more accurately and consistently identify V, some systems use SENSE The time derivative of V SENSE ' is calculated, and this V SENSE ' has V SENSE Due to the change in the slope of I PULSE t START From scratch, PULSE t END Then, in those systems, there is a sharp increase in the derivative V SENSE ', another predefined threshold V REF2 I am comparing it with PULSE t START and t END V in SENSE A dramatic change in the value of ' occurs at the identified start time t START * and end time t END * Reduce the error of I PULSE and V REF2 Removes the dependency on the chosen value of V. REF2 is set to zero, so that I PULSE The time t MAX However, the system can also determine the derivative V SENSE ', V SENSE Noise on the input signal is accentuated and often requires filtering to reduce this noise. The introduction of noise and additional filtering steps further complicate the system and reduce its performance and accuracy. The process of identifying when a threshold is crossed and the sign of the slope of the crossing is known by various terms such as edge detection, zero crossing detection, and threshold crossing detection. It is generally implemented using a combination of comparators and digital logic circuits. Such circuits and methods are generally recognized by those skilled in the art.

[0022] 5 shows a current measurement circuit 500 according to one embodiment of the present invention. A pickup coil 520 detects a current pulse I PULSE is disposed near a conductor 510 conducting I PULSE The pickup coil 520 detects the time-varying magnetic field induced by I. The leads 524 and 528 are loaded with an impedance much larger than the coil impedance in the frequency band of interest, so that the voltage on the leads 524 and 528 is proportional to the derivative of the magnetic field strength, which itself is I. PULSE The voltage at leads 524 and 528 is proportional to the derivative V SENSE ', which may be amplified by an optional amplifier 530 or output directly, and this derivative V SENSE 'I PULSE is proportional to the derivative of

[0023]

number

[0024] where K is the area of ​​the loop, the number of turns, or I PULSE is a constant that depends on the characteristics of the pickup coil 520, such as the position of the turn relative to the conductor 510 that conducts the current.

[0025] V from leads 524 and 528, or from the output of optional amplifier 530 SENSE ' is fed to a threshold crossing detector 540, which in turn receives a reference voltage V REF2 and generates an output signal 550. REF2 By appropriately setting START , t END , or t MAX The current measurement circuit 500 can also show that t START and t END To digitally calculate VSENSE It also avoids the area, power consumption, and component costs associated with high speed analog-to-digital converters for sampling the .

[0026] In some embodiments of the present invention, an integrator 560 is used to SENSE ', and thus V SENSE , and other calculations, i.e.

[0027]

number

[0028] In this example, V SENSE is fed to a sampler or sample-and-hold circuit 570, which receives t (from output 550) MAX and generates an output signal 580 that can be used to measure the pulse current.

[0029] The pickup coil 520 does not include a magnetic core and can be a Rogowski coil. PULSE For I, the resulting magnetic field is so large that fewer turns and a smaller loop area, or even a single loop in close proximity to the conductor 510, may be sufficient to detect the magnetic field. PULSE The magnetic field in this case is I PULSEThe pickup coil 520 is much larger than the magnetic field for currents other than 100 MHz or ambient magnetic fields, so that errors introduced by other magnetic fields are negligible, and the pickup coil 520 does not need to surround the conductor 510. The turn or turns of the pickup coil may be configured to maximize the total magnetic flux resulting from the current in the conductor 510 to be measured throughout the coil while minimizing the total magnetic flux from other sources. Because the pickup coil 520 does not contain a magnetic core, the pickup coil 520 does not saturate at high currents or suffer from bandwidth limitations based on the dielectric constant of the magnetic core. The pickup coil 520 also avoids the thermal drift associated with semiconductor components such as Hall sensors and shunt resistors.

[0030] The pickup coil 520 can be monolithically integrated on a semiconductor die because it may have a smaller loop area and fewer turns than a Rogowski coil and does not need to encircle the conductor 510. Similarly, the pickup coil 520 can be placed in a strategic location near the load or bus capacitor. In addition, the current measurement circuit 500 is separated from the main driver signal chain and adds negligible impedance to the main driver circuit, and therefore the current measurement circuit 500 does not substantially affect the operation of the main driver circuit. Separating the current measurement circuit 500 from the main driver circuit allows the current measurement circuit 500 to sense both positive and negative currents even in circuits with zero volt minimum supply voltages, thereby providing a high-level reference for the V SENSE ' zero crossing detection becomes easy.

[0031] 6 shows a portion 600 of a current measurement circuit similar to current measurement circuit 500, according to one embodiment of the invention. An integrated circuit die 640 is connected to another substrate, such as a mounting substrate, by terminals, such as terminal 650. Integrated circuit die 640 includes the remaining portions of the current measurement circuit, such as an integrator, a threshold crossing detector, and a sample and hold circuit. Portion 600 includes a portion of a pick-up coil 620 formed by die terminals 624 and 628 and an outer conductor 626, which may be part of the mounting substrate. The mounting substrate, including conductor 626, also couples current pulses I PULSE The integrated circuit die 640 may include a conductor 610 that conducts a current. The terminals of the pickup coil 620 may be within the integrated circuit die 640 itself and may be connected to the remainder of the current measurement circuitry.

[0032] The above description and drawings should be considered as merely illustrative of specific embodiments that achieve the features and advantages described herein. Modifications and substitutions can be made to specific process conditions. Therefore, the embodiments of the present invention should not be considered as limited by the above description and drawings. [Explanation of symbols]

[0033] 100 Current measurement circuit 110 Pulse Generator 120 Shunt resistor 140 Differential Amplifier 200 Current measurement circuit 210 Current Conductor 220 Hall Sensor 300 Current measurement circuit 310 Conductor 320 Rogowski Coil 330 Lead Wire 340 Lead Wire 350 Integrator 400 graphs 450 graphs 500 current measurement circuit 510 Conductor 520 Pickup coil 524 Lead Wire 528 Lead Wire 530 Optional Amplifier 540 Threshold Crossing Detector 550 Output signal, output 560 Integrator 570 Sampling or sample-hold circuit 580 Output Signal 600 pieces 610 Conductor 620 Pickup coil 624 Die Terminal 626 Outer conductor 628 Die Terminal 640 Integrated Circuit Dies 650 Terminal I PULSE Current Pulse R SHUNT Shunt Resistance Value V SHUNT Voltage t END End time t END * End time t MAX Peak hours t START Start time t START * Start time V REF A given threshold V REF2 Another predetermined threshold, the reference voltage V SENSE Output voltage, half sine, integral signal V SENSE ' Derivative, voltage

Claims

1. 1. A current measurement circuit for measuring a characteristic of a current pulse passing through a current conductor, comprising: A voltage V proportional to the derivative with respect to time of the magnetic field around the current conductor SENSE a pick-up coil for generating a magnetic field, said magnetic field being proportional to the current passing through said current conductor; Two leads connected to the pickup coil; An amplified V connected to the pickup coil via the two leads SENSE ' to generate V SENSE an amplifier for amplifying the The amplified V SENSE at least one threshold crossing detector for comparing a time (t MAX ), and at least one threshold crossing detector that indicates whether the slope of V SENSE ' is positive or negative; Without using a circuit to calculate the derivative of the voltage output, V SENSE ' over time, and an integrated signal V is generated based on the integrated voltage. SENSE an integrator for generating The peak amplitude time (t MAX ) in SENSE and a sample and hold circuit for sampling the current and generating a second output signal that can be used to measure the current pulse. A current measurement circuit comprising:

2. 2. The current measurement circuit of claim 1, wherein the reference threshold voltage is ground.

3. 10. The current measurement circuit of claim 1, wherein the pickup coil comprises a single loop configured to be placed in proximity to the current conductor.

4. 2. The current measurement circuit of claim 1, wherein the pickup coil is configured so as not to surround the current conductor.

5. 10. The current measurement circuit of claim 1, wherein the pickup coil comprises a Rogowski-type coil.

6. 10. The current measurement circuit of claim 1, integrated on a single semiconductor chip.

7. The current measurement circuit of claim 6 , wherein the single semiconductor chip further comprises the current conductor.

8. 2. The current measurement circuit of claim 1, wherein the at least one threshold crossing detector and the first portion of the pickup coil are integrated on a semiconductor chip, and the second portion of the pickup coil is formed by at least two die terminals and an outer conductor.

9. 9. The current measurement circuit of claim 8, wherein the outer conductor is part of a mounting board.

10. The current measurement circuit of claim 9 , wherein the mounting substrate further comprises a portion of the current conductor.

Images