Resistance detection method and resistance detection circuit

Abstract

The invention discloses a resistance value detection method and a resistance value detection circuit, and the method comprises the steps: obtaining a test voltage and a reference voltage, setting one of the test voltage and the reference voltage as a to-be-compared value, setting the other one as a fixed reference value, and enabling the to-be-compared value to comprise a first boundary value and a second boundary value; respectively comparing the first boundary value and the second boundary value with a reference value to obtain a first comparison result and a second comparison result; the resistance value range of the resistance value of the tested unit is calculated according to the first comparison result and the second comparison result, the test voltage is a voltage value obtained by applying the test current to the tested unit, and the reference voltage is a voltage value generated by the reference voltage providing circuit. According to the resistance value detection method and the resistance value detection circuit, the resistance value range can be obtained according to the boundary value and the reference value provided by the low-voltage circuit, the resistance value detection precision is improved, the use of high-voltage devices is reduced, the circuit occupied area is reduced, and the cost is reduced.

Description

Technical Field

[0001] This application relates to the field of electronic circuit technology, specifically to a resistance detection method and a resistance detection circuit. Background Technology

[0002] Power over Ethernet (PoE), also known as remote power supply equipment, is divided into power sourcing equipment (PSE) and powered devices (PD).

[0003] Figure 1 A schematic block diagram of a PoE power supply system according to the prior art is shown. Figure 1 As shown, the Power over Ethernet (PoE) system may include a Power Provider Interface (PSE) device (not shown) and a Power Receiver (PD) device. The PSE device is connected to the PD device's power receiving port via a network transformer and an Ethernet twisted-pair cable 20. Figure 1 In the circuit 10, the receiving end circuit includes a rectifier circuit 5, a detection resistor 6, and a switching circuit 7. Typically, in a PoE system, the characteristic impedance of the PD receiving end is an impedance network consisting of a rectifier diode and a characteristic resistor connected in series. When the PSE and PD devices are connected, the PSE power supply chip needs to detect the characteristic impedance resistance of the PD receiving end. Only when the detected characteristic impedance value meets the protocol standard will the receiving end be considered a PoE compliant device, and power will be supplied to it. Traditional PSE chips use either applying different voltage signals to the PD device port and detecting the corresponding current information, or applying different current signals to the PD device port and detecting the voltage information, ultimately calculating the characteristic impedance value using the formula R=ΔV / ΔI.

[0004] Since PoE systems are high-voltage power supply systems, traditional technologies require the design of high-voltage-resistant circuits to apply voltage or current to the PD receiver, detect voltage and current information, sample voltage and current, and perform calculations. This necessitates the use of high-voltage operational amplifiers, high-voltage sampling circuits, ADCs, and computational circuits, which often consume significant circuit area, leading to high chip costs. Furthermore, the common resistance calculation method is relatively simple, has a limited applicability, and is inaccurate in resistance detection. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a resistance detection method and a resistance detection circuit to solve the problems in the prior art.

[0006] According to an aspect of the present application, a resistance value detection method for detecting a resistance value of a unit under test is provided, wherein the resistance value detection method comprises: obtaining a test voltage and a reference voltage, one of which is set as a value to be compared and the other is set as a reference value with a fixed value, the value to be compared comprising a first boundary value and a second boundary value; comparing the first boundary value and the second boundary value with the reference value respectively to obtain a first comparison result and a second comparison result; and calculating a resistance value range to which the resistance value of the unit under test belongs according to the first comparison result and the second comparison result, wherein the test voltage is a voltage value obtained by applying a test current to the unit under test, and the reference voltage is a voltage value generated by a reference voltage providing circuit.

[0007] Optionally, the test voltage is the value to be compared, the reference voltage is the reference value, and obtaining the test voltage and the reference voltage comprises: setting a minimum resistance value and a maximum resistance value, obtaining a test current upper limit value and a test current lower limit value according to the minimum resistance value and the maximum resistance value respectively; applying the test current upper limit value and the test current lower limit value to the resistance of the unit under test respectively to obtain the first boundary value and the second boundary value correspondingly; and setting a resistance reference value, and obtaining the reference voltage with a fixed value according to the resistance reference value as the reference value.

[0008] Optionally, the test voltage is the reference value, the reference voltage is the value to be compared, and obtaining the test voltage and the reference voltage comprises: setting a minimum resistance value and a maximum resistance value, obtaining a reference voltage lower limit value and a reference voltage upper limit value according to the minimum resistance value and the maximum resistance value respectively, and taking the reference voltage lower limit value and the reference voltage upper limit value as the first boundary value and the second boundary value respectively; and applying a set current reference value to the resistance of the unit under test to obtain the test voltage with a fixed value as the reference value.

[0009] Optionally, if the resistance value range calculated according to the first comparison result and the second comparison result is not within a resistance value interval formed by the minimum resistance value and the maximum resistance value, the value to be compared is reset.

[0010] Optionally, the resistance value detection method further comprises: adjusting the first boundary value and the second boundary value according to the first comparison result, the second comparison result and a detection precision, so as to update the resistance value range until the resistance value range reaches the detection precision, wherein each time the first boundary value and the second boundary value are adjusted, the interval value range bounded by the first boundary value and the second boundary value is reduced.

[0011] Optionally, adjusting the first boundary value and the second boundary value comprises adjusting the test current applied to the unit under test to adjust the first boundary value and the second boundary value, or adjusting the voltage value generated by the reference voltage providing circuit to adjust the first boundary value and the second boundary value.

[0012] Optionally, the test voltage is the value to be compared, the reference voltage is the reference value, and the stepwise adjustment of the first boundary value and the second boundary value according to the first comparison result, the second comparison result, and the detection precision to update the resistance range until the resistance range reaches the detection precision comprises: if the first comparison result is that the first boundary value is greater than the reference value each time, stepwise decreasing the upper limit value of the test current until the first boundary value is less than the reference value; if the second comparison result is that the second boundary value is less than the reference value each time, stepwise increasing the lower limit value of the test current until the second boundary value is greater than the reference value; and if the resistance range obtained according to the first comparison result and the second comparison result reaches the detection precision, stopping the adjustment of the first boundary value and the second boundary value.

[0013] Optionally, the test voltage is the reference value, the reference voltage is the value to be compared, and the stepwise adjustment of the first boundary value and the second boundary value according to the first comparison result, the second comparison result, and the detection precision to update the resistance range until the resistance range reaches the detection precision comprises: if the first comparison result is that the first boundary value is less than the reference value each time, stepwise increasing the lower limit value of the reference voltage until the first boundary value is greater than the reference value; if the second comparison result is that the second boundary value is greater than the reference value each time, stepwise decreasing the upper limit value of the reference voltage until the second boundary value is less than the reference value; and if the resistance range obtained according to the first comparison result and the second comparison result reaches the detection precision, stopping the adjustment of the first boundary value and the second boundary value.

[0014] Optionally, the unit under test is a powered device, and if the resistance range is within a resistance range specified by a protocol, it is determined that the impedance of the powered device meets the standard of the protocol.

[0015] According to another aspect of the present application, there is provided a resistance detection circuit connected to a unit under test, for detecting a resistance of the unit under test, wherein the resistance detection circuit comprises: a test current providing unit for applying a test current to the unit under test to generate a test voltage; a test voltage obtaining unit for obtaining the test voltage across the unit under test; a comparison unit for obtaining a reference voltage generated by a reference voltage providing circuit, taking one of the test voltage and the reference voltage as a comparison value and the other as a reference value with a fixed value, the comparison value comprising a first boundary value and a second boundary value, and comparing the first boundary value and the second boundary value with the reference value respectively to obtain a first comparison result and a second comparison result; and a resistance control unit for calculating a resistance range to which the resistance of the unit under test belongs according to the first comparison result and the second comparison result.

[0016] Optionally, the resistance control unit further adjusts the first boundary value and the second boundary value according to the first comparison result, the second comparison result and a detection precision to update the resistance range until the resistance range reaches the detection precision, wherein each time the first boundary value and the second boundary value are adjusted, the range of the interval bounded by the first boundary value and the second boundary value is reduced.

[0017] Optionally, the resistance control unit adjusts the first boundary value and the second boundary value by adjusting the test current generated by the test current providing unit, or adjusts the first boundary value and the second boundary value by adjusting a voltage value generated by the reference voltage providing circuit.

[0018] Optionally, the test voltage is the comparison value, the reference voltage is the reference value, the test current providing unit obtains a test current upper limit value and a test current lower limit value according to a preset minimum resistance value and a preset maximum resistance value respectively, and applies the test current upper limit value and the test current lower limit value to the resistance of the unit under test to obtain the first boundary value and the second boundary value respectively; and the reference voltage providing circuit obtains the reference voltage with a fixed value as the reference value according to a preset resistance reference value.

[0019] Optionally, the test voltage is the reference value, the reference voltage is the comparison value, the reference voltage providing circuit obtains a reference voltage lower limit value and a reference voltage upper limit value according to a preset minimum resistance value and a preset maximum resistance value respectively, and takes the reference voltage lower limit value and the reference voltage upper limit value as the first boundary value and the second boundary value respectively; and the test current providing unit applies a set current reference value to the resistance of the unit under test to obtain the test voltage with a fixed value as the reference value.

[0020] Optionally, the comparison unit comprises at least one comparator, when the comparison unit comprises only one comparator, the comparator receives the first boundary value and the second boundary value in time division.

[0021] The resistance detection method and the resistance detection circuit provided by the application can obtain a test voltage by applying a test current to the unit to be detected, and then obtain a reference voltage from a reference voltage supply circuit. One of the test voltage and the reference voltage is set as a variable value and the other is set as a fixed value. The comparison unit compares the two different variable values (the first boundary value and the second boundary value) with the same fixed value, and generates a resistance range according to the comparison result. Therefore, different resistance ranges with different accuracies can be obtained by setting different reference voltages or test currents, the resistance value can be detected in multiple ranges and tested with high accuracy, and the application scenarios are wide and the resistance value is accurate. Correspondingly, the resistance detection circuit for implementing the resistance detection method takes the comparison unit as the core circuit, the circuit structure is simple, the occupied area is small, and the cost of the detection circuit is greatly reduced. Moreover, the comparison unit can be provided with only one comparator, and the comparator is time-division multiplexed, that is, the first boundary value and the second boundary value are received in time division to be compared respectively, so that the resistance detection circuit only needs one high-voltage comparator, the use of a large number of high-voltage devices is avoided, the circuit structure is simple, and the safety is high.

[0022] Further, the sizes of the first boundary value and the second boundary value set according to the comparison result can be adjusted step by step, so that the first boundary value and the second boundary value are continuously close to each other, and the measured resistance range is continuously reduced, and gradually approaches the minimum range meeting the detection accuracy. That is, by continuously adjusting step by step, the resistance value detected reaches the minimum detection accuracy, and the accuracy and reliability of the resistance detection are improved.

[0023] Further, the resistance detection method and the resistance detection circuit can be applied in impedance detection of a PD device, and by switching different reference voltages or test currents, the comparison result of the comparison unit is used to judge whether the impedance of the PD powered end meets the protocol standard, which is fast, efficient and accurate.

[0024] It should be noted that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the application. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 a schematic block diagram of a POE power supply system according to the prior art is shown;

[0026] Figure 2 a schematic block diagram of a resistance detection circuit according to an embodiment of the application is shown;

[0027] Figure 3A schematic flow chart of a resistance detection method according to an embodiment of the present application is shown.

[0028] Figure 4 A schematic circuit diagram of a resistance detection circuit according to a first embodiment of the present application is shown.

[0029] Figure 5 A schematic circuit diagram of a resistance detection circuit according to a second embodiment of the present application is shown. DETAILED DESCRIPTION

[0030] For the purpose of facilitating the understanding of the present application, a more complete understanding of the present application will be provided in the following with reference to the relevant drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be realized in different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0031] In the embodiments of the present application, a resistance detection circuit is provided, which can perform a subsequent resistance detection method to obtain an accurate resistance range of a measured unit. The resistance detection circuit can be applied in a PSE power supply system to detect the characteristic impedance of a PD powered device end. The resistance detection method and the resistance detection circuit will be described in detail below in combination with Figures 2-4 The resistance detection method and the resistance detection circuit of the present application will be described in detail.

[0032] Figure 2 A schematic block diagram of a resistance detection circuit according to an embodiment of the present application is shown. The present application provides a resistance detection circuit 200 for detecting the resistance of a measured unit 100. The measured unit 100 can be any circuit whose resistance needs to be detected, and the characteristic resistance is represented by R. When it is applied in the load impedance detection of a POE system, the measured unit 100 can be a PD device (powered device), for example, to detect the characteristic impedance value of the equivalent resistance of the PD device. The resistance detection circuit is used to perform Figure 3 The resistance detection method in the described embodiments.

[0033] As Figure 2As shown, the resistance detection circuit 200 of the embodiment includes a test current providing unit 210, a test voltage obtaining unit 220, a comparison unit 230 and a resistance control unit 240. The test current providing unit 210 applies a test current II to the unit 100 under test to generate a test voltage VI on the unit 100 under test, and the test voltage VI is obtained from both ends of the unit 100 under test by the test voltage obtaining unit 220. The comparison unit 230 is configured to obtain a reference voltage Vref generated by a reference voltage providing circuit (not shown in the figure) and to obtain the test voltage VI. One of the test voltage VI and the reference voltage Vref is taken as a comparison value, and the other is taken as a reference value with a fixed value. The comparison value includes a first boundary value and a second boundary value, and the comparison unit 230 compares the first boundary value and the second boundary value with the reference value respectively to obtain a first comparison result and a second comparison result. The comparison unit 230 includes at least one comparator, i.e. the comparison unit 230 can be provided with at least one comparator, and of course, two or more comparators can also be provided. When only one comparator is provided, the comparator receives the first boundary value and the second boundary value in time division manner, and compares them with the reference value respectively to obtain the first comparison result and the second comparison result. The resistance control unit 240 calculates a resistance range Rx1-Rx2 to which the resistance of the unit 100 under test belongs according to the first comparison result and the second comparison result. The first boundary value and the second boundary value form an interval range, and the corresponding resistance range is detected.

[0034] In a feasible embodiment, the test voltage VI is the comparison value, and the reference voltage Vref is the reference value, i.e. the reference voltage Vref is a fixed value set in advance, for example, the reference voltage providing circuit obtains the reference voltage Vref with a fixed value as the reference value according to a preset resistance reference value RT. The test voltage VI can take two values, corresponding to the first boundary value and the second boundary value respectively. At this time, the test current providing unit 210 obtains a test current upper limit value and a test current lower limit value according to a preset minimum resistance value Rmin and a maximum resistance value Rmax respectively. The test current upper limit value and the test current lower limit value are applied to the resistance of the unit 100 under test respectively, and the detection voltage is obtained to correspond to the first boundary value and the second boundary value. Then the detection voltage is a voltage value related to the resistance of the unit 100 under test, and the reference voltage Vref is a voltage value related to the resistance reference value RT. By comparing the two, the resistance range of the unit 100 under test can be obtained after conversion. The obtained resistance value should be greater than the minimum resistance value Rmin and less than the maximum resistance value Rmax, i.e. within this range; if not, the test current is not suitable and needs to be reset.

[0035] In another embodiment, the test voltage V1 is the reference value, and the reference voltage Vref is the value to be compared, i.e., the test voltage V1 is a fixed value, for example, the test current providing unit 210 applies a set current reference value I1n to the resistance of the unit under test 100, and obtains a fixed test voltage V1n as the reference value. The reference voltage providing circuit obtains the lower limit value and the upper limit value of the reference voltage according to the preset minimum resistance value Rmin and the maximum resistance value Rmax, respectively, and takes the lower limit value and the upper limit value of the reference voltage as the first boundary value and the second boundary value, respectively. Through comparison of the two, the resistance range of the unit under test 100 can be obtained after conversion. The obtained resistance value should be within the range formed by the minimum resistance value Rmin and the maximum resistance value Rmax, if not, the reference voltage Vref is not appropriate, and the value to be compared needs to be reset.

[0036] Further, after determining the upper and lower limits of the value to be compared, the range of values between the two values to be compared can be continuously narrowed through step-by-step adjustment, so as to continuously obtain a resistance range with higher accuracy. That is, the resistance control unit 240 also adjusts the first boundary value and the second boundary value according to the first comparison result, the second comparison result and the detection accuracy, so as to update the detected resistance range until the resistance range reaches the detection accuracy. In each step-by-step adjustment, the interval value range bounded by the first boundary value and the second boundary value is reduced, so that the measured resistance value continuously approaches the true resistance value. For the two examples provided above, the resistance control unit 240 adjusts the test current generated by the test current providing unit 210 to adjust the first boundary value and the second boundary value, or adjusts the voltage value generated by the reference voltage providing circuit to adjust the first boundary value and the second boundary value. The comparison unit 230 compares and outputs the comparison result multiple times, and the resistance control unit 240 obtains the resistance range multiple times, so as to continuously improve the accuracy of the detected resistance and the accuracy of the resistance detection.

[0037] Figure 3 A schematic flowchart of a resistance detection method according to an embodiment of the present application is shown. As shown in FIG. 1, the resistance detection method includes steps S101-S104, which are as follows: Figure 3

[0038] In step S101, the test voltage and the reference voltage are obtained, one of which is set as the value to be compared, and the other is set as the reference value with a fixed value. The value to be compared includes the first boundary value and the second boundary value. In this step, the test voltage V1 is the voltage value obtained by applying the test current to the unit under test 100, and the reference voltage Vref is the voltage value generated by the reference voltage providing circuit.

[0039] ​Specifically, when the test voltage V1 is the value to be compared and the reference voltage Vref is the reference value, the step includes: setting the minimum resistance value Rmin and the maximum resistance value Rmax, and obtaining the upper limit value and the lower limit value of the test current according to the minimum resistance value and the maximum resistance value respectively; applying the upper limit value and the lower limit value of the test current to the resistance of the unit 100 to be tested respectively to obtain the first boundary value V1up and the second boundary value V1dn respectively; setting the resistance reference value RT, and obtaining the reference voltage Vref with a fixed value as the reference value according to the resistance reference value. When the test voltage V1 is the reference value and the reference voltage Vref is the value to be compared, the step includes: setting the minimum resistance value Rmin and the maximum resistance value Rmax, and obtaining the lower limit value and the upper limit value of the reference voltage according to the minimum resistance value and the maximum resistance value respectively, and taking the lower limit value Vref1 and the upper limit value Vref2 of the reference voltage as the first boundary value and the second boundary value respectively; applying the set current reference value I1n to the resistance of the unit 100 to be tested to obtain the test voltage V1n with a fixed value as the reference value.

[0040] In step S102, the first boundary value and the second boundary value are compared with the reference value respectively to obtain the first comparison result and the second comparison result.

[0041] In step S103, the resistance range to which the resistance of the unit to be tested belongs is calculated according to the first comparison result and the second comparison result. The first comparison result and the second comparison result are both inequalities about the resistance R of the unit 100 to be tested, so that the value range of R can be obtained according to the inequalities. If the resistance range calculated according to the first comparison result and the second comparison result does not belong to the resistance interval (Rmin, Rmax) formed by the minimum resistance value and the maximum resistance value, the value to be compared needs to be reset. When the test unit 100 is a PD device, it is considered that the resistance measured at this time does not meet the protocol standard.

[0042] In step S104, the first boundary value and the second boundary value are adjusted according to the first comparison result, the second comparison result and the detection accuracy. After this step, step S102 is executed again, and the cycle is repeated until the appropriate resistance range is detected. That is, the first boundary value and the second boundary value are adjusted step by step according to the first comparison result, the second comparison result and the detection accuracy, so as to update the resistance range until the resistance range reaches the detection accuracy. Each time the first boundary value and the second boundary value are adjusted step by step, the value range of the interval bounded by the first boundary value and the second boundary value is reduced. That is, the test current applied to the unit 100 to be tested is adjusted to adjust the first boundary value and the second boundary value, or the voltage value generated by the reference voltage providing circuit is adjusted to adjust the first boundary value and the second boundary value.

[0043] Specifically, when the test voltage is the value to be compared and the reference voltage Vref is the reference value, the step includes: if the first comparison result is that the first boundary value is greater than the reference value (V1up>Vref) each time, then stepwise decrease the upper limit value of the test current until the first boundary value is less than the reference value; if the second comparison result is that the second boundary value is less than the reference value (V1dnVref) each time, then stepwise increase the lower limit value of the test current until the second boundary value is greater than the reference value; if the resistance range obtained according to the first comparison result and the second comparison result reaches the detection precision, then stop adjusting the first boundary value and the second boundary value. That is, the stepwise adjustment process can be stopped when the resistance range of the resistor reaches the detection precision, or if the resistance range is always within the precision range, then wait until the comparison conditions mentioned above are met.

[0044] When the test voltage V1 is the reference value and the reference voltage is the value to be compared, the step includes: if the first comparison result is that the first boundary value is less than the reference value (VrefV1) each time, then stepwise increase the lower limit value of the reference voltage until the first boundary value is greater than the reference value; if the second comparison result is that the second boundary value is greater than the reference value (Vref2>V1) each time, then stepwise decrease the upper limit value of the reference voltage until the second boundary value is less than the reference value; if the resistance range obtained according to the first comparison result and the second comparison result reaches the detection precision, then stop adjusting the first boundary value and the second boundary value. The stepwise adjustment process of this example is similar to that of the above embodiment, and will not be described here.

[0045] When the unit to be measured 100 is a powered device, if the resistance range is within the resistance range specified by the protocol, it is determined that the impedance of the powered device meets the protocol standard. If the resistance range does not completely fall within the resistance range specified by the protocol, it is considered that the impedance of the powered device does not meet the protocol standard. Here, the determination that the resistance range falls within the resistance range specified by the protocol means that the measured resistance range completely falls within the resistance range specified by the protocol.

[0046] The following describes the case where the test voltage is the value to be compared and the reference voltage is the value to be compared in combination with the circuit diagram example of Figures 4-5 .

[0047] Figure 4The schematic circuit diagram of the resistance detection circuit according to the first embodiment of the present application is shown. Here, the unit 100 to be detected is taken as an example of a PD device, i.e. the impedance of a powered device at a PD powered port is detected. The powered device is simplified as a circuit formed by two diodes and a resistor in series, and the characteristic resistance is R, so the voltage difference across the powered port is V1=VD+I1×R, and VD is the voltage drop across the two diodes. The test current providing unit 210 can include a current source, and the comparison unit 230 can include one or two comparators, e.g. only a comparator U1, or both the comparator U1 and the comparator U2. Here, the comparison unit 230 is taken as an example of including only one comparator U1, and in this case the comparator U1 is time-multiplexed in judging the resistance range each time. Since the characteristic resistance limit specified by the POE protocol is a resistance range, the present embodiment can correspondingly detect a resistance range Rx1-Rx2. That is, different voltage drops V1 are generated by applying different currents I1 at the PD powered port, to be compared with the reference voltage Vref, and the resistance range can be judged by the output of the comparison unit.

[0048] As shown in Figure 4 , the fixed reference voltage can be set as Vref=VD+I0×RT, where I0 is a fixed test current value, but the value needs to ensure that the Vref voltage is less than the upper limit of the detection voltage range (e.g. 0-10V) of the protocol, and preferably can take the middle value of the detection voltage range, e.g. by setting I0 so that Vref=5V. Then, according to the principle of the comparator, when Vref>V1, R<I0×RT / I1, and vice versa, VrefV1, R>I0×RT / I1. When the test voltage at the two boundaries of a large value interval is compared with the reference voltage respectively, R can be controlled to be within a range, i.e. greater than a certain value and less than another value. At this time, the comparator U1 receives the two boundary values in time, and compares them with the same reference value. The two comparison results of the comparator U1 are input to the resistance control unit 240, and the resistance control unit 240 can obtain a resistance range by algorithm, so as to adjust the current change of the test current providing unit 210.

[0049] In this embodiment, in the first two detections, first set the boundary values of the two test currents, namely I1max=I0xRT / Rmin and I1min=I0xRT / Rmax, so that the corresponding two test voltage values can be obtained, which are V1up and V1dn respectively. In general, V1up>Vref and V1dnVref. V1up and V1dn are input into the comparator U1 in turn and compared with Vref respectively. According to the two comparison results, a resistance range can be obtained. The minimum resistance value Rmin and the maximum resistance value Rmax are the minimum and maximum values of the characteristic impedance expected by the PSE power supply end, which can also be set according to user requirements. I1max is the upper limit of the current, and the corresponding test voltage V1up is the first boundary value. I1min is the lower limit of the current, and the corresponding test voltage V1dn is the second boundary value. Then R should be in the range of (Rmin, Rmax) after calculation. If it is detected according to the results of the comparator that R is less than Rmin or R is greater than Rmax, it is directly determined that the impedance of the powered end does not meet the protocol standard.

[0050] If R is in the range of (Rmin, Rmax), I1max and I1min are adjusted in the subsequent detection according to the current step set by the resistance detection accuracy, so that the value interval between the two is continuously reduced. That is, the step value is set according to the resistance detection accuracy, and then I1max is correspondingly reduced and I1min is correspondingly increased. Then the resistance range is updated according to the comparison results of the detection voltages V1up and V1dn and the reference voltage Vref. When I1max is reduced, if it still meets V1up>Vref, i.e. R>I0xRT / I1max, I1max continues to be reduced next time, and I1max is continuously stepped down until V1upVref, i.e. R<I0xRT / I1max, I1max stops decreasing, and the maximum lower limit value of R can be measured. In addition, similar judgment is also made when I1min is stepped up according to the detection accuracy, i.e. if it still meets V1dnVref, i.e. R<I0xRT / I1min, I1min continues to be increased next time, until V1dn>Vref, i.e. Rd>I0xRT / I1min, I1min stops increasing, and the minimum upper limit value of R is obtained. Finally, when I1max and I1min both stop changing, I0xRT / I1max<R<I0xRT / I1min. That is, the resistance range of R is obtained. If the value of (I0xRT / I1max, I0xRT / I1min) falls completely within the resistance range specified by the protocol, the powered device meets the protocol requirements.

[0051] Figure 5 A schematic circuit diagram of a resistance detection circuit according to the second embodiment of the application is shown.

[0052] Similar to Figure 4 that, the resistance detection circuit 200 includes a test current providing unit 210, a test voltage obtaining unit 220, a comparison unit 230, and a resistance control unit 240. In this embodiment, it is exemplified that the comparison unit 230 includes two comparators, namely comparator U1 and comparator U2. As Figure 5 shown, a fixed voltage drop V1 = VD + I1×R is generated by applying a fixed current I1 to the PD power receiving port, and this is used as the fixed test voltage V1, that is, a fixed reference value. Then, the test voltage V1 is compared with different reference voltages Vref, and the resistance value range of the resistor is judged through the output of the comparator. Similar to Figure 4 the setting, the voltage drop of the two diodes is VD, the characteristic resistance is R, and the resistance reference value is RT, then the reference voltage can be set as: Vref = VD + I1×Rref. When Vref > V1, R < Rref; when Vref < V1, R > Rref. The result of the comparator is input to the resistance control unit 240, and the resistance control unit 240 determines the change of Vref through an algorithm.

[0053] Specifically, in the first two detections, set Vref1 = VD + I1×Rrefmin and Vref2 = VD + I1×Rrefmax to limit R within the range (Rrefmin, Rrefmax). Here, Rrefmin and Rrefmax are the minimum and maximum values of the characteristic impedance desired by the PSE power supply end, which can be equivalent to the aforementioned Rmin and Rmax, that is, two boundary values are obtained according to the minimum and maximum resistance values. In the cases where the measured R is less than Rrefmin and greater than Rrefmax after passing through the comparator, it is directly determined that the power receiving end does not conform to the protocol. And if R is indeed within the range (Rrefmin, Rrefmax), in subsequent detections, adjust Vref1 and Vref2 according to the current step value set according to the resistance detection accuracy, so that the value interval between the two continuously shrinks. That is, set the step value according to the resistance detection accuracy, and then correspondingly decrease Vref2 and increase Vref1. Then continue to update the resistance value range according to the comparison results of the detection voltage V1 with Vref1 and Vref2 respectively. Since Vref1 = VD + I1×Rrefmin, Vref2 = VD + I1×Rrefmax, and VD and I1 are both fixed values, so here it is actually step - adjusting the sizes of Rrefmin and Rrefmax to step - adjust Vref1 and Vref2. Moreover, in this embodiment, the reference voltage generation circuit can be arranged inside the resistance control unit 240, which is more convenient for controlling the reference voltage.

[0054] In the adjustment process, when Vref1 increases, if Vref1V1, i.e. R>Rref1, then the next time Vref1 continues to increase until Vref1>V1, i.e. R<Rref1, then Vref1 stops increasing. Similarly, when Vref2 decreases, if Vref2>V1, i.e. R<Rref2, then the next time Vref2 continues to decrease until Vref2V1, i.e. R>Rref2, then Vref2 stops increasing, and finally when Vref1 and Vref2 both stop changing, then Rref2<R<Rref1. If (Rref2, Rref1) is in the resistance range specified by the protocol, then the powered device meets the protocol requirements. Thus, the resistance of the test unit 100 is detected, which can be accurate to a very small range. The circuit structure is simple, the calculation accuracy is high, the circuit occupies a small area, and the cost is low.

[0055] It should be noted that the values herein are only used for illustrative description, and in other embodiments of the application, other values can also be used to implement the scheme, and the specific values should be reasonably set according to the actual situation, and the application does not limit this.

[0056] Finally, it should be noted that: obviously, the above embodiments are only examples for clearly illustrating the application, and are not limited to the implementation. For those skilled in the art, on the basis of the above description, other different forms of changes or changes can also be made. Here, it is not necessary and impossible to exhaust all the implementation. The obvious changes or changes derived from it are still within the protection scope of the application.

[0057] It should also be understood that the terms and expressions used herein are only used for description, and one or more embodiments of the present application should not be limited to these terms and expressions. The use of these terms and expressions does not mean the exclusion of any equivalent features, and it should be recognized that various modifications that can exist should also be included in the scope of the claims. Other modifications, changes and replacements can also exist. Accordingly, the claims should be considered to cover all these equivalents.

Claims

1. A resistance detection method for detecting the resistance value of a unit under test, wherein, The resistance detection method includes: Obtain the test voltage and the reference voltage, set one of them as the value to be compared, and set the other as a reference value with a fixed value. The value to be compared includes a first boundary value and a second boundary value. The first boundary value and the second boundary value are compared with the reference value respectively to obtain a first comparison result and a second comparison result; The resistance range to which the resistance value of the tested unit belongs is calculated based on the first comparison result and the second comparison result. The test voltage is the voltage value obtained by applying a test current to the unit under test, and the reference voltage is the voltage value generated by the reference voltage providing circuit.

2. The resistance detection method according to claim 1, wherein, The test voltage is the value to be compared, and the reference voltage is the reference value. Obtaining the test voltage and the reference voltage includes: Set a minimum resistance value and a maximum resistance value, and obtain an upper limit value and a lower limit value for the test current based on the minimum resistance value and the maximum resistance value, respectively; The upper limit of the test current and the lower limit of the test current are applied to the resistance of the unit under test, respectively, to obtain the first boundary value and the second boundary value. Set a resistance reference value, and obtain a reference voltage with a fixed value based on the resistance reference value as the reference value.

3. The resistance detection method according to claim 1, wherein, The test voltage is the reference value, and the reference voltage is the value to be compared. Obtaining the test voltage and the reference voltage includes: Set a minimum resistance value and a maximum resistance value, and obtain a lower limit value and a higher limit value of the reference voltage based on the minimum resistance value and the maximum resistance value, respectively. Use the lower limit value and the higher limit value of the reference voltage as the first boundary value and the second boundary value, respectively. A set current reference value is applied to the resistance of the unit under test, and the test voltage with a fixed value is obtained as the reference value.

4. The resistance detection method according to claim 2 or 3, wherein, If the resistance range calculated based on the first comparison result and the second comparison result does not fall within the resistance range formed by the minimum resistance value and the maximum resistance value, the comparison value is reset.

5. The resistance detection method according to claim 2 or 3 further includes: Based on the first comparison result, the second comparison result, and the detection accuracy step, the first boundary value and the second boundary value are adjusted to update the resistance range until the resistance range reaches the detection accuracy. Each step adjustment of the first boundary value and the second boundary value will reduce the range of values ​​in the interval bounded by the first boundary value and the second boundary value.

6. The resistance detection method according to claim 5, wherein, Adjusting the first boundary value and the second boundary value includes: adjusting the test current applied to the unit under test to adjust the first boundary value and the second boundary value, or adjusting the voltage value generated by the reference voltage providing circuit to adjust the first boundary value and the second boundary value.

7. The resistance detection method according to claim 5, wherein, The test voltage is the value to be compared, and the reference voltage is the reference value. The first boundary value and the second boundary value are adjusted stepwise according to the first comparison result, the second comparison result, and the detection accuracy to update the resistance range until the resistance range reaches the detection accuracy, including: If the first comparison result is that the first boundary value is greater than the reference value each time, the upper limit of the test current is gradually reduced until the first boundary value is less than the reference value. If the second comparison result is that the second boundary value is less than the reference value each time, the lower limit of the test current is increased step by step until the second boundary value is greater than the reference value. If the resistance range obtained based on the first comparison result and the second comparison result reaches the detection accuracy, then stop adjusting the first boundary value and the second boundary value.

8. The resistance detection method according to claim 5, wherein, The test voltage is the reference value, the reference voltage is the value to be compared, and the first boundary value and the second boundary value are adjusted stepwise according to the first comparison result, the second comparison result, and the detection accuracy to update the resistance range until the resistance range reaches the detection accuracy, including: If the first comparison result is that the first boundary value is less than the reference value each time, the lower limit of the reference voltage is increased step by step until the first boundary value is greater than the reference value. If the second comparison result is that the second boundary value is greater than the reference value each time, the upper limit of the reference voltage is decreased step by step until the second boundary value is less than the reference value. If the resistance range obtained based on the first comparison result and the second comparison result reaches the detection accuracy, then stop adjusting the first boundary value and the second boundary value.

9. The resistance detection method according to any one of claims 1-3, wherein, The unit under test is a power receiving device. If the resistance value is within the range specified in the protocol, then the impedance of the power receiving device is determined to meet the protocol standard.

10. A resistance detection circuit, connected to a unit under test, for detecting the resistance value of the unit under test, wherein, The resistance detection circuit includes: A test current supply unit applies a test current to the unit under test to generate a test voltage; A test voltage acquisition unit acquires the test voltage from both ends of the unit under test; The comparison unit acquires a reference voltage generated by a reference voltage supply circuit, uses one of the test voltage and the reference voltage as the value to be compared, and the other as a reference value with a fixed value. The value to be compared includes a first boundary value and a second boundary value. The first boundary value and the second boundary value are compared with the reference value respectively to obtain a first comparison result and a second comparison result; and The resistance control unit calculates the resistance range to which the resistance value of the unit under test belongs based on the first comparison result and the second comparison result.

11. The resistance detection circuit according to claim 10, wherein, The resistance control unit further adjusts the first boundary value and the second boundary value in increments based on the first comparison result, the second comparison result, and the detection accuracy, to update the resistance range until the resistance range reaches the detection accuracy. Each step adjustment of the first boundary value and the second boundary value will reduce the range of values ​​in the interval bounded by the first boundary value and the second boundary value.

12. The resistance detection circuit according to claim 11, wherein, The resistance control unit adjusts the first boundary value and the second boundary value by adjusting the test current generated by the test current providing unit, or by adjusting the voltage value generated by the reference voltage providing circuit.

13. The resistance detection circuit according to claim 10, wherein, The test voltage is the value to be compared, and the reference voltage is the reference value. The test current providing unit obtains the upper limit value and the lower limit value of the test current according to the preset minimum resistance value and the maximum resistance value, respectively, and applies the upper limit value and the lower limit value of the test current to the resistance of the unit under test, so as to obtain the first boundary value and the second boundary value accordingly. The reference voltage providing circuit obtains a fixed reference voltage based on a preset resistance reference value, which is then used as the reference value.

14. The resistance detection circuit according to claim 10, wherein, The test voltage is the reference value, and the reference voltage is the value to be compared. The reference voltage providing circuit obtains the lower limit value and the upper limit value of the reference voltage according to the preset minimum resistance value and the maximum resistance value, respectively, and uses the lower limit value and the upper limit value of the reference voltage as the first boundary value and the second boundary value, respectively. The test current providing unit applies a set current reference value to the resistance of the unit under test, and obtains a fixed test voltage as the reference value.

15. The resistance detection circuit according to claim 10, wherein, The comparison unit includes at least one comparator. When the comparison unit includes only one comparator, the comparator receives the first boundary value and the second boundary value in a time-division manner.

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