An ATE device source board channel parallel test system

Abstract

The application provides an ATE device source board channel parallel test system, which comprises a load unit, a VI source board and a plurality of measured load channels, the VI source board is connected with the plurality of measured load channels through signal ports, the load unit selects single-channel independent load or multi-channel parallel load according to a control signal, switches load resistance value according to the control signal, and outputs a load end current signal, a plurality of current-voltage conversion units, input ends of the plurality of current-voltage conversion units are connected with the plurality of measured load channels respectively, and the plurality of current-voltage conversion units are used for converting the load end current signal into a load end voltage signal, a multi-channel voltage measurement unit, the multi-channel voltage measurement unit selects one or more voltage signals according to a control signal, and outputs after conditioning the single-channel signal or performing summation operation on the multi-channel signal, and a control unit, the control unit outputs the control signal and receives measurement data from the multi-channel voltage measurement unit, and the control signal is used for controlling channel selection, load switching and measurement path selection.

Description

Technical Field

[0001] This invention relates to the field of automated test equipment for integrated circuits, and more particularly to a parallel test system for source board channels of ATE equipment. Background Technology

[0002] In ATE testing systems, the VI source board is used to provide power to the chip under test. As chip integration increases, the demand for power supply current continues to grow. Existing ATE testers utilize multi-channel parallel technology to increase output current, with single-channel current reaching over 2A, supporting over 100 channels in parallel, and a total current exceeding 200A. However, load testing of the VI source board faces the following challenges: First, there is a lack of electronic loads on the market that simultaneously support single-channel and multi-channel parallel operation with currents reaching hundreds of amperes, or they are extremely expensive; second, while multimeters offer high measurement accuracy, their current measurement range is limited (maximum approximately 10A), significantly falling short of the 200A+ testing requirements; third, under high current conditions, the voltage drop across the trace resistance between the test point and the load can introduce millivolt-level errors, exceeding the accuracy requirements of the VI board. Therefore, achieving high-precision, low-cost load testing of the VI source board with high current is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of expensive testing equipment, insufficient current measurement range, and large voltage measurement error in the high current load testing of VI source boards in the prior art.

[0004] This invention provides a parallel testing system for source board channels of ATE equipment, comprising:

[0005] The load unit includes a VI source board, a switch matrix, and multiple test load channels. The VI source board is connected to the multiple test load channels through the switch matrix. The load unit selects a single-channel independent load or a multi-channel parallel load according to a control signal, and switches the load resistance value according to the control signal.

[0006] Multiple current-to-voltage conversion units are connected to the multiple measured load channels respectively, and are used to convert the load current of each measured load channel into a corresponding converted voltage signal;

[0007] A multi-channel voltage measurement unit is used to receive multiple converted voltage signals and output a total converted voltage signal;

[0008] An external measurement unit, connected to the switch matrix and the multi-channel voltage measurement unit, is used to measure load current and load voltage, or to measure the total conversion voltage signal;

[0009] The control unit outputs the control signal, which is used to control channel selection, load switching, and measurement path selection.

[0010] Furthermore, each of the tested load channels includes an input terminal, a first output terminal, and a second output terminal;

[0011] The input terminal of the load under test channel is connected to the FRC port of the VI source board;

[0012] The first output terminal of the load under test channel is connected to the current-voltage conversion unit via a switching relay.

[0013] The second output terminal of the load under test channel is connected to the positive terminal of an external measurement unit via a measurement relay switch.

[0014] Furthermore, each of the tested load channels also includes a parallel relay switch and a conductive connector;

[0015] The input terminal is connected to the conductive connector via the parallel relay switch;

[0016] The single-channel independent load or multi-channel parallel load can be switched by controlling the closed state of the parallel relay switch.

[0017] Furthermore, each of the tested load channels includes a load network, the load network including multiple load resistors connected in parallel, and each load resistor connected in series with a load relay switch.

[0018] Furthermore, the multiple load resistors have different resistance values, and the load resistance value can be adjusted in multiple levels by controlling the closing combination of each load relay switch; when multiple load relay switches are closed at the same time, the load resistance value is the parallel value of the corresponding multiple load resistors.

[0019] Furthermore, the current-to-voltage conversion unit includes a first amplifier, the non-inverting input terminal of the first amplifier is connected to one end of an input resistor, the other end of the input resistor is connected to the load unit and one end of a sampling resistor, and the other end of the sampling resistor is grounded.

[0020] The inverting input terminal of the first amplifier is connected to one end of a grounding resistor and one end of a feedback resistor, respectively. The other end of the grounding resistor is grounded, and the other end of the feedback resistor is connected to the output terminal of the first amplifier.

[0021] Furthermore, the multi-channel voltage measurement unit includes multiple input terminals, which are respectively connected to the output terminals of multiple current-voltage conversion units.

[0022] Furthermore, each of the input terminals is connected in series with a first fixed resistor and then in parallel to one end of a second fixed resistor and the inverting input terminal of a second amplifier. The non-inverting input terminal of the second amplifier is grounded, and the output terminal of the second amplifier is connected to the other end of the second fixed resistor and then to the positive terminal of an external measurement unit.

[0023] Furthermore, when the load unit is a single-channel independent load, the external measurement unit directly measures the load current and load voltage;

[0024] When the load unit is a multi-channel parallel load, the external measurement unit measures the total conversion voltage signal.

[0025] Furthermore, when the load unit is a multi-channel parallel load, the total load current is

[0026]

[0027] Where Vm is the total conversion voltage signal, R3 is the first fixed resistor, R4 is the second fixed resistor, Rg is the input resistor, Rf is the feedback resistor, and Rsen is the sampling resistor.

[0028] Compared with existing technologies, the present invention has at least the following advantages: it breaks through the current output capability limitation of a single VI source board channel by using a multi-channel parallel connection method, realizing high-current load testing; it improves the system's flexibility and versatility through a switchable load resistance design; it simplifies the current measurement process when multiple channels are connected in parallel by using the summation function of the multi-channel voltage measurement unit; and it achieves coordinated control of channel selection, load switching, and measurement path through a unified control unit, reducing operational complexity and improving testing efficiency and reliability. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0030] Figure 1 This is an overall schematic diagram of the parallel testing system for the source board channels of an ATE device according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of a load unit in one embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of a current-to-voltage conversion unit in one embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram of a multi-channel voltage measurement unit in one embodiment of the present invention;

[0034] Figure 5 This is a schematic diagram of the connection between the VI source board and multiple test load channels in one embodiment of the present invention;

[0035] Figure 6 This is a single-channel block diagram of the VI source board in one embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram of a single-channel detection process in one embodiment of the present invention;

[0037] Figure 8 This is a schematic diagram of the multi-channel detection process in another embodiment of the present invention.

[0038] Wherein, R1 - first load resistor; R2 - second load resistor; R3 - first fixed resistor; R4 - second fixed resistor; Rf - feedback resistor; Rin - connection input resistor; Rsen - sampling resistor; Rg - grounding resistor; K1 - first load relay switch; K2 - second load relay switch; K3 - parallel relay switch; K4 - changeover relay switch; K5 - measurement relay switch; K_V - first relay switch; K_I - second relay switch; A1 - first operational amplifier; A2 - second operational amplifier; A3 - third operational amplifier. Detailed Implementation

[0039] The present invention will now be described in more detail with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being broadly known to those skilled in the art and is not intended to limit the invention.

[0040] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0041] The invention is described more specifically by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0042] This invention provides a parallel testing system for source board channels of ATE equipment. Please refer to [link / reference]. Figures 1-6 ,include:

[0043] The load unit includes a VI source board, a switch matrix, and multiple test load channels. The VI source board is connected to the multiple test load channels through the switch matrix. The load unit selects a single-channel independent load or a multi-channel parallel load according to a control signal, and switches the load resistance value according to the control signal.

[0044] Multiple current-to-voltage conversion units are connected to the multiple measured load channels respectively, and are used to convert the load current of each measured load channel into a corresponding converted voltage signal.

[0045] The multi-channel voltage measurement unit is used to receive multiple converted voltage signals and output a total converted voltage signal.

[0046] An external measurement unit, connected to the switch matrix and the multi-channel voltage measurement unit, is used to measure load current and load voltage, or to measure the total conversion voltage signal.

[0047] The control unit outputs the control signal, which is used to control channel selection, load switching, and measurement path selection.

[0048] Specifically, the control unit can flexibly select between two operating modes—single-channel independent testing or multi-channel parallel testing—based on control signals, and can dynamically switch the load resistance value. The system consists of a VI source board connected to multiple test load channels via a switch matrix. The load current of each channel is converted into a voltage signal by a dedicated current-to-voltage conversion unit.

[0049] In single-channel independent testing mode, the external measurement unit directly measures the load current and voltage of a single channel. In multi-channel parallel testing mode, multiple voltage measurement units combine the converted voltage signals from each channel into a single total converted voltage signal, which is then measured by the external measurement unit to indirectly obtain the total current of all parallel channels. This approach ensures both accurate single-channel testing capabilities and efficient testing under multi-channel parallel conditions, effectively solving the measurement challenges of traditional ATE equipment during parallel testing.

[0050] Furthermore, each of the tested load channels includes an input terminal, a first output terminal, and a second output terminal.

[0051] The input terminal of the load under test channel is connected to the FRC port of the VI source board (i.e., connected to the output terminal of the VI source board).

[0052] The first output terminal of the load under test channel is connected to the current-voltage conversion unit via a switching relay K4.

[0053] The second output terminal of the load under test channel is connected to the positive terminal of the external measurement unit through the measurement relay switch K5.

[0054] Please refer to Figure 1 and Figure 5 The VI source board includes multiple FRC ports (output terminals), multiple SEN ports (detection terminals), and multiple DGS ports (ground detection terminals). When the load unit is a multi-channel parallel load, the input terminals of the measured load channels are connected one-to-one with the FRC ports. Specifically, the FRC ports, as key signal ports of the VI source board, are used to provide excitation signals to the measured load channels. The switching relay K4, implemented using an electromagnetic relay or a solid-state relay, is used to switch the connection state between the measured load channel and the current-to-voltage conversion unit. The external measurement unit is a high-precision multimeter or data acquisition card, whose positive input terminal is connected to the measurement relay switch K5 via a low-resistance path.

[0055] Through a split output design, the first output terminal implements current-to-voltage conversion, while the second output terminal retains the original current measurement path. The coordinated operation of the switching relay K4 and the measuring relay K5 allows the system to perform both indirect high-current measurement via the current-to-voltage conversion unit and high-precision direct measurement via an external measuring unit. For example, during single-channel testing, the measuring relay K5 can be closed to directly acquire the current signal; during multi-channel parallel testing, the switching relay K4 converts the current signal into a voltage signal for measurement. This dual-path design effectively solves the problem of insufficient current measurement range in traditional multimeters, while avoiding systematic errors caused by a single measurement method.

[0056] Furthermore, each of the tested load channels also includes a parallel relay switch K3 and a conductive connector.

[0057] The input terminal is connected to the conductive connector via the parallel relay switch K3.

[0058] The single-channel independent load or multi-channel parallel load can be switched by controlling the closed state of the parallel relay switch K3.

[0059] Specifically, each test load channel is equipped with a parallel relay switch K3 and a conductive connector to physically switch between single-channel and multi-channel modes. Specifically, the input terminals of each channel are connected to a common conductive connector via the parallel relay switch K3. When a single-channel independent test is required, only the parallel relay switch K3 of one channel is closed, and that channel receives the signal from the VI source board independently. When a multi-channel parallel test is required, the parallel relay switches K3 of multiple channels are closed simultaneously. These channels are then electrically connected in parallel via the conductive connector and connected to the same output port of the VI source board, thus enabling parallel operation of multi-channel loads. This relay switch control method is simple and reliable, and channel combinations can be flexibly configured according to test requirements.

[0060] Furthermore, each of the tested load channels includes a load network, the load network including multiple load resistors connected in parallel, and each load resistor connected in series with a load relay switch.

[0061] Furthermore, the multiple load resistors have different resistance values, and the load resistance value can be adjusted in multiple levels by controlling the closing combination of each load relay switch; when multiple load relay switches are closed at the same time, the load resistance value is the parallel value of the corresponding multiple load resistors.

[0062] Specifically, the load resistor values ​​can be configured in a geometric or arithmetic sequence, such as a combination of 1Ω, 2Ω, 4Ω, and 8Ω. Please refer to [reference needed]. Figure 2 , Figure 2 Only two load resistors are shown: the first load resistor R1 and the second load resistor R2. The first load resistor R1 is connected in series with the first load relay switch K1, and the second load resistor R2 is connected in series with the second load relay switch K2. The relay switches can be electromagnetic relays or solid-state relays, and their control signals are issued by the control unit. By combining and closing different relay switches, multi-level adjustment from the minimum to the maximum resistance value can be achieved. For example, when a smaller resistance value is needed, the switch corresponding to the smaller resistance value can be closed; when a larger resistance value is needed, the switch corresponding to the larger resistance value can be closed. If an intermediate resistance value is required, it can be achieved by connecting multiple resistors in parallel.

[0063] By combining a parallel resistor network and a relay switch, flexible adjustment of the load resistance is achieved. Compared to fixed-resistance loads, it better adapts to the needs of different testing scenarios. Especially under high-current testing conditions, by precisely controlling the number and value combination of parallel resistors, the total load resistance can be effectively controlled, ensuring accurate current measurement. Simultaneously, the use of a relay switch for resistance switching provides a fast response time, which helps improve testing efficiency.

[0064] Furthermore, the current-to-voltage conversion unit includes a first amplifier, the non-inverting input terminal of the first amplifier is connected to one end of the input resistor Rin, the other end of the input resistor is connected to the load unit and one end of the sampling resistor Rsen, and the other end of the sampling resistor Rsen is grounded.

[0065] The inverting input terminal of the first amplifier is connected to one end of the grounding resistor Rg and the feedback resistor Rf, respectively. The other end of the grounding resistor Rg is grounded, and the other end of the feedback resistor Rf is connected to the output terminal of the first amplifier.

[0066] Specifically, the first amplifier uses an operational amplifier to implement current-to-voltage conversion. The input resistor receives the current signal from the load unit, and the sampling resistor Rsen converts the current signal into a voltage signal. The feedback resistor Rf and the grounding resistor Rg form a negative feedback network to stabilize the amplifier's gain. In a preferred embodiment, a precision operational amplifier can be used as the first amplifier, with a low-temperature drift metal film resistor as the input resistor and a high-power manganese copper resistor as the sampling resistor Rsen to withstand large currents. The ratio of the feedback resistor Rf to the grounding resistor Rg determines the amplification factor; a typical configuration is a 1:100 ratio to achieve millivolt-level voltage output.

[0067] An operational amplifier, in conjunction with a precision resistor network, converts a high-current load signal into a low-voltage signal for measurement. The sampling resistor Rsen is directly connected in series in the load circuit, avoiding measurement errors introduced by trace resistance. The feedback network employs a differential input structure, effectively suppressing common-mode interference. Compared to traditional shunt measurement methods, while maintaining the milliohm-level sampling resistor Rsen, the signal amplitude is increased through amplifier gain, thus balancing the requirements of high current carrying capacity and high-precision measurement.

[0068] Furthermore, the multi-channel voltage measurement unit includes multiple input terminals, which are respectively connected to the output terminals of multiple current-voltage conversion units.

[0069] Furthermore, each of the input terminals is connected in series with the first fixed resistor R3 and then in parallel to one end of the second fixed resistor R4 and the inverting input terminal of the second amplifier. The non-inverting input terminal of the second amplifier is grounded, and the output terminal of the second amplifier is connected to the other end of the second fixed resistor R4 and then to the positive terminal of the external measurement unit.

[0070] Specifically, each input terminal is directly connected to the output terminal of the corresponding current-to-voltage conversion unit through an independent signal path, forming a one-to-one mapping relationship. The first fixed resistor R3 is used to limit the input current and achieve signal attenuation; its resistance value can be selected from 1kΩ to 10kΩ depending on the actual measurement range. The second fixed resistor R4 and the second amplifier constitute an inverting proportional amplifier circuit, and the amplification factor is determined by the ratio of the second fixed resistor R4 to the first fixed resistor R3. The second amplifier is preferably a low-noise precision operational amplifier with an input bias current of less than 1nA. As a preferred embodiment, a compensation capacitor can be added between the inverting input terminal of the second amplifier and ground to suppress high-frequency noise. In another embodiment, the second fixed resistor R4 can be a programmable digital potentiometer, with the amplification factor dynamically adjusted by a control unit.

[0071] This system achieves parallel processing of multiple voltage signals by combining a fixed resistor network with an inverting amplifier. The series design of the first fixed resistor R3 effectively isolates mutual interference between the input channels, while the feedback structure of the second amplifier ensures the linearity of signal superposition. Compared to traditional multiplexer solutions, this avoids measurement errors introduced by the switch's on-resistance.

[0072] Please refer to Figure 6 The core of the VI source board's single-channel design consists of three operational amplifiers: operational amplifier A1, operational amplifier A2, and operational amplifier A3. FV / FI is a mode selection signal used to control the operating mode of the source board: FV (Force Voltage) - Forced voltage mode / voltage source mode; FI (Force Current) - Forced current mode / current source mode. When the first relay switch K_V is closed and the second relay switch K_I is open, operational amplifier A1 operates in constant voltage source mode, outputting voltage to the load through its output terminal. When the first relay switch K_V is open and the second relay switch K_I is closed, operational amplifier A1 operates in constant current source mode, outputting current to the load through its output terminal. The channel ADC resource can measure channel current (Measure I) or channel voltage (Measure V). According to the VI source board's single-channel block diagram, the VI source board achieves regulated output and voltage measurement through the SEN port (sensor terminal) and the DGS port (ground sensor terminal). When evaluating the accuracy of the source board output voltage or voltage test accuracy, the multimeter test points should be consistent with the SEN and DGS ports.

[0073] Furthermore, when the load unit is a single-channel independent load, the external measurement unit directly measures the load current and load voltage.

[0074] When the load unit is a multi-channel parallel load, the external measurement unit measures the total conversion voltage signal.

[0075] The system employs different measurement strategies based on the operating mode to ensure measurement accuracy. Please refer to [reference needed]. Figures 7-8In single-channel independent load mode, the external measurement unit is directly connected to the channel under test via a switch matrix to measure the load current and load voltage of that channel in real time, obtaining the precise electrical parameters of that channel. However, in multi-channel parallel load mode, because multiple channels operate in parallel, a single measurement point cannot accurately reflect the current distribution of each channel. Therefore, the system adopts an indirect measurement method: the load current of each channel is first converted into a voltage signal by its respective current-to-voltage conversion unit. Then, these voltage signals are aggregated into a total converted voltage signal by a multi-channel voltage measurement unit. After the external measurement unit measures this total signal, it can calculate the total load current of all parallel channels using the known conversion relationship. This adaptive measurement path switching mechanism not only makes single-channel testing direct and accurate but also solves the problem of measuring the total current when multiple channels are connected in parallel.

[0076] Furthermore, when the load unit is a multi-channel parallel load, the total load current is:

[0077]

[0078] Where Vm is the total conversion voltage signal, R3 is the first fixed resistor, R4 is the second fixed resistor, Rg is the input resistor, Rf is the feedback resistor, and Rsen is the sampling resistor.

[0079] In multi-channel parallel load mode, the control unit converts the total converted voltage signal measured by the external measuring unit into the actual total load current through a specific mathematical model. By comprehensively considering the influence of all key resistor parameters in the current-to-voltage conversion circuit and the multi-channel voltage summarization circuit, a precise relationship between the total converted voltage signal and the total load current is established. In this way, the system can accurately deduce the total current value of multiple parallel channels from the indirectly measured voltage signal, achieving high-precision parallel load current testing and avoiding measurement errors and circuit interference that may be introduced by directly connecting the ammeter in series in traditional methods.

[0080] The above examples illustrate the present invention only to aid in understanding it and are not intended to limit the scope of the invention. Those skilled in the art can make various simple deductions, modifications, or substitutions based on the principles of this invention.

Claims

1. A parallel testing system for source board channels of ATE equipment, characterized in that, include: The load unit includes a VI source board, a switch matrix, and multiple test load channels. The VI source board is connected to the multiple test load channels through the switch matrix. The load unit selects a single-channel independent load or a multi-channel parallel load according to a control signal, and switches the load resistance value according to the control signal. Multiple current-to-voltage conversion units are connected to the multiple measured load channels respectively, and are used to convert the load current of each measured load channel into a corresponding converted voltage signal; A multi-channel voltage measurement unit is used to receive multiple converted voltage signals and output a total converted voltage signal; An external measurement unit, connected to the switch matrix and the multi-channel voltage measurement unit, is used to measure load current and load voltage, or to measure the total conversion voltage signal; The control unit outputs the control signal, which is used to control channel selection, load switching, and measurement path selection. The current-to-voltage conversion unit includes a first amplifier, the non-inverting input terminal of the first amplifier is connected to one end of an input resistor, the other end of the input resistor is connected to the load unit and one end of a sampling resistor, and the other end of the sampling resistor is grounded. The inverting input terminal of the first amplifier is connected to one end of a grounding resistor and one end of a feedback resistor, respectively. The other end of the grounding resistor is grounded, and the other end of the feedback resistor is connected to the output terminal of the first amplifier. The multi-channel voltage measurement unit includes multiple input terminals, which are respectively connected to the output terminals of multiple current-voltage conversion units; Each of the input terminals is connected in series with a first fixed resistor and then in parallel to one end of a second fixed resistor and the inverting input terminal of the second amplifier. The non-inverting input terminal of the second amplifier is grounded, and the output terminal of the second amplifier is connected to the other end of the second fixed resistor and then to the positive terminal of an external measurement unit. When the load unit is a multi-channel parallel load, the external measurement unit measures the total conversion voltage signal; When the load unit is a multi-channel parallel load, the total load current is: Where Vm is the total conversion voltage signal, R3 is the first fixed resistor, R4 is the second fixed resistor, Rg is the input resistor, Rf is the feedback resistor, and Rsen is the sampling resistor.

2. The ATE equipment source board channel parallel testing system as described in claim 1, characterized in that, Each of the tested load channels includes an input terminal, a first output terminal, and a second output terminal; The input terminal of the load under test channel is connected to the FRC port of the VI source board; The first output terminal of the load under test channel is connected to the current-voltage conversion unit via a switching relay. The second output terminal of the load under test channel is connected to an external measurement unit via a measurement relay switch.

3. The ATE equipment source board channel parallel testing system as described in claim 2, characterized in that, Each of the tested load channels also includes a parallel relay switch and a conductive connector; The input terminal is connected to the conductive connector via the parallel relay switch; The single-channel independent load or multi-channel parallel load can be switched by controlling the closed state of the parallel relay switch.

4. The ATE equipment source board channel parallel test system as described in claim 2, characterized in that, Each of the tested load channels includes a load network, the load network including multiple load resistors in parallel, and each load resistor in series with a load relay switch.

5. The parallel testing system for ATE equipment source board channels according to claim 4, characterized in that, The multiple parallel load resistors have different resistance values. By controlling the closing combination of each load relay switch, the load resistance value can be adjusted in multiple levels. When multiple load relay switches are closed at the same time, the load resistance value is the parallel value of the corresponding multiple load resistors.

6. The ATE equipment source board channel parallel testing system as described in claim 1, characterized in that, When the load unit is a single-channel independent load, the external measurement unit directly measures the load current and load voltage.

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