Semiconductor DC parameter test system based on Raspberry Pi

Abstract

The invention belongs to the technical field of semiconductor measurement, and particularly relates to a semiconductor direct current parameter test system based on Raspberry Pi. The test system comprises a Raspberry Pi, a switching power supply module, a floating power supply module, a voltage detection module, a current electrical measurement module, an amplification circuit module, a mode and range selection module, a clamping and integrating circuit module, a push-pull amplification circuit module, a DAC and ADC module and a signal transmission port. All the modules are connected to the PCB; according to the invention, high-precision four-quadrant source measurement and automatic measuring range switching in a wide dynamic range can be realized, and the test efficiency is greatly improved; a multiplex circuit structure is adopted, and single-system voltage measuring current applying and current measuring voltage applying are achieved; independent power supply conversion is adopted, and large-range and low-noise driving of room electricity is achieved; the circuit structure is highly integrated and the cost is controllable; according to the invention, the stability and reliability of the system can be improved, the safety of the equipment and the to-be-tested piece is guaranteed, excellent robustness is shown, and the repeatability of a test result is ensured.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor measurement technology, and specifically relates to a semiconductor DC parameter testing system. Background Technology

[0002] The rapid development of semiconductors and integrated circuits across various industries has spurred the booming market for electrical measurement, which aims to accurately characterize their performance. However, due to the highly specialized nature of this field and its relatively specific applications, the current market for mainstream semiconductor parameter measurement instruments is largely monopolized by a few international electronic measurement companies. These devices generally suffer from problems such as high price, large size, and complex use and maintenance.

[0003] As a core device in integrated circuit testing, the source measurement unit (SMU) can provide high-precision programmable four-quadrant voltage and current output, and monitor and calibrate the output signal in real time. It is equipped with a complete overvoltage and overcurrent protection mechanism, which ensures test safety and reliability while having the characteristics of high precision, fast response and high flexibility [1].

[0004] Although domestic companies such as Prosys Instruments and Proton Precision have made some progress, they still face huge challenges in terms of overall technical level and market share. In terms of academic and engineering practice, the University of Electronic Science and Technology of China in Chengdu designed a micro test system based on FPGA, but there are still obvious deficiencies in the dynamic range and accuracy of voltage and current [2]. Jon Munson et al. proposed to use a combination of operational amplifier and complementary transistor to realize a four-quadrant power supply [3]. Jin Furong et al. used a high-power bipolar operational amplifier to realize a regulated four-quadrant voltage source [4]. Shi Yakun et al. expanded the output quadrant through an NPN / PNP three-stage amplification structure [5].

[0005] Therefore, developing a low-cost, compact, and easy-to-use and maintain semiconductor parameter measurement system, while meeting the basic testing requirements of conventional semiconductor devices, is of great significance for improving production efficiency and lowering the application threshold.

[0006] References: [1] A brand-new source measurement unit meets the measurement application requirements of high-power devices [J]. Foreign Electronic Measurement Technology, 2016, 35(01):27. [2] Ning Kang. DC parameter testing of multi-channel high-precision integrated circuits [D]. University of Electronic Science and Technology of China, 2010. [3] Munson J. A four-quadrant power supply that can provide voltage and current of arbitrary polarity[J]. Electronic Design Technology, 2004,(05):109-110. [4] Jin Furong, Li Zhijie, Zheng Tianyun. Design of programmable high-precision four-quadrant power supply [J]. Radio Engineering, 2018, 48(08):714-717. [5] Beijing Dahua Radio Instrument Co., Ltd. High-precision four-quadrant source carrier device: CN202011341307.X[P]. 2021-03-05. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a semiconductor DC parameter measurement system that features high measurement accuracy, fast measurement speed, and low cost, in order to meet the requirements for DC electrical parameter measurement with a large voltage and current dynamic range and integrated voltage and current excitation and measurement.

[0008] The semiconductor DC parameter testing system provided by this invention has the following framework: Figure 1 As shown, it includes: Raspberry Pi 5, switching power supply module, floating ground power supply module, voltage detection module, current measurement module, amplifier circuit module, mode and range selection module, clamping and integrating circuit module, push-pull amplifier circuit module, DAC and ADC modules, signal transmission ports, and a housing; each module is connected to a double-layer PCB board via terminals or pins; among which: The Raspberry Pi 5 serves as the core controller and data processing center. It controls external precision analog circuits (ADC / DAC) through interfaces such as GPIO, SPI, or I²C to complete voltage / current output and measurement. It is also responsible for running test processes, processing data, and providing human-computer interaction and network communication functions, thereby building an open-source intelligent test platform in a low-cost and highly flexible manner. The switching power supply module is used for power conversion, providing stable DC power at ±5V, ±12V, and ±15V, as well as higher voltage AC power for powering various circuits on the circuit board. The switching power supply module adopts a flyback topology, has a complete structure, and features multiple outputs and basic protection functions. It includes input stage circuitry, output stage circuitry, switching circuitry, control and feedback loops, and overcurrent protection circuitry.

[0009] The floating power module is used to provide stable isolated DC power supplies for positive and negative high and low voltages to drive the amplifier circuit module and generate a voltage difference; the circuit includes a high voltage rectifier and filter module and a low voltage capacitor step-down and voltage regulator module.

[0010] The voltage detection module is used to measure the voltage of the device under test or the load, and to proportionally reduce the voltage before feeding it back to the integration circuit module. The current detection module is used to measure the current of the device under test or the load, and converts the voltage measurement of the series resistor into the current magnitude.

[0011] The amplifier circuit module is used to amplify current and voltage, and drive the voltage or current on the device under test or load.

[0012] The mode and range selection module is used to automatically detect currents of different precisions and apply currents of different precisions.

[0013] The clamping and integrating circuit module is used to limit the initial input voltage range, reduce system error, make the system a closed-loop system, protect the circuit, and generate precise control signals in the closed-loop feedback system.

[0014] The push-pull amplifier circuit module is used to amplify the power of the front-end control signal to drive the external load in a high-efficiency, low-distortion manner. As a power output stage, the core function of this module is to provide bidirectional current driving capability, that is, to supply power (sourcing) and sink power to the load.

[0015] The DAC and ADC modules are used to convert the set digital signal into a voltage signal and to acquire an electrical signal and convert it into a digital signal, which is then sent to the host computer. They also control the circuit modes FVMI and FIMV, such as... Figure 2 and Figure 3 As shown.

[0016] The outer shell is used to integrate the above modules in the same area. It adopts a 2mm thick metal frame, which has a good effect on the overall system integrity, noise prevention, and electrostatic shielding.

[0017] The signal transmission port is a coaxial radio frequency port, used for important signal transmission between the module and the system.

[0018] Furthermore: The Raspberry Pi 5, via interfaces such as GPIO, SPI, or I²C, controls external precision analog circuits (ADC / DAC) to complete voltage / current output and measurement. It is also responsible for running test procedures, processing data, and providing human-computer interaction and network communication functions, including a graphical interface, real-time chart generation, and digital filtering. Its core automatic gain control algorithm, such as... Figure 4 As shown, this allows for the construction of an open-source intelligent testing platform in a low-cost and highly flexible manner; The switching power supply module has the following circuit: Figure 5 As shown, where: The input stage circuit primarily functions to perform EMI filtering and rectification on the AC input. The 220VAC input provides overcurrent protection via a fuse. A negative temperature coefficient thermistor RT1 suppresses inrush current during startup, safety capacitors C2 / C11 filter common-mode / differential-mode interference, and a common-mode inductor L1 further suppresses high-frequency noise. The rectifier bridge U1 converts AC to pulsating DC, and the high-voltage electrolytic capacitor E3 serves as the main DC bus capacitor, smoothing the rectified voltage.

[0019] The output stage circuit primarily functions as rectification, filtering, and providing multiple outputs. Schottky diodes are used for secondary rectification, and their low on-state voltage drop reduces losses. Electrolytic capacitors smooth the output voltage, and an LC filter network (such as L2-L5 and a capacitor combination) further suppresses high-frequency ripple. Multiple voltage outputs of ±15V / ±12V / ±5V are provided, with a linear regulator generating ±5V for low-power loads. The 12V and 15V outputs are obtained directly through rectification and filtering of the secondary winding. LED indicators display the power supply status via current-limiting resistors.

[0020] The core components of the switching circuit are a PWM controller, a power switching transistor, and a high-frequency transformer.

[0021] U2 is a current-mode PWM controller that achieves cycle-by-cycle current limiting by detecting the current signal. Its main pin functions are: VCC (Pin 7): Power supply terminal (typical value 12-18V, provided by auxiliary winding).

[0022] OUT (Pin 6): Drive signal output, directly driving the MOSFET or through the drive circuit (as shown in the totem pole).

[0023] RT / CT (Pin 4): External timing resistor R18 and capacitor C17 determine the switching frequency. FB (Pin 2): Feedback input terminal, receives the error voltage signal transmitted by the optocoupler, and adjusts the duty cycle.

[0024] ISENSE (Pin 3): Current sensing terminal, which monitors the main circuit current by sensing the voltage of resistor R28.

[0025] Within each cycle, the MOSFET's on-time is determined by both the current sensing signal (ISENSE) and the feedback signal (FB), providing both fast response and interference immunity. Furthermore, U2 employs a soft-start mechanism, using C13 to gradually change the duty cycle during startup, preventing input inrush current.

[0026] The selection of power switching transistors is based on voltage rating, on-resistance, and package, and heat dissipation requirements must be considered in the design. NPN transistors accelerate the turn-off of MOSFETs and reduce switching losses. Resistors R23 / R25 limit the drive current and prevent overshoot; resistor R26 is a pull-down resistor to ensure reliable MOSFET turn-off.

[0027] Key parameters of the high-frequency transformer (EE28) include turns ratio and core selection. Leakage inductance energy is dissipated through the RCD absorption circuit, thereby suppressing voltage spikes.

[0028] The control and feedback loop uses U4 to set the output voltage Vref via a voltage divider resistor. When the output voltage increases, the cathode current of U4 increases, leading to increased brightness of the LED inside the optocoupler, enhanced conduction on the optocoupler transistor side, a decrease in the voltage at the FB pin of U2, and a reduction in the duty cycle, thus achieving closed-loop regulation. The compensation method employs Type II compensation (proportional-integral compensation). Capacitor C23 provides integral action, reducing high-frequency gain; resistor R29 adjusts the zero-point frequency, improving phase margin; and capacitor C22 suppresses high-frequency noise, collectively ensuring loop stability.

[0029] The overcurrent protection circuit uses a current sensing resistor R28 to detect the main circuit current, and the signal is sent to U2 via the ISEN pin. When the current exceeds the threshold, U2 shuts off the PWM output, achieving cycle-by-cycle current limiting. The auxiliary power supply circuit supplies power to U2 via 15V_AUX, generated by rectification by D4 and filtering by E8 from the auxiliary winding of the transformer.

[0030] After the design is completed, key design checks should be performed, such as: High-frequency loop layout: Check whether the traces of MOSFET (Q2), transformer (TF1) and rectifier diodes (D1 / D2) are short and thick to reduce parasitic inductance and EMI radiation.

[0031] Feedback loop stability: Verify whether the parameters of the compensation network (C22 / C23) match the response speed of U4 and the optocoupler.

[0032] Heat dissipation design: The MOSFET (Q2) and current sensing resistor (R28) need to be fitted with heat sinks to prevent overheating failure.

[0033] Safety and Isolation: Ensure that the spacing between the primary (220VAC) and secondary (low-voltage output) meets Creepage / Clearance requirements (e.g., >4mm).

[0034] The designed circuit schematic has been verified to meet all requirements and specifications.

[0035] The floating power module has the following circuitry: Figure 6 As shown, where: The high-voltage rectifier and filter module performs full-wave rectification of the input AC power through a bridge rectifier circuit composed of four diodes D1 to D4, and uses two series-connected filter capacitors C1 and C2 to smooth the pulsating DC power after rectification, thereby establishing a symmetrical high-voltage positive and negative DC power supply and a common reference ground. Simultaneously; The low-voltage capacitor step-down and voltage-regulating module uses a capacitor step-down circuit consisting of two capacitors C3 and C5 and two resistors R1 and R2 for current limiting and voltage reduction. After processing by two rectifier elements D5 and D6, the voltage is clamped at a preset low voltage by two Zener diodes D7 and D8. Finally, a smooth and stable low-voltage DC power is output through two filter capacitors C4 and C6. In addition, the circuit also includes a working status indicator circuit consisting of two light-emitting diodes D13 and D14 and their current-limiting resistors to visually display the working status of the high-voltage power supply.

[0036] The voltage detection module has the following circuit: Figure 7 The diagram shows a high-precision differential voltage detection and conditioning circuit. Its core function is to measure the voltage across the load and output a precisely scaled and filtered analog voltage signal referenced to ground. Its operating principle is as follows: The input signals RF6 / RF8 are first buffered by U30 and U31 respectively. U31 uses a floating power supply with RF9 as the common ground to accommodate the high common-mode voltage present in the load. Subsequently, these two buffered signals are sent to the core differential amplifier U32. This operational amplifier, through its external precision resistor network, accurately calculates the voltage difference (V_RF6 - V_RF8) and scales it down proportionally. This circuit accurately subtracts the lower-side voltage and reduces the voltage difference between the high and low ends according to the ratio set by the resistor network (determined by R54 / R65 / R64). A proportional selection port allows for the connection of different resistor sizes to obtain different scaling modes. The RF2 output is a low-voltage signal linearly proportional to the original load voltage, used by subsequent ADC sampling or monitoring systems.

[0037] The current detection module has the following circuit: Figure 8As shown, this circuit is a high-precision differential amplifier with integrated active shielding, designed for precise measurement of the voltage across an external sampling resistor, typically used in high-precision current sensing. Its core is a dual op-amp instrumentation amplifier composed of operational amplifiers U21 and U20. This structure receives differential signals from the inputs RF5 and RF10, utilizing its high common-mode rejection ratio to accurately amplify weak voltage differences while filtering out common-mode noise. The circuit's amplification gain is precisely set by three resistors R56, R58, and R59, ultimately outputting a single-ended signal at the RF3 port that is strictly linearly proportional to the input differential voltage. To achieve extreme measurement accuracy, the circuit integrates an active shielded driver composed of U20. This driver accurately reproduces the common-mode potential of the input signal and drives the GUARD output. By aligning the potential of the input lead's shield with that of the core conductor of the signal, it eliminates measurement errors introduced by parasitic capacitance and leakage current, thus ensuring the overall stability and accuracy of the solution.

[0038] The mode and range selection module has the following circuitry: Figure 9 As shown, using a single current sensing resistor is not feasible for accurate current measurement over a wide dynamic range (e.g., from fA to A). This invention employs a multi-range current sensing scheme. Multiple precision shunt resistors with different resistance values ​​are set in the high-side path of the output current. Depending on the magnitude of the current to be measured, a suitable shunt resistor is selected for connection to the circuit via a low-leakage relay or a dedicated analog switch. For example, a milliohm-level resistor is used when measuring large currents, while a kilohm or megahm-level resistor is switched when measuring small currents. The circuit includes a sampling resistor network composed of multiple precision resistors and two four-channel analog switches controlled by external logic signals. The two analog switches work together to connect different voltage sampling point pairs on the sampling resistor network according to different range selection commands. By changing the equivalent resistance value between the sampling point pairs, switching between multiple precision current measurement ranges from microamps (µA) to milliamps (mA) is achieved. Furthermore, the circuit includes a high-current range controlled by a relay, used to bypass the precision resistor network and switch to an independent low-resistance shunt when measuring larger currents.

[0039] The clamping and integrating circuit module has the following circuitry: Figure 10As shown, the circuit receives a setpoint signal from the digital-to-analog converter (DAC) and a feedback signal from the voltage detection module. It also receives a signal from the I / O expansion chip. The system operating mode (FVMI / FIMI) is selected via the switching chip U11, and an error signal is calculated using a differential circuit composed of an operational amplifier and precision resistors. A clamping circuit, consisting of diodes and Zener diodes, limits the error signal or integration result within a preset safe voltage range to prevent system saturation and overshoot. Subsequently, the signal is fed into an integrating circuit, which is essentially an operational amplifier with an integrating capacitor and an input resistor. This circuit utilizes the charging and discharging characteristics of the capacitor to integrate the error signal, eliminating the system's steady-state error. Finally, this module outputs a precisely conditioned control signal and sends it to the subsequent amplifier module to control the final power output.

[0040] The push-pull amplifier circuit module, as follows: Figure 11 As shown, this circuit is a high-power, high-voltage Class AB push-pull amplifier with a composite feedback design. Its core function is to amplify the low-voltage input signal with high fidelity to drive loads requiring high voltage swing. During operation, operational amplifier U25 acts as a pre-amplifier error amplifier, comparing the input signal with the feedback signal from the final stage output. Its output signal then drives a differential voltage amplifier stage (VAS) composed of Q7 and Q8, amplifying the signal voltage gain and performing level conversion. This output stage is a three-stage composite push-pull structure: the upper part is driven by Q3 to pull current from the floating ground positive high-voltage power supply RF16 (push); the lower part is driven by Q4 to pull current into the floating ground negative high-voltage power supply RF17 (pull). Diodes and other components in the circuit form a bias network to set the output stage quiescent current, eliminating crossover distortion and ensuring high fidelity in Class AB operating mode. Ultimately, the module outputs a drive voltage and current with the same waveform as the input control signal but significantly amplified in power, which is then directly applied to the final load or device under test, thereby achieving precise, rapid, and powerful control of the load state. The accuracy, noise, and dynamic performance of the entire system largely depend on the performance of the error amplifier.

[0041] To meet these stringent requirements, rail-to-rail operational amplifiers are typically chosen, employing internal self-calibration techniques to eliminate offset voltage and its drift. For ultra-low current measurements, JFET or CMOS input stage operational amplifiers must be used to obtain input bias currents in the pA or even fA range.

[0042] The circuits of the DAC and ADC modules are as follows: Figure 12As shown, the system includes: a digital control interface subsystem employing a hierarchical dual-bus architecture, wherein an I2C bus is coupled to a PCF8575 I / O expander for decoding low-frequency configuration commands into parallel control signals; and an SPI bus for high-throughput data transmission. A digital-to-analog converter (DAC) subsystem includes an AD converter communicatively coupled to the SPI bus, with its output buffered by an operational amplifier. An analog-to-digital converter (ADC) subsystem includes an ADC, also communicatively coupled to the SPI bus, for high-resolution data acquisition.

[0043] The digital-to-analog converter (DAC) subsystem further includes a novel, digitally programmable analog bias circuit. This circuit, consisting of a voltage offset circuit composed of precision operational amplifiers, generates an analog bias voltage that is proportional to, electrically isolated, stable, adjustable, and symmetrically oriented within a positive and negative range, relative to the digital control signal.

[0044] According to the aforementioned system, a proportional measurement architecture is employed to achieve high accuracy and high stability. A highly stable precision voltage reference (VREFERENCE2) is used as a common reference source, and its reference voltage output is simultaneously provided to the reference input pins of both the DAC and the ADC. By allowing the excitation generation (DAC) and response measurement (ADC) to share the same reference voltage, any drift or absolute error generated by the reference source is suppressed by the common mode, thus ensuring that the overall accuracy of the system depends primarily on the matching degree of the internal passive components rather than the absolute accuracy of the reference voltage.

[0045] When performing high-impedance measurements (e.g., measuring currents below 1 nA), minute leakage currents from surrounding circuitry can become a major source of error. These leakage currents can flow through air, PCB surface contaminants, or cable insulation. To eliminate these leakage currents, this invention employs "Driven Guard" technology.

[0046] On the PCB layout, a copper trace called the "Guard Ring" completely surrounds the high-sensitivity input signal trace (e.g., the trace connected to the inverting input of an error amplifier). This Guard Ring connects to the Guard output. When using an external cable to connect the DUT, a triaxial cable should be used. The center conductor of the cable transmits the signal, the inner shield is connected to the Guard output, and the outermost shield is grounded (for electrostatic discharge protection).

[0047] Due to the action of the Guard buffer, the potential of the protective conductors (guard ring and inner shield) is actively driven to the same potential as the signal line. According to Ohm's law, since the voltage difference between the signal line and the guard conductor is zero, no leakage current will flow even though there is a finite insulation resistance between them. Any leakage current that might flow from the surrounding high-voltage source will be absorbed by the low-impedance Guard circuit without contaminating the high-impedance measurement signal.

[0048] While the analog control loop of this invention achieves fast and stable local regulation, its setpoint and clamping values ​​are provided by a high-resolution digital-to-analog converter (DAC), typically 16-bit or higher precision. Simultaneously, the actual output voltage and current are measured by one or more high-resolution analog-to-digital converters (ADCs), typically 24-bit or higher precision, to ensure measurement resolution and accuracy.

[0049] This digital monitoring and control layer enables the measurement system to perform complex test sequences, such as voltage / current scans, pulse outputs, and data logging. In more advanced architectures, the entire control loop, including error calculation and compensation, can be implemented in the digital domain. This fully digital loop allows for dynamic adjustment of the loop's response characteristics via software programming to optimize for loads with different characteristics, thereby achieving the best balance between speed and stability.

[0050] Although high-precision analog components are used in the design, inherent errors such as nonlinearity errors of the DAC and ADC, resistor tolerances and temperature drift, and amplifier offset will still accumulate and affect the absolute accuracy of the system. Therefore, system-level calibration is essential.

[0051] Calibration is typically performed during manufacturing or routine maintenance. The system's output is connected to a higher-precision calibration standard instrument (e.g., an 8.5-digit digital multimeter) and a precision standard resistor. The system's internal controller instructs its output to display a series of nominal voltage and current values ​​while simultaneously recording the readback values ​​from its own ADC and the calibration standard instrument. By comparing these two sets of data, a series of calibration coefficients (typically gain and offset correction values) can be calculated.

[0052] These calibration coefficients are stored in the system's non-volatile memory. During normal operation, the SMU's firmware applies these correction coefficients in real time before sending the setpoint to the DAC and after reading the measurement value from the ADC, digitally compensating for systematic errors in the analog circuitry. This process ensures that the SMU's output and measurement results are traceable to metrological standards, thus guaranteeing the high accuracy specified in its datasheet.

[0053] This hybrid system design, deeply integrating analog and digital technologies, is a hallmark of modern high-performance measurement equipment. The analog front-end provides low-noise, high-bandwidth raw signal processing capabilities, while the digital back-end provides flexibility, intelligence, and the final accuracy achieved through calibration. Both complement each other and are indispensable.

[0054] The connection relationship of each module of the measurement system of this invention is as follows: When the switching power supply module is turned on and supplies power to the system, the Raspberry Pi 5, as the main control host computer, controls the switching chip and switching relay through IIC to select either the applied voltage measurement circuit (FVMI) or the applied current measurement voltage mode (FIMV) (the two loop operating modes are as follows). Figure 2 Figure 3 (As shown). The Raspberry Pi 5 then controls the DAC and ADC modules via SPI communication, converting the received digital signals into analog signals. The three DAC output signals are connected to the clamping and integrating circuit module to generate precise control signals in the closed-loop feedback system. The clamping and integrating circuit module transmits signals to the push-pull amplifier circuit module. The amplifier circuit module works with the floating power supply module to drive the voltage and current on the load. The current detection module works with the mode and range selection module to use an automatic gain control algorithm (such as...). Figure 4 As shown, the system automatically selects different sampling resistors to obtain the current; the voltage detection module measures the voltage difference across the load; the electrical signals obtained from the current and voltage detection modules are selectively connected to the clamping and integrating circuit modules according to whether FVMI or FIMV mode is selected, thus forming a closed-loop control. In the DAC and ADC modules, the ADC receives the output signals from the current and voltage detection modules, converts the electrical signals into digital signals, and sends them to the Raspberry Pi 5 host computer via the SPI protocol for real-time communication and adjustment.

[0055] This invention discloses a high-precision, wide-range DC parameter measurement system, aiming to solve the technical problems of high cost and difficulty in simultaneously achieving testing accuracy and stability in existing semiconductor parameter testing and material property analysis applications. By adopting the technical solution of this invention, the following significant beneficial effects can be achieved: 1. It achieves high-precision four-quadrant source and measurement functions, with excellent technical performance indicators.

[0056] The core of this invention lies in its precise closed-loop feedback control system. The voltage / current detection module employs a precision differential amplifier circuit with a protection ring drive, effectively suppressing leakage current and common-mode noise interference in the measurement of minute signals. Combined with a clamping and integration control module based on operational amplifiers and precision resistor networks, the stability and accuracy of the output are ensured.

[0057] Scientific analysis and experimental results demonstrate that, as verified by prototype testing, in voltage source mode, the output voltage range of this invention reaches ±120V, with a setting accuracy of ±(0.1% of the set value + 500μV) and a readback measurement accuracy better than ±(0.1% of the reading + 100μV). In current source mode, the output current range reaches ±150mA, with a minimum controllable current resolution of 0.1nA, and a measurement accuracy better than ±(0.05% of the reading + 600pA) in the 1mA range. These specifications are sufficient to meet the precise testing requirements of static parameters (such as leakage current, threshold voltage, and transconductance) of modern semiconductor devices (such as MOSFETs and IGBTs) and high-resistivity materials, demonstrating significant technical effectiveness.

[0058] 2. Seamless automatic range switching with a wide dynamic range is achieved, greatly improving testing efficiency.

[0059] To address the issue of manual range switching or programmable range switching pauses required by traditional instruments when testing devices with large dynamic ranges, the range selection module of this invention employs a combination of multi-channel analog switches and high-speed relays. This solution enables automatic and rapid smooth switching between multiple ranges ranging from microamps (μA) to amperes (A) based on real-time measurement values, dictated by control logic.

[0060] Specific data shows that when performing a logarithmic current scan test from 1μA to 100mA on a device, the seamless automatic range switching function of this invention reduces the total test time from approximately 2.5 seconds using the traditional programmable range switching method to less than 0.1 seconds, significantly improving test efficiency. This technological effect has significant economic value for scenarios requiring large-scale, rapid parameter scanning, such as wafer-level testing and device aging screening, and can significantly shorten product development cycles and reduce production and testing costs.

[0061] 3. The circuit structure is highly integrated and the cost is controllable, resulting in significant economic and social benefits.

[0062] This invention ensures high performance while fully considering the economic aspects of the design. For example, the power supply section adopts an innovative transformerless dual-channel high and low voltage DC power supply scheme, which greatly reduces the product's size, weight, and material costs compared to traditional linear transformer power supplies. The overall circuit design is compact, highly integrating complex analog front-end functions.

[0063] Cost analysis shows that the technical solution of this invention reduces the bill of materials (BOM) cost of the entire machine by 50%-60% compared to purchasing commercial equipment with equivalent performance. This enables universities, research institutions, and small and medium-sized technology enterprises to build advanced testing platforms at an affordable cost, lowering the threshold for scientific research and innovation and yielding positive social benefits.

[0064] 4. Enhanced system stability and reliability, ensuring the safety of equipment and devices under test.

[0065] In this invention, the clamping circuit design ensures that the control signal is always within a safe range, effectively preventing output overshoot caused by integral saturation. It protects the device under test (DUT) from electrical stress damage during power-on, range switching, and sudden load changes. Simultaneously, the comprehensive electrostatic and overvoltage protection designs of each module enhance the long-term operational reliability of the SMU itself.

[0066] The test results show that in the load change test from no-load to full-load at the output terminal, the overshoot of the output voltage is effectively suppressed to within 10mV, and the response recovery time is less than 200μs, demonstrating excellent robustness. This inherent technical effect ensures the consistency and repeatability of the test results and reduces economic losses caused by equipment or device under test damage.

[0067] In summary, this invention has successfully developed a testing device that integrates high precision, wide range, high efficiency, low cost, and high reliability through a series of innovative technical solutions. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of the semiconductor DC parameter testing system of the present invention.

[0069] Figure 2 This is a schematic diagram of the FVMI model of the present invention.

[0070] Figure 3 This is a FIMV mode diagram of the present invention.

[0071] Figure 4 This is a flowchart of the automatic gain algorithm in this invention.

[0072] Figure 5 This is a circuit diagram of the switching power supply module in this invention.

[0073] Figure 6 This is a simplified circuit diagram of the floating ground power supply module in this invention.

[0074] Figure 7 This is a simplified circuit diagram of the voltage detection module in this invention.

[0075] Figure 8 This is a simplified circuit diagram of the current detection module in this invention.

[0076] Figure 9 This is a simplified circuit diagram of the mode and range selection module in this invention.

[0077] Figure 10 This is a simplified circuit diagram of the clamping and integrating circuit module in this invention.

[0078] Figure 11 This is a simplified circuit diagram of the push-pull amplifier module in this invention.

[0079] Figure 12 This is a simplified circuit diagram of the DAC and ADC modules in this invention. Detailed Implementation

[0080] The measurement system provided by this invention includes: a Raspberry Pi 5, a power module, a floating power module, a voltage detection module, a current measurement module, a mode and range selection module, a clamping and integration circuit module, a push-pull amplifier circuit module, a DAC and ADC module, and a signal transmission port; the modules are connected to a double-layer PCB board via terminals or pins.

[0081] Example: FVMI mode (apply voltage and measure current) 1. System Initialization and Mode Selection: After the system is powered on, the power module provides stable DC and AC power to each functional module. The host Raspberry Pi 5 sends commands to the I / O expansion chip via its GPIO port using the I2C bus protocol. This chip controls the DG series switching chips and other signal relays to operate, configuring the system loop in FVMI mode. In this mode, the output of the voltage detection module is used as a feedback signal to connect to the clamping and integrating circuit module, forming a voltage closed loop.

[0082] 2. Parameter setting and signal generation: The test program runs on Raspberry Pi 5 and sends digital codes to a high-precision digital-to-analog converter (DAC) via the SPI bus protocol to set the target output voltage range; the DAC converts the digital codes into high-precision analog voltage signals.

[0083] 3. Closed-Loop Control and Power Drive: The setting signal output by the DAC (including the amplified signal from the circuit and the signals at both ends of the clamping circuit) and the real-time load voltage signal fed back from the voltage detection module are simultaneously input to the clamping and integrating circuit module. The operational amplifier in this module integrates the difference between the two signals and outputs a control signal to the amplification circuit module. The amplification circuit module uses a push-pull circuit for amplification and is powered by a floating ground power supply module.

[0084] 4. Current Measurement and Data Acquisition: At this point, the current flowing through the load enters the current detection module. The automatic gain algorithm running on the Raspberry Pi 5 (such as...) Figure 4 As shown, the current level is determined, and the analog switch in the range selection module is automatically switched via I2C commands to select a high-precision sampling resistor. The voltage drop across this resistor is amplified by the precision differential amplifier of the current detection module and then sent to a high-resolution analog-to-digital converter (ADC). The ADC converts the analog signal into a digital signal and sends it back to the Raspberry Pi 5 via the SPI bus.

[0085] The FIMV mode is similar to the above process, except that the switch gating is changed to select different system loops.

[0086] In voltage source mode, the output voltage range of this invention reaches ±120V, with a setting accuracy of ±(0.1% of the set value + 500μV) and a readback measurement accuracy better than ±(0.1% of the reading + 100μV). In current source mode, the output current range reaches ±150mA, with a minimum controllable current resolution of 0.1nA and a measurement accuracy better than ±(0.05% of the reading + 600pA) at a 1mA range. These specifications are sufficient to meet the precise testing requirements of static parameters (such as leakage current, threshold voltage, and transconductance) of modern semiconductor devices (such as MOSFETs and IGBTs) and high-resistivity materials, demonstrating significant technical advantages.

Claims

1. A Raspberry Pi-based semiconductor DC parameter test system adopts multiplexing high-precision analog loop and multi-stage parameter calibration algorithm, characterized in that, The application relates to a high-precision multi-channel power supply test platform, which comprises the following: a Raspberry Pi, a switching power supply module, a floating ground power supply module, a voltage detection module, a current detection module, a mode and range selection module, a clamping and integration circuit module, a push-pull amplification circuit module, a DAC and ADC module and a signal transmission port; each module is connected on a PCB through a high-shielding signal port mode; wherein: the Raspberry Pi serves as a core controller and a data processing center, controls external precision analog circuits (ADC / DAC) through a GPIO, SPI or I2C interface to complete voltage / current output and measurement, is responsible for running a test process, processing data, providing human-computer interaction and network communication functions, and adopts a multi-level parameter calibration algorithm to construct an open-source intelligent test platform in a low-cost and high-flexibility mode; the switching power supply module is used for room voltage conversion and provides commonly-used stable direct-current power and high-voltage alternating-current power, is used for power supply of each circuit on the circuit board and provides large-power driving; the switching power supply module adopts a flyback topology and has multi-way output and basic protection functions; the switching power supply module is composed of an input stage circuit, an output stage circuit, a switching part circuit, a control and feedback loop and an auxiliary and protection circuit; the floating ground power supply module is used for providing positive and negative high and low voltage stable isolation direct-current power and is used for driving the amplification circuit module to generate a voltage difference; the circuit comprises a high-voltage rectification and filtering module and a low-voltage capacitor voltage reduction and stabilization module; the voltage detection module is used for measuring the voltage of a device to be measured or a load and performing proportional voltage compression on the voltage, and the voltage is fed back to the integration circuit module through mode selection; the current detection module is used for measuring the current of the device to be measured or the load, converting the current size into a current size through serial resistance voltage measurement, and feeding back to the integration circuit module through mode selection; the mode and range selection module is used for automatically detecting different precision currents and applying different precision currents through an array; the clamping and integration circuit module is used for limiting the initial input voltage range, reducing system errors, making the system a closed-loop system, protecting the circuit and generating an accurate control signal in the closed-loop feedback system; the push-pull amplification circuit module is used for power amplification of a front-stage control signal and drives external loads in a high-efficiency and low-distortion mode; the module serves as a power output stage and provides bidirectional current driving capability, that is, supplies power to the load and absorbs power from the load; the DAC and ADC module is used for converting a set digital signal into a voltage signal and acquiring an electric signal to convert the electric signal into a digital signal and send the digital signal to an upper computer while controlling switch selection; the signal transmission port is a coaxial radio frequency port and is used for important signal transmission between modules and the system. In the switching power supply module: the input stage circuit mainly functions to perform EMI filtering and rectification on the alternating-current input; wherein the input is alternating-current input, overcurrent protection is provided through a fuse; startup inrush current is inhibited through a negative temperature coefficient thermistor, common mode / differential mode interference is filtered through an anpro capacitor, and high-frequency noise is further inhibited through a common mode inductor; the alternating current is converted into pulsating direct current through a rectifier bridge, and a high-voltage electrolytic capacitor is used as a main direct-current bus capacitor to smooth the voltage after rectification. ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The test system of claim 1, wherein, ​ ​ The output stage circuit, the main function is rectification and filtering and provide multi-output; By Schottky diode for secondary rectification, low on-state voltage drop reduces loss; By electrolytic capacitor smoothing output voltage, by LC filter network and capacitor combination further inhibit high frequency ripple; Multi-voltage output, by linear voltage regulator to generate low voltage, for low power load; Higher DC output directly through the secondary winding rectification filter, by LED indicator light through the current limiting resistor display power state; The switching part circuit, its core element is PWM controller, power switch tube and high frequency transformer; The control and feedback loop, including voltage stabilizer through the voltage dividing resistor set output voltage; When the output voltage rises, the stabilizer cathode current increases → the light coupling internal LED brightness increases → the light coupling transistor side conduction enhances → the DC-DC power supply chip pin voltage drops → duty cycle reduces, realizes closed loop regulation; Compensation adopts Type II compensation, capacitor provides integral action, reduces high frequency gain; Resistance adjusts zero point frequency, promotes phase margin; Capacitor suppresses high frequency noise, together ensures loop stability; The overcurrent protection circuit, through the current detection resistor detects main loop current, signal is sent into DC-DC power supply chip through pin; When the current exceeds threshold value, PWM output is closed, realizes period-by-period current limiting; Auxiliary power supply circuit is powered by 15V_AUX for power supply chip, is generated by transformer auxiliary winding through diode rectification and capacitor filtering.

3. The test system of claim 1, wherein, In the floating ground power module: The high voltage rectification and filtering module, through the bridge rectifier circuit composed of four diodes to full-wave rectify the input alternating current, and utilize two filter capacitors in series to smooth the pulsed direct current after rectification, to establish a symmetrical high voltage positive and negative direct current power supply and a common reference ground; The low voltage capacitor voltage reduction and stabilization module, through the capacitor voltage reduction circuit composed of two capacitors and two resistors to limit current and reduce voltage, after processing through two rectifier elements, utilize two voltage stabilizing diodes to clamp the voltage at a preset + / - 15V, and finally through two filter capacitors to output smooth and stable low voltage direct current; In addition, the circuit is also provided with a working state indication circuit composed of two light emitting diodes and their current limiting resistors, for directly displaying the working state of the high voltage power supply.

4. The test system of claim 1, wherein, In the voltage detection module, the differential voltage signal from both sides of the load is first passed through the channel selection circuit composed of two relays, and then is proportionally reduced through the precision voltage dividing resistor network, for adjusting the high voltage input to the processing range of the subsequent circuit; The reduced signal is sent to the differential subtractor circuit composed of precision operational amplifier U12A and peripheral resistors, for accurately extracting the voltage difference of the two input signals; At the same time, another operational amplifier U12B generates a protection ring signal, for shielding high impedance nodes to reduce leakage current interference; Subsequently, the signal output by the subtractor enters the multi-channel analog switch composed of U11, for selecting between the measurement signal and the calibration reference; Finally, the selected signal is subjected to final stage buffering and conditioning by the instrument amplifier U10, and is output to the external data acquisition system.

5. The test system of claim 1, wherein, The current detection module, the current to be measured passes through the path controlled by the relay, selectively flows through the sampling resistor with high precision and low resistance, and different resistors are selected according to the current range to generate a differential voltage; the tiny differential voltage signal between the two ends of the sampling resistor is sent to the precision differential amplification front-end circuit composed of the operational amplifier U21 for high-precision extraction and preliminary amplification; then, the signal is subjected to main gain amplification by the secondary differential amplification circuit composed of the operational amplifier U20.1, and is converted into a voltage value proportional to the measured current and easy to measure; at the same time, the protection ring driving circuit composed of another operational amplifier U20.2 generates a protection signal to shield the high-impedance input node, so as to reduce the interference of the leakage current and noise on the measurement accuracy.

6. The test system of claim 1, wherein, The mode and range selection module adopts a multi-range current detection scheme, that is, a plurality of precision shunt resistors with different resistances are arranged in the high-side path of the output current, and according to the size of the current to be measured, a suitable shunt resistor is selected to be connected to the circuit through a low-leakage relay or a special analog switch; the circuit includes a sampling resistor network composed of a plurality of precision resistors connected in series, and two four-channel analog switches controlled by external logic signals; the two analog switches work cooperatively to connect different voltage sampling point pairs on the sampling resistor network according to different range selection instructions, change the equivalent resistance value between the sampling point pairs, and realize the switching of a plurality of precision current measurement ranges from microamperes to milliamperes; in addition, the circuit further includes a large-current range controlled by a relay, which is used to bypass the precision resistor network and switch to an independent low-resistance shunt when measuring larger currents.

7. The test system of claim 1, wherein, The clamping and integration circuit module receives the set value signal from the digital-to-analog converter (DAC) and the feedback signal from the voltage detection module, and calculates an error signal through a differential circuit composed of an operational amplifier and a precision resistor; the clamping circuit composed of a diode or a zener diode is used to limit the error signal or the integration result in a preset safe voltage range, so as to prevent system saturation and overshoot; then, the signal is sent to an integration circuit with an operational amplifier as the core and provided with an integration capacitor and an input resistor, which integrates the error signal by using the charge and discharge characteristics of the capacitor to eliminate the steady-state error of the system; finally, an accurately conditioned control signal is output and sent to the amplification circuit module in the later stage to control the final power output.

8. The test system of claim 1, wherein, The push-pull amplification circuit module receives the accurate control signal from the clamping and integration circuit module, which is composed of a pair of complementary and symmetrical power transistors connected to the positive and negative power rails respectively; the pair of transistors work alternately according to the polarity of the input control signal: when one of the transistors is driven to be turned on by the input signal, the current flows from the power supply to the load to realize power supply; when the other transistor is driven to be turned on by the input signal, the current flows from the load to the power supply to realize power absorption; The module also integrates a bias circuit for setting a small static working current for the pair of complementary power transistors, so as to work in class AB state, to overcome the threshold voltage of the transistor, so as to eliminate the crossover distortion that may be generated when the signal switches near zero, and to ensure the continuity and high linearity of the output signal in the entire dynamic range; Finally, the module outputs a driving voltage and current with the same waveform as the input control signal but with a significantly amplified power, and directly applies it to the final load or measured device, to realize accurate, fast and powerful control over the load state.

9. The test system of claim 1, wherein, The DAC and ADC module comprises: A digital control interface subsystem adopting a layered double bus architecture, wherein the I2C bus is coupled to the I / O expander for decoding low-frequency configuration commands into parallel control signals, and the SPI bus is used for high-throughput data transmission; A digital-to-analog conversion (DAC) subsystem comprising an AD digital-to-analog converter communicatively coupled with the SPI bus and having its output buffered by a rail-to-rail operational amplifier; An analog-to-digital conversion (ADC) subsystem comprising an analog-to-digital converter (ADC) also communicatively coupled with the SPI bus for high-resolution data acquisition, and An analog signal routing subsystem comprising at least one analog switch controlled by the I / O expander (U2) for selectively constructing an analog signal path according to I2C commands.

10. The test system of one of claims 1-10, wherein, The relationship between the modules is as follows: When the switching power supply module is turned on and supplies power to the system, the Raspberry Pi as the host computer controls the switching chip and the switching relay through IIC to select the application of the voltage measurement circuit (FVMI) or the application of the current measurement voltage mode (FIMV); then the Raspberry Pi controls the DAC and ADC module output through the SPI communication mode, and converts the received digital signal into an analog signal; the DAC three-way output signal is connected to the clamping and integration circuit module for generating an accurate control signal in a closed-loop feedback system; the clamping and integration circuit module transmits the signal to the amplification circuit module; the amplification circuit module cooperates with the floating ground power module to drive the voltage and current of the load; the current detection module cooperates with the mode range selection module to automatically select different sizes of sampling resistors through an automatic gain algorithm, so as to obtain the current; the voltage detection module is used for measuring the voltage difference across the load; the current detection and voltage detection modules selectively access the clamping and integration circuit module according to the FVMI or FIMV mode selection, so as to form a closed-loop control; the ADC in the DAC and ADC module receives the output signal from the current detection and voltage detection modules, converts the electrical signal into a digital signal, and sends it to the Raspberry Pi 5 host computer through the SPI protocol for real-time communication and adjustment.

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