## 3 Circuit Simulation and Experiment  
Simulation and experimental circuits for the PDSH circuit are constructed, according to Figure 2. Considering the measurement of nanosecond-scale pulse peak, OTA should  
Figure 4: The equivalent circuit model of the diode during the voltage step process. possess features of high bandwidth, high slew rate, and low delay. In this paper, the OPA615 chip is selected as the OTA to construct the PDSH circuit. The parameters \(g\), \(V_{th}\), \(I_{om}\), and \(k\) can be obtained by DC scanning of the OPA615 by using the simulation software. Following that, the diode uses the simulation model of 1N4148. The simulation circuit diagram of the PDSH circuit in PSpice is shown in Figure 5.  
The schematic diagram and experiment diagram of the overall system are shown in Figures 6 and 7, respectively. The pulse signal is generated by the signal generator RIGOL DG4602, while employing FPGA triggering techniques to achieve pulse widths in the nanosecond range. And the power supply for the experimental PCB board is provided by the DC power supply RIGOL DP831, while the signal measurements are performed using the oscilloscope Agilent DSO7104B. After the completion of the PDSH circuit measurement, in order to measure the peak value of a single pulse signal, the FPGA was utilized to control the discharge of the sampling capacitor through the MOSFET. This discharge was performed to prevent any interference from the previous measurement, ensuring the accuracy and reliability of the current measurement. Furthermore, OrCAD Capture 16.6 (PSpice) software was also used to verify the results of the model. Figure 5: The simulation circuit diagram of the PDSH circuit in PSpice. Figure 6: The diagram for the simulation and experiment of the overall system. Figure 8 illustrates the dynamic measurement process of the PDSH circuit with \(C_{h}=30\) pF, \(t_{r}=10\) ns, and \(V_{m}=1\) V. Since the maximum output current of OPA615 is 5 mA, which satisfies (11), the output voltage of the PDSH circuit can keep up with the input signal variation. The horizontal axis represents time, while the vertical axis represents voltage. The simulation results indicate that the difference between the input and output voltages is always smaller than the threshold voltage, shown as (b), which is consistent with the theoretical prediction. Figure 8: (**a**) The change in output voltage of the PDSH circuit when (11) is satisfied (**b**) The variation of the difference between the input voltage and the output voltage of the PDSH circuit. Figure 7: The system configuration diagram for the PDSH circuit measurement experiment. Figure 9 illustrates the dynamic measurement process of the PDSH circuit with \(C_{h}=30\) pF, \(t_{r}=10\) ns, and \(V_{m}=3\) V. The horizontal axis represents time, while the vertical axis represents voltage. Based on the fact that the charging rate \(I_{on}/C_{h}\) of the sampling capacitor is smaller than the rising rate \(V_{m}/t_{r}\) of the input signal, the difference between the input and output voltages will be greater than the threshold voltage. Therefore, the PDSH circuit needs to spend a certain amount of time to accurately measure the peak value of the pulse, according to the theory. Figures 8 and 9 also show that the slew rate of the OTA is lower than the rise rate of the input signal. Although the OTA will charge the capacitor at the maximum output current at this time, the output voltage of the PDSH circuit still cannot keep up with the input signal. The measurement speed of the PDSH circuit can also be characterized by the rising time of the output voltage. The derivative of the output voltage with respect to time reflects the instantaneous measurement speed of the PDSH circuit, while the rising time can reflect the average measurement speed. In this paper, the Simulink tool in MATLAB was used to model the measurement process of the PDSH circuit. Simulink allows the insertion of delay modules, which enables a more precise description of the measurement process of the PDSH circuit.