Study on the influence of temperature on Spice diode characteristics based on Matlab

Spice is a powerful general-purpose analog circuit simulator and a circuit analysis program mainly used to simulate integrated circuits. In the Spice program, there are two methods to establish device models. One is to establish a model based on the physical principle of the device; the other is to establish a model based on the input/output external characteristics. The diode physical model in the Spice program is a model based on the physical principle of the diode. At the same time, the diode is the simplest structure among semiconductor devices. There are 14 model parameters for the diode in the Spice program, many of which are functions of temperature. This paper takes the D1N4002 diode model as the object, and studies the influence of temperature changes on the volt-ampere characteristics and equivalent capacitance of the physical model of the diode in the Spice program in the simulation environment of the software Matlab. At the same time, this research method can also be used to study the characteristics of other more complex semiconductor devices.

1 Establishment of the physical model of the diode in the Spice program

In the Spice program, the schematic diagram of the physical model of the diode is shown in Figure 1, where Rs is the material resistance of the diode, called ohmic resistance; CD is the equivalent capacitance caused by the charge storage effect; ID is a nonlinear current source.

The relationship between the nonlinear current source ID and the voltage UD applied across it is as follows:

Where: Is is the saturation current (unit: A); q is the electron charge (1.062×10-19C); K is the Boltzmann constant (1.38×10-23J/K); T is the thermodynamic temperature (unit: K); n is the emission coefficient (1.2~2.0 for silicon tube); VB is the reverse breakdown voltage (unit: V); IVB is the current during reverse breakdown (unit: A). The Spice program adds a small conductance Gmin to the PN junction of the diode. Its implicit value is 10-12S. Under normal circumstances, the existence of Gmin will not affect the normal characteristics of the diode. The

charge storage effect of the diode includes two parts. One part is the charge stored on the PN junction barrier capacitance, which is equal to the integral of the barrier capacitance to the PN junction voltage; the other part is the charge storage formed by the injection of minority carriers, which is proportional to the forward current. The total charge storage QD is:

Where: τD is the transit time of minority carriers; Cjo is the depletion layer capacitance of the PN junction at zero bias; φD is the self-built potential of the PN junction, and the typical value for the junction diode is 0.7~0.8 V; FC is the coefficient of the forward bias depletion capacitance formula, and the typical value is 0.5.

The diode equivalent capacitance CD is composed of two parts: one is the diffusion capacitance Cs generated by the charge storage injected by minority carriers, and the other is the depletion capacitance Cd generated by the charge storage of the PN junction depletion layer, namely:


2 The influence of temperature change on the volt-ampere characteristics of the Spice diode model D1N4002

A total of 14 diode model parameters are set in the Spice program. The parameters of the Spice diode model D1N4002 are shown in Table 1. These parameters are the values ​​at room temperature (27℃).

The above formulas are all calculated at room temperature, which is 27℃ (300 K) in the Spice program. However, many parameters in semiconductor devices are functions of temperature. In order to reflect the changes of parameters with ambient temperature, the Spice program provides temperature correction formulas for some parameters, such as Is, φD, CD, etc. The temperature correction formula for IS is:

For junction diodes, pt=3. For silicon diodes, Eg(300)=1.11eV.

Under the diode physical model, considering the influence of temperature on IS, the volt-ampere characteristic curve of the diode physical model is corrected using formula (10). Based on the

D1N4002 diode physical model, the diode volt-ampere characteristic curves at three temperatures of T1=300 K, T2=325 K, and T3=350 K are selected for comparative analysis.

Enter the instruction code of the volt-ampere characteristic curve of the simulated diode physical model in the command box of the simulation software Matlab, and obtain the diode volt-ampere characteristic curve as shown in Figure 2. The simulation test experimental measurement data is shown in Table 2. This is a set of volt-ampere characteristic curves of the D1N4002 diode physical model at different temperatures. It can be clearly seen from the simulation curve that the change in temperature has no obvious effect on the volt-ampere characteristic curve section of the diode reverse bias but not broken down. This is because the parameter values ​​of IS and Gmin are very small, making the ID value on this curve section approach zero. It can be concluded from the diode forward bias curve in the figure that when the diode is forward biased, the increase in temperature will cause the diode's turn-on voltage Uon to decrease, and at the same time increase after forward conduction. When the diode is reverse biased and in a Zener breakdown state, it can be seen from the curve that as the temperature increases, the diode's reverse breakdown voltage VB decreases, and increases after reverse breakdown.

3 Effect of temperature change on equivalent capacitance of Spice diode model D1N4002

The temperature correction formulas for φD and CD in Spice program are:

Under the diode physical model, considering the effect of temperature on IS and φD, the relationship curve between equivalent capacitance CD and UD of the diode physical model is corrected using equations (10) and (11). Based on the D1N4002 diode physical model, the curves of equivalent capacitance CD changing with UD at three temperatures of T1=300 K, T2=325 K, and T3=350 K are selected for comparative analysis.

In the command box of the simulation software Matlab, input the instruction code for simulating the change of equivalent capacitance of the physical model of the simulated diode with voltage UD, and obtain the curve of the change of diode equivalent capacitance with voltage UD as shown in FIG3 . The simulation test experimental data is shown in Table 3.

This is a set of curves showing the change of diode equivalent capacitance with UD at different temperatures.

Combined with the analysis of the volt-ampere characteristic curve of the diode physical model in Figure 2, it can be seen from Figure 3 that since the current flowing through the diode is very small and almost negligible when the diode is reverse biased and not reversely broken down, the equivalent capacitance of this section approaches zero, and the temperature change has a very small effect on the equivalent capacitance curve in this section. When forward conduction or reverse breakdown occurs, the current flows through the diode, and the equivalent capacitance of the diode increases sharply with the increase of UD.

When the temperature rises, the equivalent capacitance of the diode increases, and the value of also increases with the increase of temperature, and the slope of the equivalent capacitance curve is positively correlated with.

4 Conclusion

The change of temperature has little effect on the volt-ampere characteristics and equivalent capacitance of the diode in the reverse biased non-breakdown or forward biased non-conduction state, which can be almost ignored. However, in the forward conduction and reverse Zener breakdown states, the change of temperature has a significant effect on the volt-ampere characteristics and equivalent capacitance of the diode physical model. The increase in temperature causes the turn-on voltage and reverse breakdown voltage of the diode physical model to increase, the current to increase, and the rate of change of the current to the voltage UD in the volt-ampere characteristic curve to increase. The increase in temperature also causes the equivalent capacitance of the diode to increase, and the rate of change of the equivalent capacitance of the diode to the voltage UD to increase.