# SPICE Diode

Model SPICE-compatible diode

## Library

SPICE-Compatible Components/Semiconductor Devices

## Description

The SPICE Diode block represents a SPICE-compatible diode.

The SPICE Diode block model includes the following components:

### Current-Voltage Model

The block provides the following relationship between the diode current Id and the diode voltage Vd after adjusting the applicable model parameters for temperature.

Applicable Range of Vd ValuesCorresponding Id Equation

${V}_{d}>80*{V}_{t}$

${I}_{d}=IS\left(\left(\frac{{V}_{d}}{{V}_{t}}-79\right){e}^{80}-1\right)+{V}_{d}*G\mathrm{min}$

$80*{V}_{t}\ge {V}_{d}\ge -3*{V}_{t}$

${I}_{d}=IS*\left({e}^{{V}_{d}/{V}_{t}}-1\right)+{V}_{d}*G\mathrm{min}$

$-3*{V}_{t}>{V}_{d}\ge -BV$

${I}_{d}=-IS\left(1+\frac{27}{{\left({V}_{d}/{V}_{t}\right)}^{3}{e}^{3}}\right)+{V}_{d}*G\mathrm{min}$

${V}_{d}<-BV$

$\begin{array}{l}{I}_{d}=-IBV*\left({e}^{\left(-\left(BV+{V}_{d}\right)/{V}_{t}}-1\right)-\\ \text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}IS*\left(1-{\left(\frac{3}{e*BV}{{V}_{t}}}\right)}^{3}\right)+{V}_{d}*G\mathrm{min}\end{array}$

Where:

• IS is the Saturation current, IS parameter value.

• ${V}_{t}=N*k*T/q$

• N is the Emission coefficient, ND parameter value.

• q is the elementary charge on an electron.

• k is the Boltzmann constant.

• T is the diode temperature:

• If you select `Device temperature` for the Model temperature dependence using parameter, T is the sum of the Circuit temperature value plus the Offset local circuit temperature, TOFFSET parameter value. The Circuit temperature value comes from the SPICE Environment Parameters block, if one exists in the circuit. Otherwise, it comes from the default value for this block.

• If you select `Fixed temperature` for the Model temperature dependence using parameter, T is the Fixed circuit temperature, TFIXED parameter value.

• GMIN is the diode minimum conductance. By default, GMIN matches the Minimum conductance GMIN parameter of the SPICE Environment Parameters block, whose default value is 1e–12. To change GMIN, add a SPICE Environment Parameters block to your model and set the Minimum conductance GMIN parameter to the desired value.

• BV is the Reverse breakdown voltage, BV parameter value.

### Junction Charge Model

The block provides the following relationship between the diode charge Qd and the diode voltage Vd after adjusting the applicable model parameters for temperature.

Applicable Range of Vd ValuesCorresponding Qd Equation
${V}_{d}${Q}_{d}=TT*{I}_{d}+CJO*VJ*\frac{1-{\left(1-\frac{{V}_{d}}{VJ}\right)}^{1-MG}}{1-MG}$
${V}_{d}\ge FC*VJ$$\begin{array}{l}{Q}_{d}=TT*{I}_{d}+\\ \text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}CJO*\left(F1+\frac{F3*\left({V}_{d}-FC*VJ\right)+\left(\frac{MG}{2*VJ}\right)*\left({V}_{d}^{2}-{\left(FC*VJ\right)}^{2}\right)}{F2}\right)\text{​}\end{array}$

Where:

• FC is the Capacitance coefficient FC parameter value.

• VJ is the Junction potential VJ parameter value.

• TT is the Transit time, TT parameter value.

• CJ0 is the Zero-bias junction capacitance CJ0 parameter value.

• MG is the Grading coefficient MG parameter value.

• $F1=VJ*\left(1-{\left(1-FC\right)}^{\left(1-MG\right)}\right)/\left(1-MG\right)$

• $F2={\left(1-FC\right)}^{\left(1+MG\right)}$

• $F3=1-FC*\left(1+MG\right)$

### Temperature Dependence

Several diode parameters depend on temperature. There are two ways to specify the diode temperature:

• When you select `Device temperature` for the Model temperature dependence using parameter, the diode temperature is

$T={T}_{C}+{T}_{O}$

where:

• TC is the Circuit temperature parameter value from the SPICE Environment Parameters block. If this block doesn't exist in the circuit, TC is the default value of this parameter.

• TO is the Offset local circuit temperature, TOFFSET parameter value.

• When you select `Fixed temperature` for the Model temperature dependence using parameter, the diode temperature is the Fixed circuit temperature, TFIXED parameter value.

The block provides the following relationship between the saturation current IS and the diode temperature T:

$IS\left(T\right)=IS*{\left(T/{T}_{meas}\right)}^{\frac{XTI}{ND}}*{e}^{\left(\frac{T}{{T}_{meas}}-1\right)*\frac{EG}{{V}_{t}}}$

where:

• IS is the Transport saturation current, IS parameter value.

• Tmeas is the Parameter extraction temperature, TMEAS parameter value.

• XTI is the Saturation current temperature exponent, XTI parameter value.

• ND is the Emission coefficient, ND parameter value.

• EG is the Activation energy, EG parameter value.

• Vt = kT/q.

The block provides the following relationship between the junction potential VJ and the diode temperature T:

$VJ\left(T\right)=VJ*\left(\frac{T}{{T}_{meas}}\right)-\frac{3*k*T}{q}*\mathrm{log}\left(\frac{T}{{T}_{meas}}\right)-\left(\frac{T}{{T}_{meas}}\right)*E{G}_{{T}_{meas}}+E{G}_{T}$

where:

• VJ is the Junction potential, VJ parameter value.

• $E{G}_{{T}_{meas}}=1.16eV-\left(7.02e-4*{T}_{meas}{}^{2}\right)/\left({T}_{meas}+1108\right)$

• $E{G}_{T}=1.16eV-\left(7.02e-4*{T}^{2}\right)/\left(T+1108\right)$

The block provides the following relationship between the junction capacitance CJO and the diode temperature T:

$CJO\left(T\right)=CJO*\left[1+MG*\left(400e-6*\left(T-{T}_{meas}\right)-\frac{VJ\left(T\right)-VJ}{VJ}\right)\right]$

where CJO is the Zero-bias junction capacitance CJ0 parameter value.

## Basic Assumptions and Limitations

The model is based on the following assumptions:

• The SPICE Diode block does not support noise analysis.

• The SPICE Diode block applies initial conditions across junction capacitors and not across the block ports.

## Dialog Box and Parameters

### Main Tab

Device area, AREA

The diode area. This value multiplies the Saturation current, IS, Zero-bias junction capacitance CJ0, and Reverse breakdown current, IBV parameter values. It divides the Ohmic resistance, RS parameter value. The default value is `1` m2. The value must be greater than `0`.

Number of parallel devices, SCALE

The number of parallel diodes the block represents. This value multiplies the output current and device charges. The default value is `1`. The value must be greater than `0`.

Saturation current, IS

The magnitude of the current that the ideal diode equation approaches asymptotically for very large reverse bias levels. The default value is `1e-14` A/m2. The value must be greater than or equal to `0`.

Ohmic resistance, RS

The series diode connection resistance. The default value is `0.01` m2*Ω. The value must be greater than or equal to `0`.

Emission coefficient, ND

The diode emission coefficient or ideality factor. The default value is `1`. The value must be greater than `0`.

### Junction Capacitance Tab

Model junction capacitance

Select one of the following options for modeling the junction capacitance:

• `No` — Do not include junction capacitance in the model. This is the default option.

• `Yes` — Specify zero-bias junction capacitance, junction potential, grading coefficient, forward-bias depletion capacitance coefficient, and transit time.

Zero-bias junction capacitance CJ0

The value of the capacitance placed in parallel with the exponential diode term. This parameter is only visible when you select `Yes` for the Model junction capacitance parameter. The default value is `0` F/m2. The value must be greater than or equal to `0`.

Junction potential VJ

The junction potential. This parameter is only visible when you select `Yes` for the Model junction capacitance parameter. The default value is `1` V. The value must be greater than `0.01` V.

The grading coefficient. This parameter is only visible when you select `Yes` for the Model junction capacitance parameter. The default value is `0.5`. The value must be greater than `0` and less than `0.9`.

Capacitance coefficient FC

The fitting coefficient that quantifies the decrease of the depletion capacitance with applied voltage. This parameter is only visible when you select `Yes` for the Model junction capacitance parameter. The default value is `0.5`. The value must be greater than or equal to `0` and less than `0.95`.

Transit time, TT

The transit time of the minority carriers that cause diffusion capacitance. This parameter is only visible when you select `Yes` for the Model junction capacitance parameter. The default value is `0` s. The value must be greater than or equal to `0`.

Specify initial condition

Select one of the following options for specifying an initial condition:

• `No` — Do not specify an initial condition for the model. This is the default option.

• `Yes` — Specify the initial diode voltage.

 Note:   The SPICE Diode block applies the initial diode voltage across the junction capacitors and not across the ports.
Initial voltage V0

Diode voltage at the start of the simulation. This parameter is only visible when you select `Yes` for the Model junction capacitance and `Yes` for the Specify initial condition parameter. The default value is `0` V.

 Note:   The block applies the initial condition across the diode junction, so the initial condition is only effective when charge storage is included, i.e. when one or both of the Zero-bias junction capacitance CJ0 and Transit time, TT parameters are greater than zero.

### Reverse Breakdown Tab

Model reverse breakdown

Select one of the following options for modeling the diode reverse breakdown:

• `No` — Don't model reverse breakdown. This is the default option.

• `Yes` — Introduce a second exponential term to the diode I-V relationship, thereby modeling a rapid increase in conductance as the breakdown voltage is exceeded.

Reverse breakdown current, IBV

The diode current that corresponds to the Reverse breakdown voltage, BV value. This parameter is only visible when you select `Yes` for the Model reverse breakdown parameter. The default value is `0.001` A/m2. The value must be greater than `0`.

 Note:   The Diode model does not use this parameter at this time.
Reverse breakdown voltage, BV

The voltage below which to model the rapid increase in conductance that occurs at diode breakdown. This parameter is only visible when you select `Yes` for the Model reverse breakdown parameter. The default value is `Inf` V. The value must be greater than or equal to `0`.

### Temperature Tab

Model temperature dependence using

Select one of the following options for modeling the diode temperature dependence:

• `Device temperature` — Use the device temperature, which is the Circuit temperature parameter value (from the SPICE Environment Parameters block, if one exists in the circuit, or the default value for this block otherwise) plus the Offset local circuit temperature, TOFFSET parameter value.

• `Fixed temperature` — Use a temperature that is independent of the circuit temperature to model temperature dependence.

Saturation current temperature exponent, XTI

The order of the exponential increase in the saturation current as temperature increases. This parameter is only visible when you select `Device temperature` for the Model temperature dependence using parameter. The default value is `3`. The value must be greater than `0`.

Activation energy, EG

The diode activation energy. This parameter is only visible when you select `Device temperature` for the Model temperature dependence using parameter. The default value is `1.11` eV. The value must be greater than or equal to `0.1`.

Offset local circuit temperature, TOFFSET

The amount by which the diode temperature differs from the circuit temperature. This parameter is only visible when you select ```Device temperature``` for the Model temperature dependence using parameter. The default value is `0` K.

Parameter extraction temperature, TMEAS

The temperature at which the diode parameters were measured. The default value is `300.15` K. The value must be greater than `0`.

Fixed circuit temperature, TFIXED

The temperature at which to simulate the diode. This parameter is only visible when you select `Fixed temperature` for the Model temperature dependence using parameter. The default value is `300.15` K. The value must be greater than `0`.

## Ports

The block has the following ports:

`+`

Positive electrical voltage.

`-`

Negative electrical voltage.