Photodiode
Photodiode with input port for incident light flux.
Description
Unit Photodiode is a photodiode in the form of a controlled current source and an exponential diode connected in parallel. The controlled current source generates a current , which is proportional to the light flux density:
where
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- is the ratio of the generated current to the incident light flux density.
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If the Sensitivity parameterization is set to `Specify measured current for given flux density', the block calculates this variable through the ratio of the Measured current parameter to the Flux density parameter.
-
If the Sensitivity parameterization is set to
Specify current per unit flux density, this variable is determined by the value of the Device sensitivity parameter.
-
-
- is the incident light flux density.
To model the dynamic response time, use the Parameterization parameters to include the diode junction capacitance in the model.
The exponential diode model provides the following relationship between diode current and diode voltage :
where
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- is the elementary charge of the electron (1.602176e-19 Kel);
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- Boltzmann constant (1.3806503e-23 J/K);
-
- emission coefficient;
-
- saturation current, corresponds to the value of the Dark current parameters.
-
- temperature, at which the diode parameters are set, corresponds to the Measurement temperature parameter value.
When ( / ) > 80, the block replaces with ( / - 79) , which corresponds to the diode current gradient at ( / ) = 80 and is extrapolated linearly.
When ( / ) < -79, the block replaces with ( / + 80) , which also corresponds to the gradient and is extrapolated linearly. Typical electrical circuits do not achieve such large values. The block Photodiode provides this linear extrapolation to aid convergence when solving constraints during simulation.
By setting the Diode parameterization parameter to Use dark current and N, the diode characteristics are set using the Dark current and Emission coefficient parameters.
If you set the Diode parameterization to Use dark current plus a forward bias I-V data point for the parameter, you must set the Dark current parameter and the voltage and current measurement point on the diode’s volt-ampere curve. The block calculates from these values as follows:
where
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- corresponds to the value of the parameter Forward voltage VF;
-
= / ;
-
- corresponds to the value of the parameter Current IF at forward voltage VF.
The exponential diode model provides an opportunity to include the junction capacitance:
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If you set the Parameterization parameters to
Fixed or zero junction capacitance, the capacitance is fixed. -
If you set the Parameterization parameter to
Use parameters CJO, VJ, M & FC, the block uses the coefficients , , , and to calculate the junction capacitance, which depends on the junction voltage. -
If the Parameterization parameters are set to
Use C-V curve data points, the block uses the three capacitance values on the C-V capacitance curve to estimate , and and uses these values with the specified value to calculate the junction capacitance that depends on the junction voltage. The block calculates , and as follows:-
-
-
,
-
where
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, , and are the values in the Reverse bias voltages [VR1 VR2 VR3] parameter vector.
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, , and are the values in the Corresponding capacitances [C1 C2 C3] parameter vector. It is not possible to reliably estimate from tabular data, so you must specify its value using the Capacitance coefficient parameter FC. If no suitable data is available for this parameter, use a typical value of 0.5.
The reverse bias voltages (numerical values are positive) must satisfy > > . This means that capacitances must satisfy > > , since reverse bias expands the depletion region and therefore reduces the capacitance. Violation of these inequalities results in an error. The voltages and must be much larger than the transition potential difference . The voltage must be less than the junction potential difference , with a typical value of 0.1 V for .
The voltage dependence of the p-n junction properties is defined through the charge of the junction capacitance as:
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For :
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For :
where
-
-
-
-
- is the voltage across the junction capacitance.
These equations are similar to those in 2, except that the temperature dependence of the parameters VJ and FC was not modelled. The diffusion capacitance term, which affects the switching performance at high frequencies, is not included in this model.
The block Photodiode includes many other possibilities for modelling the temperature dependence of the diode’s volt-ampere characteristics. The temperature dependence of the junction capacitance is not modelled due to their smallness.
Thermal port
You can enable the thermal port to simulate the effects of generated heat and device temperature. To enable the thermal port, select the check box for the Enable thermal port parameters.
Variables
To set priority and initial target values for block variables before simulation, use the Initial Targets section in the block dialogue box.
| To satisfy all initial conditions, do not set the priority to `High' for more initial variable values than the total number of differential variables in the equations. |
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If you set the Parameterization parameters in the Junction Capacitance section to
Fixed or zero junction capacitanceand the Junction capacitance parameters to0, the total number of differential variables in the block equations will be zero. Do not set the priority of the variables in the Initial Targets section toHigh. -
If you set the Parameterization parameter in the Junction Capacitance section to
Fixed or zero junction capacitanceand set the Junction capacitance parameters to a non-zero value, the total number of differential variables in the block equations is equal to one. Set the priority toHighfor no more than one variable under Initial Targets. -
If the Junction Capacitance section of Parameterization is set to
Use C-V curve data pointsorUse parameters Cj0, VJ, M & FC, the total number of differential variables in the block equations is one. Set the priority toHighfor no more than one variable in Initial Targets.
Plotting basic volt-ampere characteristics
You can plot the volt-ampere characteristics of a photodiode block without building a complete model. Use these graphs to study the effect of your chosen parameters on the performance of the unit.
If you parameterise the block Photodiode based on a data table, you can compare your plots to the data table to verify that you have parameterised the block correctly.
If you have a complete working model but are unsure which manufactured part to use, you can compare your graphs to the datasheets to help you decide.
To enable this option, uncheck the Enable thermal port parameter checkbox.
Assumptions and limitations
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If the Diode parameterization is set to
Use dark current plus a forward bias I-V curve data point, a voltage close to the diode turn-on voltage can be set. Typically, this value is in the range of 0.05 to 1 Volt. Usage of a value outside this region can result in poor evaluation . -
You may need to use non-zero values for the ohmic resistance and junction capacitance to avoid problems with numerical modelling, but the simulation may run faster if these values are zero.
Ports
Output
W is the density of light flux incident on the sensing element
scalar
Physical port related to the light flux incident on the photodiode.
Non-directional
+ - positive contact (anode)
electricity
The electrical port associated with the anode.
- - negative contact (cathode)
electricity
The electrical port associated with the cathode.
H is a thermal port
heat
Non-directional heat port.
Dependencies
To enable this port, select the Enable thermal port checkbox.
Parameters
Main
Enable thermal port - enable thermal port
` disabled (by default)` | enabled
When checked, the H thermal port is displayed, which allows the photodiode to be connected to the thermal network.
Sensitivity parameterization - sensitivity parameterization
Specify measured current for given flux density (by default) | Specify current per unit flux density.
Select one of the following sensitivity parameterization methods:
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Specify measured current for given flux density- specify the measured current and the corresponding flux density. This is the By default method. -
Specify current per unit flux density- specify the sensitivity of the device manually.
*Measured current - specify the measured current
25 uA (By default) | scalar.
The current that is used in the unit to calculate the sensitivity of the device.
Dependencies
This parameter is only visible if the Sensitivity parameterization parameter is set to Specify measured current for given flux density.
Flux density - luminous flux density
5 W/m^2 (by default) | scalar
The light flux density that is used to calculate the sensitivity of the device.
Dependencies
This parameter is only visible if the Sensitivity parameterization parameter is set to Specify measured current for given flux density.
Device sensitivity - device sensitivity
5e-06 m^2*A/W (by default) | scalar
Current per unit of light flux density.
Dependencies
This parameter is only visible when the Sensitivity parameterization parameter is set to Specify current per unit flux density.
Diode parameterization - diode parameterization
Use dark current plus a forward bias I-V data point (by default)| Use dark current and N
Select one of the following diode model parameterization methods:
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Use dark current plus a forward bias I-V data point- specify the current in the absence of light flux and a point on the volt-ampere curve of the diode. This is the By default method. -
Use dark current and N- Specify the no-light current and emission factor.
Current I1 - current at the forward bias point
0.1 A (By default) | scalar
Current at the forward bias point on the volt-ampere curve of the diode used in the block to calculate and .
Dependencies
This parameter is only visible if the Diode parameterization parameter is set to Use dark current plus a forward bias I-V data point.
Voltage V1 - forward bias I-V data point voltage
1.3 V (By default) | scalar.
The corresponding voltage at the forward bias point on the diode’s volt-ampere curve, which is used in the block to calculate and .
Dependencies
This parameter is only visible if the Diode parameterization parameter is set to Use dark current plus a forward bias I-V data point.
Dark current is the current in the absence of luminous flux
5e-9A (By default) | scalar.
Current through the diode when it is not exposed to light.
Emission coefficient, N - emission coefficient
3 (By default) | scalar.
Diode emission coefficient or ideality factor.
Dependencies
This parameter is only visible when the Diode parameterization is set to Use dark current and N.
Ohmic resistance, RS - series resistance of the diode
0.1 Ohm (by default) | scalar
Resistance connected in series with the diode.
Measurement temperature - measurement temperature
25 degC (by default) `scalar
The temperature at which the vol-ampere characteristic curve or current was measured in the absence of light flux.
Junction Capacitance
Parameterization - parameterization of junction capacitance
Fixed or zero junction capacitance (by default) | Use C-V curve data points | Use parameters CJ0, VJ, M & FC
Select one of the following options for modelling the junction capacitance:
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Fixed or zero junction capacitance- modelling the junction capacitance as a fixed value. -
Use C-V curve data points- Specify measurement data at three points of the diode C-V curve. -
Use parameters CJ0, VJ, M & FC- specify zero junction capacitance, junction contact potential difference, transition smoothness factor, and nonlinearity factor of the forward bias barrier capacitance.
Junction capacitance is the junction capacitance
60 pF (by default) | scalar.
Fixed value of junction capacitance.
Dependencies
This parameter is only visible if the Parameterization parameters are set to Fixed or zero junction capacitance.
Zero-bias junction capacitance, CJ0 - junction capacitance at zero bias
60 pF (by default) | scalar.
The value of the capacitance parallel to the exponential diode.
Dependencies
This parameter is only visible when the Parameterization parameter is set to Use parameters CJ0, VJ, M & FC.
Reverse bias voltages [VR1 VR2 VR3] - reverse bias voltages
[ 0.1 10 100 ] V (by default) | vector.
Vector of reverse bias voltage values at the three points of the diode’s C-V curve that the block uses to calculate , and .
Dependencies
This parameter is only visible if the Parameterization parameter is set to Use C-V curve data points.
Corresponding capacitances [C1 C2 C3] - capacitances corresponding to reverse bias voltages
[ 45 3 6 ] pF (by default) | vector.
Vector of capacitance values at the three points of the diode C-V curve that the block uses for calculation , and .
Dependencies
This parameter is only visible if the Parameterization parameter is set to Use C-V curve data points.
Junction potential, VJ - contact potential difference of the transition
1 V (by default) | scalar.
Contact potential difference of the transition.
Dependencies
This parameter is only visible if the Parameterization parameter is set to Use parameters CJ0, VJ, M & FC.
Grading coefficient, M - smooth transition coefficient
0.5 (By default) | scalar.
Smooth transition coefficient.
Dependencies
This parameter is visible only when Parameterization is set to Use parameters CJ0, VJ, M & FC.
Capacitance coefficient, FC - nonlinearity coefficient of the barrier capacitance of the forward biased junction
0.5 (by default) | scalar.
A coefficient that quantifies the decrease in discharge capacitance when a voltage is applied.
Dependencies
This parameter is only visible if the Parameterization parameter is set to Use C-V curve data points or Use parameters CJ0, VJ, M & FC.
Temperature Dependence
Parameterization - parameterization of temperature dependence
None - Use characteristics at parametr measurement temperature (by default) | Use an I-V data point at second measurement temperature | Specify saturation current at second measurement temperature | Specify the energy gap, EG
Select one of the following methods for parameterising the temperature dependence:
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None - Use characteristics at parametr measurement temperature- the temperature dependence is not modelled, or the model is calculated at the measurement temperature (as specified in the Measurement temperature parameters on the Main tab). This is the By default method. -
Use an I-V data point at second measurement temperature- when selected, you must specify the second measurement temperature , and the current and voltage values at that temperature. The model uses these values along with the parameters at the first measurement temperature to calculate the forbidden zone width value. -
Specify saturation current at second measurement temperature- when this value is selected, the temperature of the second measurement , and the saturation current value at this temperature must be specified. The model uses these values along with the parameters at the first measurement temperature to calculate the value of the forbidden band width. -
Specify the energy gap, EG- specify the forbidden zone width value manually.
Current I1 at second measurement temperature - current I1 at second measurement temperature
0.07 A (By default) | scalar.
Specify the value of diode current at voltage at second measurement temperature.
Dependencies
This parameter is only visible if the Parameterization parameters are set to Use an I-V data point at second measurement temperature.
Voltage V1 at second measurement temperature - V1 voltage at second measurement temperature
1.3 V (By default) | Scalar
Specify the voltage value on the diode at current at second measurement temperature.
Dependencies
This parameter is only visible if the Parameterization parameters are set to Use an I-V data point at second measurement temperature.
Second measurement temperature - saturation current, IS, at second measurement temperature
2.5e-7 A (By default) | scalar.
Specify the saturation current value at the second measurement temperature.
Dependencies
This parameter is only visible if the Parameterization parameters are set to Specify saturation current at second measurement temperature.
Second measurement temperature - second measurement temperature
125 degC (By default) | scalar.
Specify the value for the second measurement temperature.
Dependencies
This parameter is only visible if the Parameterization parameters are set to +Use an I-V data point at second measurement temperature or +Specify saturation current at second measurement temperature.
Energy gap parameterization - parameterization of the forbidden zone width
Use nominal value for silicon (EG=1.11eV) (by default) | Use nominal value for 4H-SiC silicon carbide (EG=3.23eV) | Use nominal value for 6H-SiC silicon carbide (EG=3.00eV) | Use nominal value for germanium (EG=0.67eV) | Use nominal value for gallium arsenide (EG=1.43eV) | Use nominal value for selenium (EG=1.74eV) | Use nominal value for Schottky barrier diodes (EG=0.69eV) | Specify a custom value
Select a value for the forbidden zone width from the list of predefined options or specify a custom value:
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Use nominal value for silicon (EG=1.11eV)is the value by default. -
Use nominal value for 4H-SiC silicon carbide (EG=3.23eV). -
Use nominal value for 6H-SiC silicon carbide (EG=3.00eV). -
Use nominal value for germanium (EG=0.67eV) -
Use nominal value for gallium arsenide (EG=1.43eV) -
Use nominal value for selenium (EG=1.74eV) -
Use nominal value for Schottky barrier diodes (EG=0.69eV) -
Specify a custom value- if you select this value, the Energy gap, EG parameters will appear in the dialogue box so that you can specify a custom value for .
Dependencies
This parameter is only visible if the Parameterization parameter is set to Specify the energy gap EG.
Energy gap, EG - width of the forbidden zone
1.11 eV (by default) | scalar.
Specify a custom value for the forbidden zone width, .
Dependencies
This parameter is only visible if the Energy gap parameterization is set to Specify a custom value.
Saturation current temperature exponent parameterization - parameterization of saturation current temperature exponent
Use nominal value for pn-junction diode (XTI=3) (By default) | Use nominal value for Schottky barrier diode (XTI=2) | Specify a custom value.
Select one of the following options to set the saturation current temperature value:
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Use nominal value for pn-junction diode (XTI=3)is the value by default. -
Use nominal value for Schottky barrier diode (XTI=2). -
Specify a custom value- if you select this value, the Saturation current temperature exponent, XTI parameters will appear in the dialogue box so that you can specify a custom value for .
Saturation current temperature exponent, XTI - saturation current temperature exponent
3 (By default) | scalar
Specify a custom value for the saturation current temperature exponent, .
Dependencies
This parameter is only visible if the Saturation current temperature exponent parameterization parameter is set to Specify a custom value.
Device simulation temperature - device simulation temperature
25 degC (By default) | Scalar
Specify the temperature value , at which the device will be simulated.
Initial Targets
Diode current
Priority - priority
None (by default) | Higt | Low
Current priority.
Value - current value
0 A (By default) | scalar
Current value.
The unit of measurement is A.