This document provides information on modeling and parameter extraction for diodes. It discusses: 1. Diode specification sheets include key parameters like forward voltage, maximum current, reverse saturation current, and temperature range. 2. Diode models include large signal DC and small-signal AC models. The DC model uses parameters like saturation current, series resistance, and emission coefficient. The AC model includes junction capacitance and dynamic conductance. 3. Methods are described to extract model parameters from diode data sheets and measurements of I-V and C-V characteristics. Parameters like saturation current, series resistance, and junction capacitance can be determined through curve fitting and other calculations.

1. Data sheet and circuit models
of diode
1

2. Diode Specification Sheets
Data about a diode is presented uniformly for many different diodes. This
makes cross-matching of diodes for replacement or design easier. It
includes:
1. Forward Voltage (VF ) at a specified current and temperature
2. Maximum forward current (IF) at a specified temperature
3. Reverse saturation current (IR ) at a specified voltage and
temperature
4. Reverse voltage rating, PIV or PRV or V(BR), at a specified
temperature
2

3. 5. Maximum power dissipation at a specified temperature
6. Capacitance levels
7. Reverse recovery time, trr
8. Operating temperature range
Forward Bias Voltage
The point at which the diode changes from no-bias condition to forward-
bias condition occurs when the electrons and holes are given sufficient
energy to cross the p-n junction. This energy comes from the external
voltage applied across the diode.
3

4.  The forward bias voltage required for a:
• gallium arsenide diode 1.2 V
• silicon diode 0.7 V
• germanium diode 0.3 V
Peak forward current, IFRM
The maximum forward current with sine-wave operation, f ≥ 25 Hz, or
pulse operation, f ≥25 Hz, having a duty cycle tp/T ≤ 0.5.
Reverse current, IR (leakage current)
The current which flows when reverse bias is applied to a semiconductor
junction. 4

5. Temperature Effects
As temperature increases it adds energy to the diode.
• It reduces the required forward bias voltage for forward-bias
conduction.
• It increases the amount of reverse current in the reverse-bias condition.
Breakdown voltage, VBR Reverse voltage at which a small increase in
voltage results in a sharp rise of reverse current. It is given in the technical
data sheet for a specified current.
Breakdown voltage
5

6. • It increases maximum reverse bias avalanche voltage. Germanium
diodes are more sensitive to temperature variations than silicon or
gallium arsenide diodes
Resistance Levels
Semiconductors react differently to DC and AC currents. There are three
types of resistance:
• DC (static) resistance
• AC (dynamic) resistance
• Average AC resistance 6

7. 7

8. 8

9. 9

10. Diode Capacitance
10

11. 11

12. 12

13. Diode Model Parameters
13

14. 14

15. Large Signal DC Model
• Characterized by the R/s between dc current and voltage at diode
terminals
• Parameters used to model are Is , Rs , N, BV, and IBV.
Is – reverse saturation current
Rs - Ohmic resistance of metal contacts and neutral region of
diode
N – emission coefficient to modify I-V characterstics of diode
BV and IBV – model reverse breakdown behavior 15

16. Figure 3.1 shows the equivalent circuit of diode for large signal analysis.
16

17. Where
 D1 – intenal diode
 Rs – series resistance
 Gmin – shunt conductance (10-12 mho or can be set to any non-zero
value)
• Hence dc-model variables are:
 VF –voltage across external diode terminals
 VD – voltage across internal terminals
 ID – terminal current 17

18. • With these parameters and variables the large signal dc
characteristics can be modeled by the following equations:
• Four regions of operation describe functional relationship between
internal diode voltage and terminal current as :
18

19. • For all above equations Vt is thermal voltage given by:
19

20. • To insure convergence between regions (c) and (d), it is necessary
that IBV is:
20

21. 21

22. Small –signal AC- model of diode
• Derived from the linearized small-signal behavior of internal diode
i.e :
22

23. Where
CJ – junction capacitance
GD – dynamic conductance
CD – diffusion capacitance
With all are bias dependent.
• Junction capacitance (CJ) can be modeled by parameters CJO, VJ,
M and FC.
• CJO and VJ are identical to zero-bias junction capacitance Cj (0) and
contact potential Vj of ideal diode.
23

24. • M – grading exponent used to change the slope of junction
capacitance vs reverse voltage (abrapt junction diode M=0.5 but for
graded junction M=0.333).
• FC – parameter to model the capacitance under forward bias
condition.
 Variables for the model CJ in Farad and internal diode voltage VD
are related as:
24

25.  To insure equation 3.11 well behaved, FC is restricted as:
25

26. • A typical C –V curve produced by above equations is given as:
26

27.  The variable dynamic conductance GD is a function of internal
diode voltage VD and given in three region of operations as:
27

28.  The variable diffusion capacitance CD modeled by forward
transient time parameter TT and the parameters Is and N in three
region of operations as:
28

29. Note
 Above model parameters of diode have certain limitations. For
some of the parameters, suggested value restrictions are given in
order to insure convergence.
29

30. 30

31. Parameter Extraction
1- Forward DC characteristics
• Is , Rs and N are parameters to model dc characteristics (large signal model)
in the forward region.
• There are three methods to extract
I. Three point I-V method
II. Method which uses fixed value of Rs (taken from method I)and
perform linear regression data fit over the I-V curve to extract Is and
N.
III. Use fixed value of Is and perform a non-linear data fit to extract N
and Rs .(Useful if IR reverse leakage current is specified). 31

32. Method I
 Use forward-bias I-V curve where current axis is logarithmic
Step-1: Select three data points from the I-V curve as points 1, 2 and 3
Step-2: Calculate values for Rs , N and Is using equations:
32

33. 33

34. 34

35. Method II (Linear regression with fixed Rs)
Step-1 : Select a value of Rs from method 1
Step-2 : Perform linear regression data fit on n data points taken from
I-V curve, equation 3.42. where yi and xi calculated from equation
3.43 and 3.44. Then values for b and m.
Step-3 : Calculate values of Is and N from equation 3.48 and 3.49
respectively.
35

36. • Consider an equation which represent the diode dc characteristics:
Where IDi and VFi represent ith data point on I-V curve of diode.
• Assume exponential term in equation 3.39 is sufficiently large this
equation will be modified as:
• Taking natural logarithm both side of equation 3.40 then
36

37. 37

38. • Values for b and m can be found by solving the matrix equation 3.47:
Then Is and N determined by:
38

39. 39
Extraction of junction capacitance parameters
from C-V curve
There are two methods:
I. Method I : (Three point C-V method) – use the reverse bias plot of
junction capacitance verses reverse bias voltage.
Procedures:
Step 1 : select a data point at the lower end of the C-V curve where voltage
less than ideal VJ (that is 0.8 to 1 v)
Step 2 : select two data points at the upper end of C-V curve (as shown on the
graph by 2 and 3). Voltages should be much greater than ideal VJ .

40. 40
Step 3 : Calculate the values of M, VJ , CJO and FC as:

41. 41

42. 42
II, Method II : (Linear regression with fixed VJ) – perform linear data
regression data fit for the whole data point of C-V curve. Consider the relation
between junction capacitance and reverse voltage:
Take natural logarithm to equation 3.65 both sides:

43. 43
Values for b and m can be found by solving the matrix equation 3.47:

44. 44
The parameters CJO and M are calculated as:
Procedure
Step 1 : Select value VJ which may be value calculated from method I.
Step 2 : Perform linear regression data fit on n data points taken from the
C-V curve to determine b and m.
Step 3 : Calculate the values of CJO and M from equation 3.72 and 3.73
respectively and value of FC from equation 3.64.

45. 45
Steps for extracting the parameter TT are:
Step 1 : From the device data sheet, determine values for the reverse recovery
time trr , the forward-bias diode current IF and the slew-rate of the current
waveform di/dt .
Step 2 : Generate a function of the forward transient time TT where:
Step 3 : Use Newton’s method to solve equation 3.79 for the value of TT that
will set f(TT) equals to zero.

46. 46
Reverse breakdown characteristics
Steps for extracting the parameters BV and IBV are:
Step 1 : From the diode data sheet, determine the value of the maximum DC
blocking voltage VR (max)
Step 2 : Multiplying the above voltage by a constant kBV (having value ranging
from 1.3 to 2) to produce breakdown voltage of:
BV = kBV * VR (max)
Step 3 : Calculate the value of IBV as:

47. 47
Temperature characteristics are reading assignments

48. 48