In Breadpad, users can adjust several parameters for transistors to fine-tune their SPICE simulations. Understanding these parameters is crucial for designing and analyzing electronic circuits accurately. Below is a detailed explanation of each parameter, including its expected units, value ranges, example values, and their impact on SPICE simulations.

## JFET Parameters (Junction Field-Effect Transistors)

### VTO (Threshold Voltage)

**Units**: Volts (V)**Expected Range**: Typically between -6V and 0V for N-channel JFETs and 0V to 6V for P-channel JFETs.**Example Value**: -2.0V for an N-channel JFET.**Impact**: VTO determines the gate-source voltage (Vgs) at which the JFET begins to conduct. Modifying VTO in simulations allows users to explore how different threshold voltages affect the device's operation, particularly the transition between cutoff and saturation regions.

### BETA (Transconductance Parameter)

**Units**: Amperes per Volt Squared (A/V^2)**Expected Range**: Varies widely depending on the JFET but is generally in the range of 1.0e-4 to 1.0e-2 A/V^2.**Example Value**: 1.0e-3 A/V^2 for a typical JFET.**Impact**: BETA affects the slope of the ID-VGS curve in the ohmic region, essentially determining how effectively the JFET can amplify a signal. Adjusting BETA helps simulate JFETs with different amplification capabilities.

### LAMBDA (Channel-length Modulation Parameter)

**Units**: Per Volt (/V)**Expected Range**: 0 to 0.02 /V.**Example Value**: 1.0e-4 /V.**Impact**: LAMBDA models the variation of drain current (ID) with drain-source voltage (VDS) due to the channel-length modulation effect. It influences the output characteristics, particularly in the saturation region, simulating how ID changes as VDS increases.

### RD (Drain Ohmic Resistance)

**Units**: Ohms (Ω)**Expected Range**: 0 to a few hundred Ohms.**Example Value**: 100Ω.**Impact**: RD represents the resistance in the path between the drain and the channel. It impacts the voltage drop across the drain terminal and the total output resistance of the JFET, affecting the output characteristics.

### RS (Source Ohmic Resistance)

**Units**: Ohms (Ω)**Expected Range**: 0 to a few hundred Ohms.**Example Value**: 100Ω.**Impact**: Similar to RD, RS affects the voltage drop across the source terminal and influences the overall gain and output impedance of the JFET.

### CGS (Zero-bias G-S Junction Capacitance)

**Units**: Farads (F)**Expected Range**: Picofarads (pF) to nanofarads (nF).**Example Value**: 5pF.**Impact**: CGS affects the frequency response of the JFET, particularly its input capacitance and thus its bandwidth. Higher values can lead to slower response times.

### CGD (Zero-bias G-D Junction Capacitance)

**Units**: Farads (F)**Expected Range**: Picofarads (pF) to nanofarads (nF).**Example Value**: 1pF.**Impact**: CGD influences the Miller effect, which can significantly affect the voltage gain and bandwidth of amplifiers using JFETs.

### PB (Gate Junction Potential)

**Units**: Volts (V)**Expected Range**: 0.5V to 1V for typical JFETs.**Example Value**: 0.6V.**Impact**: PB affects the gate-source and gate-drain diode characteristics, particularly their reverse-bias behavior, which is important for understanding leakage currents and breakdown voltages.

### IS (Gate Saturation Current)

**Units**: Amperes (A)**Expected Range**: Very small, typically in the range of 1.0e-14 to 1.0e-16 A.**Example Value**: 1.0e-14 A.**Impact**: IS impacts the off-state leakage current through the gate, which is critical for low-power applications and determining the off-state device behavior.

### B (Doping Tail Parameter)

**Units**: Dimensionless**Expected Range**: 1 and above.**Example Value**: 1.1.**Impact**: This parameter models the doping profile of the JFET's channel. A higher value suggests a more abrupt transition from the channel to the doped regions, which can affect the device's turn-on characteristics and channel resistance. It is useful for simulating devices with non-uniform doping profiles.

### KF (Flicker Noise Coefficient)

**Units**: Dimensionless**Expected Range**: Typically very small or zero.**Example Value**: 0 (for simplicity in basic simulations).**Impact**: KF represents the coefficient for 1/f noise or flicker noise in the JFET. This type of noise is significant in low-frequency applications. By adjusting KF, users can explore how flicker noise impacts the low-frequency performance of amplifiers or oscillators.

### AF (Flicker Noise Exponent)

**Units**: Dimensionless**Expected Range**: Usually close to 1.**Example Value**: 1 (common default).**Impact**: AF modifies the frequency dependency of the flicker noise, affecting how noise power density changes with frequency. This parameter is crucial for noise analysis in audio and other low-frequency applications.

### NLEV (Noise Equation Selector)

**Units**: Dimensionless**Expected Range**: 1, 2, 3, etc., depending on the model.**Example Value**: 3 (for advanced noise modeling).**Impact**: NLEV selects the noise model used in simulations, allowing users to choose between different methods of noise analysis. This flexibility is valuable for accurate noise performance predictions in sensitive applications.

### GDSNOI (Channel Noise Coefficient for NLEV=3)

**Units**: Dimensionless**Expected Range**: 1 and above.**Example Value**: 2.0.**Impact**: GDSNOI is relevant when using advanced noise models (e.g., NLEV=3), affecting the simulated channel noise. It allows for detailed noise modeling, particularly in high-frequency or precision applications.

### FC (Forward-bias Depletion Capacitance Coefficient)

**Units**: Dimensionless**Expected Range**: 0 to 1.**Example Value**: 0.5 (typical).**Impact**: FC modifies the voltage dependency of the junction capacitances (CGS and CGD), particularly under forward bias conditions. This affects the charging behavior of the gate junctions, influencing AC performance and transient response.

### TNOM (Parameter Measurement Temperature)

**Units**: Degrees Celsius (°C)**Expected Range**: Typical lab conditions, e.g., 25°C.**Example Value**: 27°C.**Impact**: TNOM specifies the temperature at which the JFET parameters were measured. This is the reference point for temperature-dependent simulations, crucial for accurately modeling device behavior over a range of operating temperatures.

### TCV (Threshold Voltage Temperature Coefficient)

**Units**: Per Degree Celsius (/°C)**Expected Range**: Small, typically around 0.01 to -0.01 /°C.**Example Value**: 0.01 /°C.**Impact**: TCV models how the threshold voltage changes with temperature. This is important for designing circuits that operate reliably over a wide temperature range, as it affects the turn-on characteristics of the JFET.

### VTOTC (Alternative Model Threshold Voltage Temperature Coefficient)

**Units**: Per Degree Celsius (/°C)**Expected Range**: Similar to TCV but used in alternative models.**Example Value**: -2.5m /°C.**Impact**: Like TCV, VTOTC allows for temperature-dependent threshold voltage modeling in alternative JFET models. It offers additional flexibility in simulating temperature effects.

### BEX (Mobility Temperature Exponent)

**Units**: Dimensionless**Expected Range**: 0 to 2.**Example Value**: 1.1.**Impact**: BEX models the temperature dependency of the carrier mobility. This affects the JFET's transconductance and saturation current over temperature, critical for thermal performance analysis.

### BETATCE (Mobility Temperature Exponent for Alternative Model)

**Units**: Percent per Degree Celsius (%/°C)**Expected Range**: Typically negative values.**Example Value**: -0.5.**Impact**: BETATCE is another parameter for modeling the temperature dependency of carrier mobility, used in alternative models. It helps simulate how the device's gain changes with temperature.

### XTI (Gate Saturation Current Temperature Coefficient)

**Units**: Dimensionless**Expected Range**: 2 to 4, typical for semiconductor junctions.**Example Value**: 3.0.**Impact**: XTI affects how the gate saturation current varies with temperature, which is vital for predicting leakage currents and power dissipation in different thermal conditions.

### EG (Bandgap Voltage)

**Units**: Volts (V)**Expected Range**: Around 1.11V for silicon devices.**Example Value**: 1.11V.**Impact**: EG specifies the semiconductor material's bandgap energy, impacting various temperature-dependent behaviors, including saturation current and threshold voltage shifts.

## BJT (Bipolar Junction Transistor)

### SUBS (Substrate Connection)

**Unit:**Dimensionless**Range:**{1, -1}**Example:**`1`

for vertical geometry,`-1`

for lateral geometry.**Impact:**Determines the geometry of the transistor, affecting its electrical properties and how it interacts with the substrate.

### IS (Transport Saturation Current)

**Unit:**Ampere (A)**Range:**Typically in the range of 1.0e−161.0e−16 to 1.0e−121.0e−12 A.**Example:**`1.0e-16`

A for small signal transistors,`1.0e-15`

A for power transistors.**Impact:**Influences the transistor's active region characteristics. A key parameter for determining the DC current gain.

### IBE, IBC (Base-Emitter and Base-Collector Saturation Current)

**Unit:**Ampere (A)**Range:**Usually very small, similar to IS.**Example:**`1.0e-16`

A.**Impact:**These parameters affect the leakage currents in the transistor, impacting the off-state behavior and reverse-bias characteristics.

### ISS (Reverse Saturation Current)

**Unit:**Ampere (A)**Example:**`1.0e-15`

A.**Impact:**Determines the substrate leakage current, significant for vertical devices.

### BF (Ideal Maximum Forward Beta)

**Unit:**Dimensionless**Range:**Typically 50 - 300 for small signal transistors, higher for power transistors.**Example:**`100`

.**Impact:**Directly influences the transistor's current gain in the forward-active mode.

### NF (Forward Current Emission Coefficient)

**Unit:**Dimensionless**Range:**Close to 1, usually between 1 and 2.**Example:**`1.0`

.**Impact:**Affects the linearity and efficiency of the transistor, influencing the forward current gain.

### VA, VAF (Forward Early Voltage)

**Unit:**Volt (V)**Range:**Can be very high (tens to hundreds of volts) or infinity.**Example:**`200`

V.**Impact:**Indicates the voltage dependence of the transistor's base width, impacting high-voltage behavior and gain.

### IKF (Corner for Forward Beta Current Roll-Off)

**Unit:**Ampere (A)**Range:**Depends on the transistor type; higher for power transistors.**Example:**`0.01`

A.**Impact:**Determines the point at which the current gain starts to decrease with increasing collector current.

### NE, NC (Emission Coefficients)

**Unit:**Dimensionless**Range:**Typically around 1.5 to 2.**Example:**`1.5`

for NE,`2`

for NC.**Impact:**Affects the base-emitter and base-collector junctions' I-V characteristics, important for modeling non-ideal behaviors.

### RB, RE, RC (Base, Emitter, Collector Resistances)

**Unit:**Ohm (Ω)**Range:**Varies widely based on transistor design and application.**Example:**`100`

Ω for RB,`1`

Ω for RE,`10`

Ω for RC.**Impact:**Represents the internal resistances of the transistor, affecting the voltage drops and power dissipation.

### CJE, CJC, CJS (Junction Capacitances)

**Unit:**Farad (F), typically in pF.**Range:**Varies with transistor size and design; smaller for high-frequency transistors.**Example:**`2pF`

for both CJE and CJC.**Impact:**Critical for high-frequency operation, affecting the speed of the transistor by introducing charging and discharging times.

### VJE, VJC, VJS (Built-in Potentials)

**Unit:**Volt (V)**Range:**Typically around 0.6 to 0.7 V for silicon transistors.**Example:**`0.6`

V for VJE,`0.5`

V for VJC.**Impact:**Determines the turn-on characteristics of the junctions, essential for accurate threshold voltage modeling.

### MJE, MJC, MJS (Junction Exponential Factors)

**Unit:**Dimensionless**Range:**Typically around 0.33 to 0.5.**Example:**`0.33`

for MJE,`0.5`

for MJC.**Impact:**Affects the voltage dependence of the junction capacitances, impacting the transistor's frequency response.

### TF, TR (Transit Times)

**Unit:**Second (sec), typically in ns or ps.**Range:**Varies with the speed of the transistor; shorter for faster devices.**Example:**`0.1ns`

for TF.**Impact:**Directly affects the switching speed of the transistor, crucial for digital and high-frequency applications.

### Temperature Parameters (TNOM, TREF, etc.)

**Unit:**°C for temperature, dimensionless or /°C for coefficients.**Example:**`27`

°C for TNOM.**Impact:**These parameters adjust the model to simulate the temperature dependence of the transistor's behavior, critical for thermal stability and performance analysis.