Diode

Symbol

Information

A diode is a semiconductor device that allows current to flow in one direction while blocking it in the reverse direction. It follows the Shockley diode equation, which defines its current-voltage relationship:

\[I = I_{ss} \cdot \left( e^{\frac{V}{n V_t}} - 1 \right)\]

Where:

• \(I\) is the current through the diode (Amperes)

• \(V\) is the voltage across the diode (Volts)

• \(I_{ss}\) is the saturation current, representing the small leakage current in reverse bias

• \(V_t\) is the thermal voltage, which depends on temperature

• \(n\) is the ideality factor, representing how closely the diode follows the ideal diode equation

Diodes are used in rectification, signal demodulation, voltage regulation, and circuit protection.

Ports

• p: Anode (positive terminal)

• n: Cathode (negative terminal)

Model

The Diode model implements a simple nonlinear diode.

A diode allows current to flow when forward biased and blocks it when reverse biased, following the Shockley equation.

Attributes:

• V (signal): Input voltage signal across the diode, defined between nodes (p, n).

• I (signal): Output current signal through the diode, defined between nodes (p, n).

• Iss (param): Saturation current (default: 1.0e-15 A).

• Vt (param): Thermal voltage (default: 0.025 V).

• n (param): Ideality factor (default: 1).

Methods:

analog(): Defines the diode behavior using the Shockley equation:

from pyams.lib import model, signal, param, voltage, current, explim

class Diode(model):
    """
    Simple diode model following the Shockley equation.
    """
    def __init__(self, p, n):
        # Signal declaration
        self.V = signal('in', voltage, p, n)
        self.I = signal('out', current, p, n)

        # Parameter declaration
        self.Iss = param(1.0e-15, 'A', 'Saturation current')
        self.Vt = param(0.025, 'V', 'Thermal voltage')
        self.n = param(1, ' ', 'The ideality factor')

    def analog(self):
        """Defines the diode’s current-voltage relationship"""
        self.I += self.Iss * (explim(self.V / (self.n * self.Vt)) - 1)

Command syntax

The syntax for defining a diode in a PyAMS simulation:

# Import the model
from pyams.models import Diode

# Dname: is the name of the diode instance
# p, n: The connection points in the circuit
Dname = Diode(p, n)