## Define Device Noise Using Linear Circuit Wizard

You can use the Linear Circuit Wizard block to generate device noise and model the response of a linear circuit. The device noise generators are built inside the MATLAB System block that the Linear Circuit Wizard configures, and include flicker noise as well as uniformly distributed Gaussian noise.

**Note**

The Linear Circuit Wizard also offers a **Device
noise source** type of input port through which you can inject your own model
of device noise. For any given device, you should use either a **Device noise source** input port or an internal device noise generator, but
not both.

### Device List

The device noise generators are designed to model the current noise produced by
resistors and semiconductor devices such as MOSFETs. In the **Device
Noise Generators** tab of the Linear Circuit Wizard, you can
select from a list of resistors and controlled current sources, which are the circuit
elements for which device noise can be modeled. To model a source of device noise, choose
the circuit element from the list, enable its device noise generator, and set the parameters
for that device noise generator. To disable a device noise generator, select the circuit
element and disable its device noise generator.

### Device Noise Specification

You can configure a device noise generator using three parameters: **Noise coefficient**, **Corner frequency**, and
**Independent noise source/Noise generator seed**.

#### Noise Coefficient

The **Noise coefficient** parameter defines the spectral
density of the generated noise through the equation

*i*^{2} =
4*k**T**G*

where *i*^{2} is the noise spectral density
in A^{2}/Hz, *k* is Boltzmann’s constant,
*T* is the temperature in degrees Kelvin, and
*G*^{2} is the noise coefficient in units of
conductance (Siemens or 1/Ohms).

For resistors, the device noise is Johnson/Nyquist noise, and the noise coefficient is *G* = 1/*R*, where *R* is the conductance of the resistor. The
Linear Circuit Wizard performs this calculation from the resistor value
in the netlist and sets the noise coefficient to the resulting conductance.

For MOSFETs, the noise coefficient is *G* =
*γ**g*_{dso}, where *γ* has a lower bound of 2/3 for MOSFETs with
relatively long channel length, and can be 1.5 or greater for short channel MOSFETs.
*g*_{dso} is the output conductance at zero drain
bias. Because *γ* is process dependent, you must perform this calculation
and enter the resulting noise coefficient.

#### Corner Frequency

The **Corner frequency** parameter defines the flicker
noise for the device. Flicker noise spectral density increases as approximately 1/f. The
corner frequency is the frequency at which the flicker noise is approximately equal to the
spectral density of the uniformly distributed thermal noise. The corner frequency is
process dependent, but typically has a value around 1 kHz.

Within the MATLAB System block configured by the Linear Circuit
Wizard, the frequency response of the flicker noise is implemented by a filter
which accurately creates the 1/*f* spectral density from the corner frequency to four decades below the
corner frequency. At even lower frequencies, the modeled flicker noise is essentially
constant.

#### Independent Noise Source/Noise Generator Seed

While most sources of device noise are statistically independent of each other, there
are cases in which the same noise process is affects the outputs of multiple devices. For
the most common case, enable **Independent noise source**.
However, when multiple devices must be driven by the same stochastic process, disable
**Independent noise source** on the device noise generator
for each of those devices and set **Noise generator seed** to
the same positive integer. The resulting device noise generators share the same stochastic
process but are statistically independent of all other device noise generators.