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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.


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

i2 = 4kTG

where i2 is the noise spectral density in A2/Hz, k is Boltzmann’s constant, T is the temperature in degrees Kelvin, and G2 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 = γgdso, 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. gdso 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.

See Also

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