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Linearized Noise Figure
The AWR Design Environment supports linearized noise, which is the extraction of linear noise parameters from non-linear devices using only the linear simulation engine. Utilizing the linear simulator allows for real time computation of linear noise.
This example compares a nonlinear NEC HBT model to the NEC measured noise parameters for the same device. It also compares linearized noise to nonlinear noise.
The schematic "Linearized_Noise" shows the non-linear transistor, some bias components and voltage sources for the drain and the gate terminals of the HBT. The on-screen annotation verifies that the bias is set identical to that of the measured noise parameters (Ic = 5 mA, Vc = 2 V)
The measurements compare the linear optimum noise match (GMN) and the linear noise figure (NF) of the linear and nonlinear models.
Linearized vs Nonlinear_Noise
Linearized is a term that means that a nonlinear device model is evaluated at its bias point and then a linear model for the device is created. This means that the linear simulator can be used with the "linearized" version of the nonlinear model. Nonlinear means that the full nonlinear device equations are evaluated to get the circuit response.
This project has a schematic called "Nonlinear_Noise" that is setup to evaluate the full Nonlinear noise figure of this simple circuit. This simulation is not running since the graphs have the measurements for this schematic disabled. There are two differences in the schematic.
1. Port 1 is now a harmonic balance port where the input power level is specified. Currently the power level is low (-50 dBm) so that the device should be operating in a linear region.
2. The NLNOISE block is added. You can see the help for more details on all the settings of this block. The most critical setting on this block are the frequencies. These frequencies are always a frequency offset from the fundamental frequency of the circuit. So for circuits without conversion, one approach is to set the start and stop frequency to be a small offset number, like in this case.
Now you can enable the disabled measurements on the "Noise Figure" and "Gain" graphs and run the simulation. Notice how long the simulation takes compared to the linearized version. Also look at the results, they are identical to the linearized results. Now change the input power to -20 dBm and watch the gain and noise figure deviate from the linearized values. The device is no longer operating in a linear region.
Schematic - Linearized_Noise
Graph - Noise Match
Graph - Gain
Graph - Noise Figure