Microwave Office Training - University of Colorado Boulderecee.colorado.edu/~ecen4634/3_Linear_Simulation.pdf · 1 Microwave Office Training Linear Simulation –Low Noise Amplifier

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Microwave Office Training

Linear Simulation – Low Noise Amplifier

2 Linear Simulation

Summary

• Linear Simulation

– S parameters at Ports - and derived parameters ... Gain, NF

• Low Noise Amplifier as an Example to show:

– Creating schematics

– Data libraries

– Editing schematic symbols (adding explicit ground nodes)

– Creating graphs and adding measurements

– Measurements: S parameters, Noise, Gain

– Tuning Parameters

• Step Response (Optional)

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3 Linear Simulation

Linear Simulation

• Linear Simulation solves for S parameters in the frequency domain at ports.– Internally, it solves the Y matrix.

• It is an ideal choice for:– Linear Amplifier Analysis

– Linear Noise Analysis

– Interconnect / Passive elements

• It Cannot:– Show currents and voltages at nodes. (Use linear HB)

– Show time domain transients and start up conditions.

• It Can:– Show step/pulse response for passive circuits.

– Work with biased devices - if they have a model, not just S parameter data. (For example - Gummel Poon)

4 Linear Simulation

Example - A Low Noise Amplifier

• Design Goals of a 5 GHz amplifier are:

– Gain > 10 dB.

– Noise Figure < 1.15 (1.2 in dB)

• We will learn:

– Insert S parameter file for a transistor.

– Add graphs and measurements to look at:

• S parameters

• Noise figures - NF and NFmin

• Stability figures: K, B1

– Smith Chart Graphs and Circle Measurements

• Stability Circles, Gain Circles, Noise Figure Circles

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5 Linear Simulation

Example - A Low Noise Amplifier -2

Step 1: Create a Schematic “ Device” in a new project

Step 2: Import the S parameter data set for the HEMT transistor - FHX35LG.s2p

Tip: Make sure you’re looking for Touchstone files -

or you might not see the file in the directory.

6 Linear Simulation


Step 3: Look at the S parameter for the device.

double click on the data file - to see the S parameters and the the

Noise data.

The S parameters are

from 100 MHz to 20

GHz

The noise data are

from 2 to 18 GHz.

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7 Linear Simulation


Step 4: Insert the data set as a sub-circuit into the schematic “Device”.

Note: You can insert a sub-circuit

by:

•Draw - Insert Sub-circuit

•Hotkey is: Ctrl K

•Subcircuits in Elements Library

Tip: Make sure you select Explicit Ground

Node. This is used for transistor S

parameter data - so you expose the 3rd port

(Usu. the source in common source.) For

interconnect S parameter data - use

Normal.

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Step 5: Change the Symbol to a FET.

It looks more like a transistor and is less confusing which port is which.

Select the Sub-Circuit’s

Properties

Right Click (RC)

Select the FET symbol

Tip: Make sure the port numbers of the symbol - match what you expect.

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9 Linear Simulation


Step 6: Complete the amplifier by attaching ports.

Tip: Useful Hot Keys:

•Add a port: Ctrl P

•Add a ground: Ctrl G

You can rotate, flip, and mirror the port before placing it.

•To rotate - right click (RC)

•To Flip About the Horizontal Axis - Shift RC.

•To Flip About the Vertical Axis - Alt Shift RC.

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Step 7: Set the simulation frequencies from 0.1 to 20 GHz - in steps of 0.1 GHz.

Select Project Options

A very common error is to forget the Apply Button.

Note: This sets the

frequencies for all project

simulations - unless you

override them. You can do

so at the individual circuit

level, or EM simulation

level.

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Step 8: Create the Graphs and Measurements

Create a Graph called Input Port

Create a Measurement - S11

Measurement

Added to the Graph



Add a measurement S22 to the same Graph.

Data source name

Various Control

Fields

We are sweeping the x - axis

with Frequency

This is a linear measurement.

Measurements in MWO are carried

out in the Graphs.

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Step 9: Run the simulator.Three ways to do this:

•Lightning Bolt in the Toolbar

•Simulate > Analyze

•F8

You will get a warning

message. It’s saying you

don’t have any noise data

at 20 GHz - so it’s

extrapolating.

Standard Toolbar



Tip: You can RC on the graph - and bring up properties.

There you can change the Graph’s appearance: traces, axes, fonts, etc.

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Step 10: Change the graph to a Smith Chart.

RC on the Graph in the Browser



Step 11: Add a graph - “Two Port Gain”.

-Add measurement: S21 (Measurement type Linear > Port Parameters)

-Add measurement: Maximum Stable Gain (MSG) (Measurement Type -

Linear > Gain)

Maximum Stable Gain is in dB.

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Step 12: Make the Graph Look Nicer.

RC on the Graph > Properties

Change the x axis limits to 0 to 20 GHz.

We will use the left axis for S21 and the right axis for MSG.



Setting the MSG to the right axis.

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Tip - Interpolation between data

points

The wiggle in the S21 curve

is because we are using

linear interpolation.

This can be changed in Project Options

> Interpolation.Change it to Spline or Rational

It’s Smoother!



Step 13: Make a Graph “ Two Port Noise Parameters”

-Add measurements for Noise Figure (NF) and Noise Figure Minimum (NFmin)

(The measurement type is Noise.)

- Make the graph nice by resetting the lower frequency to 0.

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Step 14: Create a graph “Stability Data”

- Add measurements for K and B1. (Measurement type is -linear.)

Note: Don’t use dB.



Step 15: Add a marker to the trace for K.

RC on the graph and select

Add Marker ( Ctrl M).

Select the K trace and add the marker.

RC on the marker and select search - for 1.

Remember K < 1 and/or B1 < 0 is unstable.

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Step 16: Stabilize the amplifier by adding resistance.

Copy the schematic and rename the copy “Stable Device”.

Tip: The easiest way to do this is drag Device into Circuit Schematics

- and Copy of Device will be created.

This line takes out the resistor R3 at 5

GHz.

Stable Device


Stable Device

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Step 17: Update the graphs with the new Stable Device S parameters, Gain, Nose, and Stability measurements.

Tip: A quick way to do this - is any measurement can be dragged on top of the

graph in the browser - creating a copy. Then open it, and change the Data

Source Name to Stable Device.

K and B1

K > 1 and B1 > 0

Note: Autoscaling is

turned off for the left

axis, as K gets very

large near DC.



S11 and S22

S22 has gotten smaller

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The Gain is lower - as expected.



Step 18: Stability Circles

Create a graph - Smith Chart type, named “Stability Circles”

-Add the measurement: SCIR1 (Measurement Type - Circle).

-Use the Source Name “ Device”. (It’s more interesting - not stable.)

A circle has been added for

each frequency.

Unstable regions.

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What if I want only a few circles?

Method 1: Have fewer frequencies.

- You can do this in Options at the Project level or the circuit level.

Method 2: In the “Device” Schematic - insert a SWPFREQ block.

- For values: stepped(1.0e9,10.0e9,1e9) - 1 to 10 GHz in 1 GHz increments

In the measurement dialog box

- Change the Sweep Freq to

SWPFRQ.FWP1

Now we can use these frequencies - instead of all the project frequencies.

Click the arrow to select FSWP1.

Optional

Located under Simulation Control.



Fewer Circles - Much Easier to Read.

Tip: The dotted side of the circles is the unstable region.

Optional

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Method 3: Create a dummy sweep variable.

Circle measurements require a swept variable - which by default is frequency.

Idea: Create a dummy sweep variable - and sweep on that - in effect disabling

the sweep.

Insert the SWPVAR into the

schematic “device” and create a

variable “foo”.

Create an equation for “foo”.

To insert an equation - Ctrl E or

Draw > Insert Equation

Optional

Located under Simulation Control.



Change the measurement settings

The swept variable

foo is set to the x

axis. (So - we are

using a dummy for

the x axis sweep.)

The frequency is

selected by the

tuner.

Optional

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The Tuner

You can now use the tuner to shift through

frequencies and stability circles.

Optional Equations Toolbar



Step 19: Add a graph called “Noise and Gain Circles”. We will work with the Stable Device data.

Set the Project Frequency to

1 point - 5 GHz. This is where we want to tune.

Add NFCIR (Linear > Circle) with 2 circles and 0.5 dB steps.

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Add GAC_MAX - Available Gain (Linear > Circle)

with a Gain step 1 and 2 circles.



Let’s make a matching input circuit.

Step 20: Create a schematic “Input Matching Circuit”

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Step 21: Create a schematic - “Amp”

- Include Stable Device and Input Matching Circuit as subcircuits.

Amp Schematic



Window in Window Technology

Allows you to “see” other circuits, and graphs in your schematic.

Open up “Amp”.

LC on Stable Device in the browser and drag it into the schematic.

Drag - to create the area. You see the window Stable

Device.

Optional

Looks Pretty!

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Step 22: Tune the L’s to get a good compromise between Gain and NF.

In “Input Matching” select L1 and L2 for tuning.

-Method 1: Use the tuning tool. Select each of them.

-Method 2: Select Properties for each of them.

Equations Toolbar

Set to tune 0 to 10 nH.

When selected for tuning - the parameters

turn blue.



Step 23: Tune the L’s to get a reasonable compromise between NF and Gain.

- Add S22 of Input matching to the graph Noise and gain Circles.

Tuner Tune until there is a

reasonable compromise

between Gain and Noise

Figure.

S22 of your input

matching will equal S11

of your stable device.

Equations Toolbar

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Step 24: Add an “Output Matching Circuit”.

Optional

Tune the values to get maximum gain.

Note: We have not used simultaneous, conjugate match

designs - so the output circuit will influence the design

of the input circuit.

You can add - S21 of the Amp to

the Two Port Gain for example,

and tune over the C and L’s.



Step 25: Set the simulation frequencies back to 1 to 20 GHz and look at the Gain and NF.

Optional

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Example - Step Response

Step 1: Make a new schematic - “Test Loads”.

Step Response to the input of the device

These are some test loads for us to try to make sure we understand step

response.

Optional


Example - Step Response - 2

Step 2: Make a graph - “Step Response”

Add step response measurements: (Linear > TDR) TDR_LPS.

- Try S11, S22, and S33 of Test Loads.

Select Real

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The results are the same as a Time Domain Reflectometer.

A short circuit

A 100 Ohm Load

Tip: Linear analysis can do this because it’s taking the

FFT of the S parameters.

An RC circuit.



Step 3: Add the Step Response of the “Device”. Convince yourself it looks like an RC curve.

Documents

Microwave Office Training - University of Colorado Boulderecee.colorado.edu/~ecen4634/3_Linear_Simulation.pdf · 1 Microwave Office Training Linear Simulation –Low Noise Amplifier