The Active CirculatorThe Active Circulator

Insertion

Vtr

Isolation

Vant

Vrx

Specs

Insertion Loss < -.5dB

Isolation > -15db

Frequency > 30 MHz

10W < Power < 50W

3 NPN Circulator3 NPN CirculatorSmall Signal DiagramSmall Signal Diagram

Purpose: Design a CCW Purpose: Design a CCW

circulator out of a 3-port, circulator out of a 3-port,

3-transitor network.3-transitor network.

Design: Construct Design: Construct

h-parameter admittanceh-parameter admittance

matrix. Then find transistormatrix. Then find transistor

parameters that make it parameters that make it

behave like a circulator.behave like a circulator.

Tanaka-Lee SchematicTanaka-Lee Schematic

Experiment ResultsExperiment ResultsOperating Points: VOperating Points: Vtrs trs = 100mV, f = 1kHz= 100mV, f = 1kHz

Results: Isolation = -19.33dB, Insertion Loss = -1.012dB Results: Isolation = -19.33dB, Insertion Loss = -1.012dB

Power = 1.13mWPower = 1.13mW

SimulationSimulation

ConsiderationsConsiderations

Cons:Cons:

Bias CurrentBias Current

VVbebe Overdrive Overdrive

RRpipi Sensitivity Sensitivity

Pros:Pros:

High FrequencyHigh Frequency

Parameters Easily CalculatedParameters Easily Calculated

Symmetric Symmetric

Basic ModelBasic ModelPurpose: A more “flexible” op-ampPurpose: A more “flexible” op-amp

Design Specs:Design Specs:

V1=V2=7.5VV1=V2=7.5V

V3=-0.8VV3=-0.8V

IR1=IR2=1mAIR1=IR2=1mA

3-Port Scheme 3-Port Scheme

Idea from the topology in the proposalIdea from the topology in the proposal

Continued: Simulation ResultContinued: Simulation Result

Insertion Loss: -1.41DB

Need simplification for analysis purpose.

Simplified TopologySimplified Topology

Continued-Simulation ResultContinued-Simulation Result

Continued-Small Signal Test Continued-Small Signal Test

Signal From the Transmitter (f_input=1kHz)Signal From the Transmitter (f_input=1kHz)

Vtransmitter=49.60mVVtransmitter=49.60mV

Vantenna=25.2mVVantenna=25.2mV

Vreceiver=1.84mvVreceiver=1.84mv

F(-3db)=298.7kHzF(-3db)=298.7kHz

Insertion Loss=-6DB Isolation Loss=-31.50DBInsertion Loss=-6DB Isolation Loss=-31.50DB

Signal From the Receiver (f_input=1kHz)Signal From the Receiver (f_input=1kHz)

Vantenna=49.8mVVantenna=49.8mV

Vreceiver=43mvVreceiver=43mv

Vtransmitter=0mVVtransmitter=0mV

F(-3db)=805.3kHzF(-3db)=805.3kHz

Insertion Loss=-1.27DB Isolation Loss=-InfInsertion Loss=-1.27DB Isolation Loss=-Inf

Continued Large Signal TestContinued Large Signal Test

Signal From the Transmitter (f_input=1kHz)Signal From the Transmitter (f_input=1kHz)

The largest input signal before distortion is 11.5VThe largest input signal before distortion is 11.5V

Signal From the Receiver (f_input=1kHz)Signal From the Receiver (f_input=1kHz)

The largest input signal before distortion is 4.0VThe largest input signal before distortion is 4.0V

Clipping DistortionsClipping Distortions

Continued-BandwidthContinued-Bandwidth

Vantenna 50mV 500mV 1V 4V

-3DB Voltage 35.4mV 353.56mV 0.707V 2.828V

Bandwidth(KHz) 871.5 805.4 757.2 1.32

Basic Model3-Port, Symmetric, Op-Amp

Topology

Purpose:Purpose:To understand the limiting factors involved with Op-Ampsused in this topology

Method:Method:Push the limits of readily available LM741 Op-Amps, to betterunderstand the capability of this topology.

Testing ResultsSmall Signal Test:Small Signal Test:

RRoo: 11k V: 11k VBIASBIAS: +/- 20 DC : +/- 20 DC

VVtrtr : 250mV : 250mVpppp V Vantant(-3dB) occurred at 180 kHz (-3dB) occurred at 180 kHz

Large Signal Test:Large Signal Test:

RRoo: 11k V: 11k VBIASBIAS: +/- 20 DC : +/- 20 DC

VVtrtr : 17V : 17Vpppp V Vantant(-3dB) never occurred, clipping(-3dB) never occurred, clipping

Clipping occurred at 8kHz, yielding calculated slew rate of .427 V/usClipping occurred at 8kHz, yielding calculated slew rate of .427 V/us

Isolation:Isolation:

Ideal operating condition, 1 VIdeal operating condition, 1 Vpppp @ 1 kHz : -23.7 dB @ 1 kHz : -23.7 dB

Small Signal max frequency: -10.17 dBSmall Signal max frequency: -10.17 dB

Large Signal max frequency: -29.19 dB Large Signal max frequency: -29.19 dB

Alternative Model

This model was determined to be too finicky with resistance mismatching. Far too much distortion was found in the experiments, and the topology was abandoned

QuickTime™ and a decompressor

are needed to see this picture.

The input was a sinusoid…

Topology Modeled for our purpose, not a true circulator

Simulation Results

Testing ResultsSmall Signal Test:Small Signal Test:

RRoo: 11k V: 11k VBIASBIAS: +/- 20 DC : +/- 20 DC

VVtrtr : 200mV : 200mVpppp V Vantant(-3dB) occurred at 224 kHz (-3dB) occurred at 224 kHz

Large Signal Test: Large Signal Test:

RRoo: 11k V: 11k VBIASBIAS: +/- 20 DC : +/- 20 DC

VVtrtr : 1V : 1Vpppp V Vantant(-3dB) occurred at 200kHz(-3dB) occurred at 200kHz

•Dr. Young mentioned frequency should be our focus, not power, Dr. Young mentioned frequency should be our focus, not power,

hence, the significantly smaller large signal voltage.hence, the significantly smaller large signal voltage.

Isolation:Isolation:

Ideal operating condition, 1 VIdeal operating condition, 1 Vpppp @ 1 kHz : -25.03 dB @ 1 kHz : -25.03 dB

Small Signal max frequency: -29.05 dBSmall Signal max frequency: -29.05 dB

Large Signal max frequency: -49.11 dB Large Signal max frequency: -49.11 dB

Summary

Pros:

Simplest design

Specifications easiest realized

Cons:Voltage divider

Frequency limited to available Op Amps

Heating Issue

Phase shift at frequency limits

ConclusionConclusion

There are many paths we can take.There are many paths we can take.

Pursue high power: Op/Diff amp designPursue high power: Op/Diff amp design

Pursue high frequency: 3 transistorPursue high frequency: 3 transistor

Pursue a compromise…Pursue a compromise…

We recommend the Op/Diff amp design We recommend the Op/Diff amp design because it is the most realizable.because it is the most realizable.

Questions?Questions?