Analog Electronics Workshop Input/Output Limitations Rev 0.2 March 13, 2013

What’s Wrong?

Common Mode Voltage Definition

Vcm Input and Output Swing Vcm Range Vout Output Swing

Vcm – Two Examples Vcm = 0V Vcm = 5V

Input Stage V BE V SAT Output Stage

Translating the Data Sheet -2.6V< Vcm < 1.0V -2.95< Vout < 2.95V -2.6V< Vcm < 1.0V ParameterConditionsMinTypMaxUnit Input Voltage Range Common-Mode Voltage Range V CM (V-) – 0.1V(V+)-1.5V Output Voltage Output VoutRL = 10kΩ2050mV

Vcm or Output Swing Problem? Remember -2.95V<Vout<2.95V -2.6V<Vcm<1.0V What is the common-mode voltage? This is a Vcm violation! Vcm=Vin!

Measurement 9

NI myDAQ Exercise-Vcm Populate U1 with OPA735 Set J2 to 1-2 position

NI myDAQ Exercise-Vcm Launch Scope Scope Settings –Scale V/Div = 500mV –Time/Div = 200us –Trigger Type = Edge Run

NI myDAQ Exercise-Vcm Launch FGEN FGEN Settings –Triangle Wave –Frequency=1kHz –Amplitude=4Vpp –Signal Route=AO(1) Run

Further Reading

NI myDAQ Exercise-Vcm TINA ResultsLab Results

Simulation Measurement 15

TINA Exercise

Vin SettingsTriangular Wave Settings

TINA Exercise Analysis->Transient View->Separate Curves

Vcm or Output Swing Problem? For OPA V<Vout<1.3V (RL=10k) -0.5V<Vcm<0.5V What is the common-mode voltage? We can’t violate Vcm in this configuration! Vcm=0V! Output Swing Violation!

NI myDAQ Exercise-Output Swing Populate U2 with OPA277 Inverting Configuration

NI myDAQ Exercises Output Swing Stop Scope Settings –Source=AI(1) –Scale V/Div = 500mV –Time/Div = 200us –Trigger Type = Edge Run

NI myDAQ Exercise Output Swing Stop FGEN Settings –Triangle Wave –Frequency=1kHz –Amplitude=160mVpp Signal Route=AO(0) Run

NI myDAQ Exercise Output Swing TINA ResultsLab Results

24

1. For the circuit below: The output reads -260mV. The offset is 30uV typical. Why is the output so large?

1. For the circuit below: The output reads 171mV. The offset is 30uV typical. Why is the output so large?

Revisions 0.2 –Added homework –Added Lis / Kay presentation on limits.