4. OPERATIONAL AMPLIFIERS CIRCUITS by Ulaby & Maharbiz

Overview

Tech Brief 7: IC Fabrication Wafer: Thin slice of semiconductor material with highly polished surface Processed wafer is cut into many dies or chips. Lithography: Defining spatial pattern Photoresist: Polymer material that does not allow etching or deposition of areas underneath it.

Tech Brief 7: IC Fabrication

Lithography: Defining spatial pattern Photoresist: Polymer material that does not allow etching or deposition of areas underneath it. Tech Brief 7: IC Fabrication

Operational Amplifier “Op Amp”  Two input terminals, positive (non- inverting) and negative (inverting)  One output  Power supply V +, and Op Amp showing power supply Op Amp with power supply not shown (which is how we usually display op amp circuits)

Inside The Op-Amp (741)

Gain  Key important aspect of op amp: high voltage gain  Output, A is op-amp gain (or open-loop gain) – different from circuit gain G  Linear response

Equivalent Circuit

Example 4-1: Op Amp Amplifier KCL at Node a: KCL at Node b: For infinite A: = = 5 Node a Node b

Negative Feedback  Feedback: return some of the output to the input  Negative feedback decreases input signal  Achieves desired circuit gain, with wide range for input Negative Feedback No Feedback Range of 5 Gain = 5Range of : ‒ 2 V to +2 V Gain = 1million Range of : ‒ 10 mV to +10 mV

Circuit Analysis With Ideal Op Amps  Use nodal analysis as before, but with “golden rules”   N  Do not apply KCL at op amp output No current into op amp No voltage drop across op amp input

Noninverting Amplifier (max) = V cc At node

Inverting Amplifier

Example 4-2: Input Current Source Relate output voltage to input current source

Summing Amplifier

Example 4-4: Solution:

Difference Amplifier Note negative gain of channel 1

Voltage Follower “Buffers” Sections of Circuit What is the op amp doing? depends on both input and load resistors is immune to input and load resistors

Example 4-5: Elevation Sensor Sensor Response Desired Output h = elevation, inversely proportional to air pressure

Example 4-6: Multiple Op-Amp Circuit

Measurement Uncertainty (T = 21 ° C) v2v2 V 0 = V 2 ± 1% of V 2 21 ° C ± 0.21 ° C G = 1 ± 1% G = 1 1% G = 1 1% v2v2 (T = 21 ° C) Thermistor v1v1 Fixed Reference Temp = 20 ° C V 0 = (V 2 ‒ V 1 ) ± 1% of (V 2 ‒ V 1 ) 1 ° C ± 0.01 ° C Direct Measurement Differential Measurement Much better measurement uncertainty

Instrumentation Amplifier Highly sensitive differential amplifier

Digital to Analog Converter Converts digital value into analog voltage 4-digit example

Digital to Analog Converter Represent digital value with analog voltage

MOSFET (Field Effect Transistor) Active Device: Voltage Controlled Current Source Gate voltage controls drain/source current

MOSFET Equivalent Circuit Characteristic curvesIdealized response

Example 4-9: MOSFET Amplifier Given: Determine

Load Line You can use a “load line” to graphically determine V out = V DS for a given V in = V GS RLRL V DD V DD / R D

Digital Circuit: MOSFET Inverter V DD = 15 V RLRL G S D IDID Output “High” Logic 1 Output “Low” Logic 0 InOut Input “Low” InOut V DD V GS =V in V DS =V out Output “Low” Logic 0 Output “High” Logic 1 Input “High”

Read-Only Memory (ROM) Circuits V READ = 1 V BIT = 0100

Another Digital Circuit Element: NAND ABOut A B V DD A V out B No current flows through resistor, unless both A and B inputs turn their transistors on to “pull down” V out NAND gates can be used to build any binary logic function

Another Digital Circuit Element: NOR Current will flow if either A or B inputs turn their transistors on to “pull down” V out ABOut A B A V DD V out B NOR gates can be used to build any binary logic function

Tech Brief 8: Electromagnetic Spectrum

Example: Multisim Instruments

Multisim Table

Multisim: MOSFET I-V Analyzer

Summary