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OBIOMA CHIMA oc5118@ic.ac.uk 8263 4684 OPERATIONAL AMPLIFIERS A MedED LECTURESESSION STRUCTURE Characteristics of ideal Questions opamps Different OPAMP configurations What is an OP AMP • These are devices that amplify an input vintage (V ) and produce an outputVoltagoutV ) by a scale factorA • Comprised of transistors, capacitors and resistors but represented by this simple schematic • To operate, they require connection to an external power source (Vs+ andVs-) • These are usually emitted from schematic drawings IMPORT ANT EQUA TIONS • A OLthe open loop gain (scale factor of amplification), is a ratio outV in A =V /V OL out in • V in the difference between the inverting and non-inverting terminals (V -V) + - Assumptions of an ideal OP AMP 1. The open -loop gain is very large (A => ∞), 4 6 OL often in the range of 1 10 Iin 0A 2. The input terminals have infinite resistance so no current flows into them 3. In closed-loopconfigurations, the inverting (V-) and non-inverting (V+) terminals are connected via a virtual shor -t ircui(the voltages going into both terminals is temore on this later) Characteristics of OP AMPs • The output of an OPAMP is limited by the maximum positive and negative values of the power supplys+V andVs- • For instance, if a 5V power source was used to power the opamp, the amplified output signal wousdturate at ±5V (V ≤ 5V) out • The response of an opamp has a linearand saturation region • TheVin (diff between terminals) atwhichtheopampsaturatesis usually in the order of ±100µVSESSION STRUCTURE Characteristics of ideal Questions opamps Different OPAMP configurations CONFIGURATION 1: The Comparator • An open-loopconfiguration • A simple way to compare the magnitude of the two input signals • A OLx (V+-V)-=V out • We know open-loop gain,A , OL very large, so even small changes in the input terminals can cause large voltages attheoutput,oftenleadingtosaturation • For example, IfV+= 3.00V andV -3.001V ,Voutould be: 6 A OLx (- 100μV) and for a gain of 10 and rails of-5V and +5V , the output signal out) would saturate at -5V • This indicates thatV+V - • A maximum positiveVout would indicateV >V- + CONFIGURATION 2: Voltage Follower • A closed-loopconfiguration • This is an OPAMP circuit in which the input voltage is EQUAL to the output voltage • This configuration is used to provide the same voltage to a load without drawing any current due to its high input resistance CONFIGURATION 3: Inverting Amplifier • This is used when smaller gains are required • This produces an output voltage with an inverted polarity to the input voltage • This is achieved by feeding some of the output back to the V- (inverting) terminal of the opamp and grounding the non-inverting terminal (V+) CONFIGURATION 4: Non - Inverting Amplifier • This produces an output voltage without an inverted polarity to the input voltage (polarity is the same) • This is achieved by feeding some of the output back to th- V (inverting) terminal of the opamp and grounding the inverting terminal (V-) Here, the gain is controlled by adjusting the magnitude of the 2 resistorsSESSION STRUCTURE Characteristics of ideal Questions opamps Different OPAMP configurationsQuestion Open-loop gain is 10Question What configuration is shown here?OPAMPs: Summary slide Characteristics Important OPAMP configurations 1. Voltage follower (V =V in out • Open-loop gain is very large 2. Comparator • Input terminals 3. Inverting Amplifier have infinite 4. Non-inverting Amplifier resistance • In closed-loop OPAMPs, theV+ andV- terminals are connected via a virtual shortTHANKYOU FOR COMING! PLEASE FILL IN THE FEEDBACK FORM!MedED lecture masterslide COLOURS FONTS Red banner: #C20101 Titles:AHRONI Blue background: #1D5F97 Subtitles: ARIAL Grey background: #D9D9D9 Text: ARIAL White/ black writing