2.Opamp parameters
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This document discusses operational amplifier (op-amp) parameters. It describes that an ideal op-amp has infinite input impedance and gain, zero output impedance and noise, and no offset voltage. However, practical op-amps have finite parameters including limited gain, nonzero output impedance and noise, and input offset voltage. It then defines and explains key op-amp parameters such as common-mode rejection ratio, input offset voltage, bias current, impedance, slew rate, and how they characterize real op-amp performance compared to ideal specifications.
2.Opamp parameters
- 1. Analog Integrated CircuitsAnalog Integrated Circuits ECL 515 / ECL(X) 315ECL 515 / ECL(X) 315 Op amp Parameters 1 Sem-VII 90 INAC-L & X AT2015 Prof.Satheesh Monikandan.B HOD-ECE Indian Naval Academy, Ezhimala [email protected]
- 2. Introduction 2 Op-amp schematic symbol One Output Terminal Two Input Terminals Inverting input Non-inverting input Two Power Supply (PS) +V : Positive PS -V : Negative PS
- 3. 3 Applications of Op-Amp To provide voltage amplitude changes (amplitude and polarity) Comparators Oscillators Filters Sensors Instrumentation amplifiers
- 4. Stages of an op-amp 4 INPUT STAGE OUTPUT STAGE GAIN STAGE
- 5. Infinite input impedance Zero output impedance Infinite open-loop gain Infinite bandwidth Zero noise contribution Zero DC output offset 5 Ideal Op-Amp Practical Op-Amp Input impedance 500k-2MΩ Output impedance 20-100 Ω Open-loop gain (20k to 200k) Bandwidth limited (a few kHz) Has noise contribution Non-zero DC output offset Properties
- 6. 6 Zero Noise Contribution In an ideal op amp, all noise voltages produced are external to the op amp. Thus any noise in the output signal must have been in the input signal as well. The ideal op amp contributes nothing extra to the output noise. In real op-amp, there is noise due to the internal circuitry of the op-amp that contributes to the output noise.
- 7. Op-Amp Parameters COMMON-MODE REJECTION (CMRR) COMMON-MODE INPUT VOLTAGE INPUT OFFSET VOLTAGE INPUT BIAS CURRENT INPUT IMPEDANCE INPUT OFFSET CURRENT OUTPUT IMPEDANCE SLEW RATE 7
- 8. Common-Mode Rejection Ratio (CMRR) The ability of amplifier to reject the common-mode signals (unwanted signals) while amplifying the differential signal (desired signal). Ratio of open-loop gain, Aol to common-mode gain, Acm CMRR= Aol Acm CMRR=20 log ( Aol Acm ) 8 The higher the CMRR, the better, in which the open-loop gain is high and common-mode gain is low. CMRR is usually expressed in dB & decreases with frequency.
- 9. 9 Input Offset Voltage Ideally, output of an op-amp is 0 Volt if the input is 0 Volt. Realistically, a small dc voltage will appear at the output when no input voltage is applied. Thus, differential dc voltage is required between the inputs to force the output to zero volts. This is called the Input Offset Voltage, Vos. Range between 2 mV or less.
- 10. Input Bias Current Ideally should be zero. The dc current required by the inputs of the amplifier to properly operate the first stage. Is the average of both input currents. 10
- 11. Input Impedance Is the total resistance between the inverting and non-inverting inputs. Differential input impedance : total resistance between the inverting and non-inverting inputs. Common-mode input impedance: total resistance between each input and ground. 11
- 12. Input Offset Current It is the difference of input bias currents. Ios=∣I1−I2∣ 12 V os=I1 Rin−I2 Rin=(I 1−I 2)Rin V os=Ios Rin V out(error)=Av Ios Rin Input offset current Offset voltage Thus, error
- 13. Slew Rate It is the maximum rate of change of the output voltage in response to a step input voltage. SlewRate= ΔV out Δt 13 where ΔVout =+V max−(−V max )
- 14. Slew Rate It’s a measure of how fast the output can “follow” the input signal. 14
- 15. Example Determine the slew rate: SlewRate= ΔV out Δt 15 SlewRate= +9V−(−9V) 1μs =18V / μs