Designing a CMOS operational amplifier: IC desing by superficial computer aided analysis
Toivanen, Petteri (2021)
Toivanen, Petteri
2021
Tieto- ja sähkötekniikan kandidaattiohjelma - Bachelor's Programme in Computing and Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2021-05-24
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202105235318
https://urn.fi/URN:NBN:fi:tuni-202105235318
Tiivistelmä
Operational amplifiers are widely used electronic components. They implement diverse functions in circuits, like arithmetic operations or signal generation. The operational amplifier itself is technically only an amplifying device and the desired operations are controlled by the external components connected around it. General operational amplifier properties include high amplification, high input impedance and low output impedance.
The target of this work is to design an operational amplifier that works with 2.2 V supply voltage and maximum idle current of 500 µA in integrated circuit use. Minimum load resistance target is 100 Ω. The amplifier is designed with free circuit simulator LTspice and elementary circuit theory.
An existing amplifier structure of Texas Instruments LM358 is used as structural reference. Bipolar junction transistors of LM358 are replaced with field-effect transistors because they are better suited for integrated circuits’ needs due to lower operating currents and supply voltages as well as simpler transistor structure. Ideal components are replaced with respective transistor configurations when practical, pursuing realistic integrated circuit design.
The design is executed with emphasis on iterative graphic analysis. Input stage’s transistors’ operation regions are estimated, after which the suitable operating point is iterated by changing transistor geometries. The buffer and output stage transistor sizing is done by interpreting bias currents and voltages obtained by initial guess. Transistor current and voltage plots are used to inspect individual transistor operating points and block functionality is evaluated by examining signal propagation of a sinusoidal input.
The amplifier designed in this thesis works with 2.2 V supply voltage with 100 Ω load in simulated test circuits. It offers 59.7 dB gain for bandwidth of 11.9 kHz with internal compensation. Idle current of the amplifier settles in 634 µA so the targeted minimum 500 µA is exceeded. Equal comparison in performance of simulated and manufactured operational amplifier proved unreasonable due to excessive effort of simulating process variations’ effect.
The target of this work is to design an operational amplifier that works with 2.2 V supply voltage and maximum idle current of 500 µA in integrated circuit use. Minimum load resistance target is 100 Ω. The amplifier is designed with free circuit simulator LTspice and elementary circuit theory.
An existing amplifier structure of Texas Instruments LM358 is used as structural reference. Bipolar junction transistors of LM358 are replaced with field-effect transistors because they are better suited for integrated circuits’ needs due to lower operating currents and supply voltages as well as simpler transistor structure. Ideal components are replaced with respective transistor configurations when practical, pursuing realistic integrated circuit design.
The design is executed with emphasis on iterative graphic analysis. Input stage’s transistors’ operation regions are estimated, after which the suitable operating point is iterated by changing transistor geometries. The buffer and output stage transistor sizing is done by interpreting bias currents and voltages obtained by initial guess. Transistor current and voltage plots are used to inspect individual transistor operating points and block functionality is evaluated by examining signal propagation of a sinusoidal input.
The amplifier designed in this thesis works with 2.2 V supply voltage with 100 Ω load in simulated test circuits. It offers 59.7 dB gain for bandwidth of 11.9 kHz with internal compensation. Idle current of the amplifier settles in 634 µA so the targeted minimum 500 µA is exceeded. Equal comparison in performance of simulated and manufactured operational amplifier proved unreasonable due to excessive effort of simulating process variations’ effect.
Kokoelmat
- Kandidaatintutkielmat [7052]