EE 435 Lab 2 Spring 2009

EE 435 Lab 2 Spring 2009 - EE435 Experiment 2: Amplifier...

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EE435 Experiment 2: Amplifier Characterization Spring 2009 Objective: The objective of this experiment is to develop measurement methods for characterizing key properties of operational amplifiers 1 Introduction Amplifiers are one of the major components and building block used in analog and mixed-signal circuits. For printed circuit board designs, the designer usually uses discrete operational amplifiers (op amps) that have the ability to drive relatively large capacitive loads which may be a combination of parasitic capacitances from the board traces in addition to any required capacitive load. These discrete op amps are some times called "catalog op amps" and are usually harder to design than op amps that are used as components in larger on-chip systems. The design of catalog op amps is generally more challenging because of the requirement that they be useful in a wide variety of applications that may have varied performance requirements. Invariably this requirement for use in a wide variety of applications requires meeting rather stringent performance requirements on characterization parameters such as dc gain, gain- bandwidth product (GB), slew rate, offset voltage, power consumption, power supply rejection ratio, common mode rejection ratio, etc. In this experiment, several performance parameters, often termed specifications, that are widely used to characterize an op amp will be investigated. These specifications are the offset voltage, Vos , the open loop voltage gain, Ao , the slew rate, SR, and the gain bandwidth product, GB . These specifications will be measured for both the commercial uA741 operational amplifier and the single-ended push-pull amplifier shown in Fig. 1. A standard CMOS inverter such as a C4004 or a MOS transistor array, the CD 4007, can be used to build the push-pull amplifier. Although these CMOS devices are in old technology, they should work well for this amplifier application. Fig. 1 Single-ended Push-Pull Amplifier Stability and compensation are also key issues that must be addressed when designing and using operational amplifiers. Although it is premature to discuss these concepts in detail at this point in the course, issues surrounding stability and compensation will be investigated experimentally in this experiment as well. Page 1 of 7
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2 Performance Parameter Measurements 2.1 Open Loop Gain, Ao Most operational amplifiers are designed to have a single-pole lowpass response that can be expressed as () 0 A As s 1 p = + ( 1 ) where A 0 is the dc gain of the operational amplifier and where p is the location of the dominant pole. A(s) is often referred to as the open-loop gain of the op amp. In most internally compensated op amps, the pole p is in the range of 10rad/sec. By definition, the gain-bandwidth product, GB, is given by the expression GB=A 0 p ( 2 ) Measure the open loop gain, A 0 , of the 741 operational amplifier and of the push- pull amplifier shown in Fig. 1. Make a comparison of these measured results with those
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This note was uploaded on 01/31/2012 for the course EE 345 taught by Professor Geiger during the Fall '11 term at Iowa State.

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EE 435 Lab 2 Spring 2009 - EE435 Experiment 2: Amplifier...

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