ELECTRICAL ENGINEERING TECHNOLOGY PROGRAM EET 331 – ELECTRONIC DESIGN LABORATORY EXPERIENCES LABORATORY EXPERIENCE: The Instrumentation Amplifier Instrumentation Amplifiers (IA) are used when it is necessary to measure low-level differential signals with a high degree of accuracy. In this laboratory exercise we will design an instrumentation amplifier based on the 3 Op Amp approach and will evaluate the performance of a commercial monolithic IA. SECTION 1.- Instrumentation Amplifier based on Op Amps 1.1 Design an Instrumentation Amplifier based on the 3-OpAmp circuit with the following characteristics: - Differential Gain of 100 - Common-mode Gain as low as possible Note1.- Do not use variable resistances, potentiometers of resistor boxes Note 2.- To avoid the second stage saturating because of offset, distribute the gain between the first and second stages in a convenient way 1.2 Measure the IA's CMRR (Use the techniques learned in the past lab experience to do these measurements) - Comment on the differences between the expected and measured values. - How could you improve the circuit's CMRR? SECTION 2.- Monolithic IAs Monolithic Instrumentation Amplifiers offer an interesting solution to building Instrumentation Amplifiers using Op Amps. Monolithic IAs offer the advantage of integration and resistance matching. Other monolithic IAs have additional advantages, for example the ability to change their gain using different control words. In this section we will study the performance of the PGA202 Instrumentation Amplifier manufactured by Texas Instruments (The PGA202 was first developed and manufactured by Burr-Brown). 2.1 Download, if you haven't done this yet, the specifications for the PGA202 Integrated Circuit 2.2 What is the main difference between the PGA202 and PGA203? EET 331 – Instrumentation Amplifier 1/2EET 331 – Instrumentation Amplifier 2/2 2.3 What are the pins in the PGA202 that are used to control its gain? What is the gain for each combination? 2.4 What is the voltage for a Low and a High that need to be applied to the control pins from section 2.3? 2.5 Design an Instrumentation Amplifier based on the PGA 202 with externally controlled gain. Check with your instructor for possible errors. 2.6 Build the previous circuit. Verify that it is working for all the possible gains (You may need to attenuate the input signal for the highest gains). 2.7 Measure the CMRR of your Instrumentation Amplifier for each one of the possible gains (Give the values for Ad, Acm and CMRR) 2.8 Using the specifications in the data sheet, compare the CMRR values for each gain with the values given by the manufacturer. Keep in mind the effect of frequency in the CMRR as stated in the data sheet. 2.9 Compare the value of CMRR obtained with the 3-OpAmp IA with the CMRR using the monolithic IA. Discuss your results. 2.10 Explain how the Auto Gain Ranging circuit shown in Page 9 in the PGA202 data sheet works. SECTION 3. Laboratory report - Create an individual lab report using the guidelines provided in the course’s website. Include all the information that you believe is necessary. - Once again, please comment on the difficulties and challenges of this laboratory work (i.e. what worked, what did not work, what you liked, what you didn’t like, etc.). Be assured that the grade for your laboratory work or your course will not be affected at all by your positive or negative