Transcript Document
electronics fundamentals circuits, devices, and applications THOMAS L. FLOYD DAVID M. BUCHLA Chapter 20 (IA) and Flash ADC Electronics Fundamentals 8th edition Floyd/Buchla © 2010 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved. Chapter IA and Flash 1 ADC Instrumentation amplifiers An instrumentation amplifier (IA) is a special integrated circuit designed for applications where small signals are in noisy environments. They have high input impedance and a high CMRR for excellent noise rejection. R3 to R6 are equal Vin1 + Vcm values. If R1 = R2, then the closed-loop gain is set by a single R external resistor, RG, G supplied by the user. The gain is: Acl 1 2R Vin2 + Vcm R3 + - R 1 - R2 + R5 R4 Vout = Acl (Vin2-Vin1) + R6 RG Electronics Fundamentals 8th edition Floyd/Buchla © 2010 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved. Chapter IA and Flash 1 ADC Instrumentation amplifiers For R1 = R2 = 10 kW, what value of RG will set the gain to 40? Acl 1 Vin1 2R RG - R 1 Solving for RG, RG RG RG 2R 40 - 1 513 W Vin2 + R5 - R2 Acl - 1 2 10 k W R3 + R4 Vout + R6 (510 W is the nearest standard value). Electronics Fundamentals 8th edition Floyd/Buchla © 2010 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved. Chapter IA and Flash 1 ADC Instrumentation amplifiers The bandwidth of instrumentation amplifiers decreases when higher gain is selected. The frequency response is published by the manufacturer. For example the frequency response of an INA333 is shown. If the required frequency response is less than about 300 Hz, a gain of 1000 can be selected. The INA333 can operate on as little as 1.8 V, so is used in portable medical, handheld instrumentation, weigh scales and data acquisition applications. Electronics Fundamentals 8th edition Floyd/Buchla © 2010 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved. Chapter IA and Flash 1 ADC Flash Analog-To-Digital Converter Comparators can be used to convert analog-to-digital (AD) signals. The Flash AD Converter or Direct Conversion ADC, are simple and extremely fast AD converters. More comparators are needed as the required bit-precision increases: 2n-1 comparators for nbits of precision. Electronics Fundamentals 8th edition Floyd/Buchla © 2010 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved. Chapter IA and Flash 1 ADC Binary-weighted input D/A Converter A weighted inverting summing Operational Amplifier can be used to convert digital-to-analog signals. Setting the 3 input resistor values at multiple powers of two, the output of the operational amplifier represents the analog value of the 3-bit binary data. Electronics Fundamentals 8th edition Floyd/Buchla © 2010 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.