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Chapter 20 (IA) and Flash ADC

electronics fundamentals. circuits, devices, and applications. THOMAS L. FLOYD DAVID M. BUCHLA. Chapter 20 (IA) and Flash ADC. Instrumentation amplifiers.

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Chapter 20 (IA) and Flash ADC

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  1. electronics fundamentals circuits, devices, and applications THOMAS L. FLOYD DAVID M. BUCHLA Chapter 20 (IA) and Flash ADC

  2. 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 values. If R1 = R2, then the closed-loop gain is set by a single external resistor, RG, supplied by the user. The gain is: Vin1 + Vcm + R3 R5 - R1 Vout = Acl (Vin2-Vin1) - RG R2 + - R4 Vin2 + Vcm + R6

  3. Instrumentation amplifiers Example: For R1 = R2 = 10 kW, what value of RG will set the gain to 40? Solution: Vin1 + R3 R5 - R1 Solving for RG, - Vout RG R2 + - R4 + 513 W R6 Vin2 (510 W is the nearest standard value).

  4. 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 300Hz, 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.

  5. 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 n-bits of precision.

  6. 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.

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