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lesson20 - Lesson 20 Op-Amps #5 (Section 4-5) (CLO 4-3)...

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Lesson 20 – Op-Amps #5 (Section 4-5) (CLO 4-3) This lesson is dedicated to Op-Amp application, in particular, D/A and Comparator circuits. The next two lessons are reserved for Instrumentation applications. Digital-to-Analog Converters (DACs or D/As) We will look at two different types of D/A circuits – the weighted summer and the R- 2 R ladder circuit. The first is very easy for students to grasp since it is simply an inverting summer. The figure below is for a 4-bit DAC, but generally, DACs are eight or more bits in length. The output is given by REF 4 3 2 1 F O 8 4 2 V b b b b R R v + + + - = Where each bit drives an electronic switch that switches between ground (0V) and V REF , whatever the designer wants it to be. The simplicity of this design is offset by the accuracy that each resistor must have to make all the bits weighing proportional. In general, this is not the way DACs are designed. Consider instead the R -2 R realization shown in the following circuit. Here the importance is that all resistors be the same R or 2 R . An easy task especially if laid-out on a PC board or thick- or thin-film construction. It is worthwhile to let the students derive the output for a simple 4-bit DAC and they can then
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This note was uploaded on 10/12/2010 for the course MAE 140 taught by Professor Mauriciodeoliveria during the Spring '08 term at UCSD.

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lesson20 - Lesson 20 Op-Amps #5 (Section 4-5) (CLO 4-3)...

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