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RC Op-Amp Circuits (6.4)

RC Op-Amp Circuits (6.4). Dr. Holbert April 10, 2006. Digital Meters and Oscilloscopes. Most multimeters and oscilloscopes are now digital. A digital multimeter or a digital oscilloscope has an analog-to-digital (A/D) converter.

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RC Op-Amp Circuits (6.4)

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  1. RC Op-Amp Circuits (6.4) Dr. Holbert April 10, 2006 ECE201 Lect-18

  2. Digital Meters and Oscilloscopes • Most multimeters and oscilloscopes are now digital. • A digital multimeter or a digital oscilloscope has an analog-to-digital (A/D) converter. • Most digital meters and all digital oscilloscopes have one or more processors. ECE201 Lect-18

  3. Data Acquisition Systems • In many applications, digital meters and scopes are being replaced by data acquisition cards that fit into a computer. • The data acquisition cards have A/D converters. • The computer provides processing and storage for the data. ECE201 Lect-18

  4. A Generic Digital Meter Input Switching and Ranging A/D Converter Amplifier Display Processor ECE201 Lect-18

  5. Voltage Measurements 100V 10V 1V Hi Com ECE201 Lect-18

  6. Ideal Meter Hi 10MW Com Model for Meter The ideal meter measures the voltage across its inputs. No current flows into it; it has infinite input resistance. ECE201 Lect-18

  7. Ideal Meter Hi R 10MW Com Meter Loading The 10MW meter resistance in parallel with R may change the voltage that you measure. ECE201 Lect-18

  8. Loading • When measuring the voltage across R, we need to make sure that R is much less than 10MW. • If R is close to 10MW, significant current flows through the meter, changing the voltage across R. ECE201 Lect-18

  9. Loading Example • Without Meter: voltage is 100V • With Meter: measured voltage is 83.3V Ideal Meter Hi 50mA 2MW 10MW Com ECE201 Lect-18

  10. Current Measurements 100V 10V 1V Com Amp ECE201 Lect-18

  11. Measuring Large Currents (> 100mA) • The current to be measured is passed through a small resistor (called a shunt resistor) and the resulting voltage across the shunt resistor is measured. • From the voltage, the current can be computed. ECE201 Lect-18

  12. Meter Loading The Rs shunt resistance in series with R may change the current that you measure. Ideal Meter Amp Rs R Com ECE201 Lect-18

  13. + – The Voltage Follower + + – vin vout – ECE201 Lect-18

  14. RA/D Without a Voltage Follower Rs vA/D is not equal to vs + A/D Converter + – Sensor vs vA/D – ECE201 Lect-18

  15. Op-Amp Review • The ideal op-amp model leads to the following conditions: i+ = i- = 0 v+ = v- • The op amp will set the output voltage to whatever value results in the same voltages at the inputs. ECE201 Lect-18

  16. Op-Amp Review • To solve an op-amp circuit, we usually apply KCL (nodal analysis) at one or both of the inputs. • We then invoke the consequences of the ideal model. • We solve for the op-amp output voltage. ECE201 Lect-18

  17. RA/D With a Voltage Follower vA/D is equal to vs + + + – – Rs vs vA/D – Sensor A/D Converter ECE201 Lect-18

  18. An Integrator C R – + – + + Vin Vout – ECE201 Lect-18

  19. KCL at the Inverting Input C iC(t) R – iR(t) i- + – + + vin(t) vout(t) – ECE201 Lect-18

  20. KCL ECE201 Lect-18

  21. Solve for vout(t) ECE201 Lect-18

  22. Class Example • Learning Extension E6.9 ECE201 Lect-18

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