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Analog Electronics Workshop Slew Rate

Analog Electronics Workshop Slew Rate. March 13, 2013. Remember Capacitor Physics! Constant Current  Voltage Changes Linearly. slope of straight line function. Slew Limit. For slow moving or small signals i OUT < i OUT (max ) For large, rapid moving signals i OUT = i OUT (max )

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Analog Electronics Workshop Slew Rate

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  1. Analog Electronics WorkshopSlew Rate March 13, 2013

  2. Remember Capacitor Physics!Constant Current Voltage Changes Linearly slope of straight line function

  3. Slew Limit • For slow moving or small signals iOUT< iOUT(max) • For large, rapid moving signals iOUT= iOUT(max) • The output is slew rate limited • This is the fastest rate the output can change • The input is no longer a virtual short • Large input differential voltages are possible • iOUTis constant, so VOUTincreases linearly across capacitor CC

  4. Slew Rate – Inside the Amplifier

  5. Slew Rate of Different Amplifiers

  6. Simulate Slew Rate - OPA2188 Look at the slope of the output signal. The rate of change is the slew rate.

  7. Simulate Slew Rate - OPA2188 The input no longer is a virtual short. The output changes can not keep up with the input.

  8. Large Signal Step Response OPA827(Shows Slew Rate and Settling Time) SR = 10V / 0.4µs = 25 V/µs (from graph) SR = 28 V/µs (from data sheet table)

  9. Slew Rate over Temperature

  10. Slew Boost Slows down as VOUTapproaches VIN.

  11. Current to Miller Capacitance IccWith and Without Slew Boost

  12. Max Output vs. Freq Full Power BW

  13. Maximum Output vs Frequencyalso called Full Power Bandwidth For Vs = +/-15V 10Vpk Distortion! 7.5Vpk No Distortion!

  14. No Slew Induced Distortion7.5Vpk Output Swing

  15. No Slew Induced Distortion10Vpk Output Swing

  16. Derivation of Maximum Output vs. Freq Relationship Hand Calculation matches graph.

  17. Slew Rate Lab • Simulation • Calculation • Measurement

  18. Ex 4.1: Hand Calculations 1. Draw the output waveform for the circuit below.

  19. Ex 4.1: Slew Rate PCB Schematic U1 is configured as a buffer for these examples. R6 is not installed and R5 is a short. In the top position J2 will connect the scope channel 0 to the output of U1 (as shown). In the bottom connection scope channel 0 is connected to the input signal for U2. U2 is configured for a gain of -34.8. This circuit will be used for bandwidth tests. The myDAQ provides +/-15V dc supplies. The circuit to the left is used to regulate the supplies to +/-2.5V.

  20. Ex 4.1: Amplifier I/O PCB Setup Install OPA333 into socket U1 Set jumper J2 to top position: U1 Out to AI(0+)

  21. Ex 4.1: Instrument Setup The instrument setup above will configure the signal source and scope for the circuit below so that we can see the slew rate limitations.

  22. Ex 4.1: Expected Results Run transient analysis with the Tina circuit called “04-AWE-opa333-SR.tsc” Use the cursors on the myDAQ and Tina Spice tool to measure the slew rate (rise / run).

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