1. ProtoSmart Board: ADC Input Stage by Clayton Bridge

2. ProtoSmart Board

3. ProtoSmart Board Design Specifications: Voltage Measurement Minimum: - 10V Voltage Measurement Maximum: + 10V Current Measurement Minimum: - 1 A Current Measurement Maximum: + 1 A measured across a 0.2Ω current sense resistor:+/- 0.2V ADC Specifications: ADC Range (IN+ - IN-)Minimum:-2V ADC Range (IN+ - IN-)Maximum:+2V The Problem

4. The Real Problem The Caveat: IN+ and IN- range:0 - 3.3V Summary: ADC wants to see -2 to 2V range DIFFERENCE between IN+ and IN- BUT IN+ and IN- MUST remain between 0 – 3.3V

5. The Solution (Vaguely)

6. The Solution (Mathematically) Minimum Signal Representation: Voltage:-10V Current:-1A (-0.2V across Rsense) IN+0V IN-2V ADC_out-2V Maximum Signal Representation: Voltage:+10V Current:+1A (+0.2V across Rsense) IN+2V IN-0V ADC_out+2V

7. The Solution (Conceptually) What are we doing again? Massage the measurement signal to covert it to a 0-2V range and feed to IN+. Feed (2 – IN+) to IN- Converting ProtoSmart Board measurement range to -2 to 2V for ADC.

8. The Solution (Functionally)

9. The Solution (Electronically)

10. Divide and Conquer How? Examine each function or stage separately and observe their effect on the signal. We will input a 20Vpp sine wave centered at 0V representing the +/-10V measurement signal and observe the output after each stage.

11. Vin: Unity Gain Instrumentation Amplifier

12. V_DIF vout_scaled Scaling Stage: Inverting Amplifier

13. V(vadc+) Shifting Stage: Noninverting Summing Amplifier

14. 2V vadc- VADC- : Unity Gain Instrumentation Amplifier

15. Overall Effect

16. Choosing the Op Amps ProtoSmart Board Specifications Frequency range:< 1MHz Voltage range:+/- 10V Factors to Consider Gain-bandwidth Product Slew Rate Output Voltage Swing Price

17. GBW > 5MHz SR > 7 V/us Rails > -10 to +10V GBW > 1MHz SR > 7 V/us Rails > 0 to +2V GBW > 1MHz SR > 63 V/us Rails > -10 to +10V Specifications to Prevent Distortion GBW > 1MHz SR > 7 V/us Rails > 0 to +2V Rails > 1V

18. I hope you enjoyed this little Pecha Kucha!