1. OPA348 High Pass Filter Tim Green, MGTS Precision Linear Analog Applications July 9, 2015 1

2. 2 Summary 1) See included schematic of your circuit. At 159Hz you will find the Vout/Vin Transfer function measured out of Voa2 is -6dB down at your high pass filter of 159Hz. Correspondingly you can measure the gain at any frequency by using the free SPICE Simulator I reference at the end. At 400Hz Voa2/VG1 = 38.798613dB = x87 (not x100)! 2) I also provide mathematics for computing magnitude at any frequency. 3) Low pass roll-off is due to the closed loop gain of 10 intersecting op amp Aol. See TIPL link below for details: http://www.ti.com/lsds/ti/amplifiers-linear/precision-amplifier-precision-labs.page?DCMP=tipl&HQS=hpa-pa-opamp-tipl-vanity-tr-en Look at the ones on Bandwidth. 4) You may or may not be able to connect your existing circuit directly your ADC input and get <1/2 LSB error each time you acquire a sample. Let me know which ADC you are using, ADC reference voltage, conversion and acquisition time. I can help guide you to get it right by design.

3. 3 OPA348 High Pass Filter

4. Bode Plot Gain and Phase Calculations Tim Green Precision Linear Analog Applications August 5, 2013 4

5. Typical Pole and Typical Zero 5

6. TINA Simulation 6 Magnitude: Pole A:(400; -644.622921m) B:(4k; -12.30451) Zero A:(400; 644.622918m) B:(4k; 12.30451) Phase: Pole A:(400; -21.801708) B:(4k; -75.963501) Zero A:(400; 21.801708) B:(4k; 75.963501) AC Simulation run with 1000 points. Correlation with Calculation depends on number of points used for simulation

7. Simulation versus Calculated Results 7 Magnitude: Pole A:(400; -644.622921m) B:(4k; -12.30451) Zero A:(400; 644.622918m) B:(4k; 12.30451) Phase: Pole A:(400; -21.801708) B:(4k; -75.963501) Zero A:(400; 21.801708) B:(4k; 75.963501)

8. Formulae for Pole and Zero Calculations 8

9. Closed Loop Gain: Magnitude and Phase 9

10. Closed Loop Gain: Magnitude and Phase: 2 Pole, 2 Zero Calculator 10

11. Op Amp Stability Reference For detailed, definition-by-example of 10 different ways to stabilize op amps driving capacitive loads, and additional technical information on solving op amp stability problems, visit the Texas Instruments E2E Forum at: http://e2e.ti.com/support/amplifiers/precision_amplifiers/w/design_notes/ 2645.solving-op-amp-stability-issues.aspx Download Part 1, Part 2, Part 3, and Part 4. 11 All Embedded Schematics in this presentation can be run in the Free TINA_TI SPICE simulator available at: http://www.ti.com/tool/tina-ti