OPA 348 High Pass Filter Tim Green MGTS

OPA 348 High Pass Filter Tim Green, MGTS Precision Linear Analog Applications July 9, 2015 1

Summary 1) See included schematic of your circuit. At 159 Hz you will find the Vout/Vin Transfer function measured out of Voa 2 is -6 d. B down at your high pass filter of 159 Hz. Correspondingly you can measure the gain at any frequency by using the free SPICE Simulator I reference at the end. At 400 Hz Voa 2/VG 1 = 38. 798613 d. B = x 87 (not x 100)! 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. 2

OPA 348 High Pass Filter 3

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

Typical Pole and Typical Zero 5

TINA Simulation Magnitude: Pole A: (400; -644. 622921 m) B: (4 k; -12. 30451) Zero A: (400; 644. 622918 m) B: (4 k; 12. 30451) Phase: Pole A: (400; -21. 801708) B: (4 k; -75. 963501) Zero A: (400; 21. 801708) B: (4 k; 75. 963501) AC Simulation run with 1000 points. Correlation with Calculation depends on number of points used for simulation 6

Simulation versus Calculated Results Magnitude: Pole A: (400; -644. 622921 m) B: (4 k; -12. 30451) Zero A: (400; 644. 622918 m) B: (4 k; 12. 30451) Phase: Pole A: (400; -21. 801708) B: (4 k; -75. 963501) Zero A: (400; 21. 801708) B: (4 k; 75. 963501) 7

Formulae for Pole and Zero Calculations 8

Closed Loop Gain: Magnitude and Phase 9

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

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 E 2 E Forum at: http: //e 2 e. 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. 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 11