The document describes the goals, specifications, tasks, and test plan for a student project to build a frequency-tunable hearing aid. The goals are to build a hearing aid that can amplify different frequency ranges selected by the user. The device will split the input signal into four frequency bands and amplify each band separately before summing the signals. The document outlines the circuit components, including op-amps, filters, and programmable gain amplifiers. It also provides analysis of the circuit's performance with graphs of the gain for each filter range.

1. Frequency-Tunable Hearing
Aid
Isaias Amaya
Osvaldo Rodriguez-Martinez
Otoniel Canuz
Duy Le

2. Goals
1. To build a frequency-tunable hearing aid based on gain op-amps
and frequency filters.
2. Allow the user to select the frequency range(s) that he/she needs
to be amplified more than the rest.

3. Specifications
1. Amplify the input signal by a factor of 100 in total (x10 for each op
amp.)
2. Generate a reference voltage VGND of ~1.65V in order to reduce
noise due to voltage fluctuations in GND.
3. Split the signal into 4 frequency ranges, allowing enough overlap in
the frequency bandgaps of the filters so that there would be no
frequency ranges left out
4. Set the gain of the PGAs according to the user-chosen settings in
the tuning stage.

5. Tasks
• Pre-amp, and Output Stages: Isaias Amaya
• Filters and Power Stage: Osvaldo Rodriguez-Martinez
• PGA and Arduino: Duy Le and Otoniel Canuz

6. Milestones
• Week of Oct 19:
• Analyze circuits, create plots, comprehend datasheets, comprehend code
• Start building Pre-Amp, Filters, Power, and Output Stages (without the ICs in place), start soldering ICs.
• Week of Oct 26:
• Have Pre-Amp, Filters, Power And Output Stages Built.
• Have code ready to launch on the Arduino, and all the wiring on the Arduino ready to plug when the other
stages are ready for integration.
• Integrate circuit
• Week of Nov 2:
• Test runs
• Measure outputs, making sure that:
• Power stage is setting the correct VGND value
• Signal is being amplified enough at pre-amp stage
• Signal is being split into 4 more-or-less non-overlapping frequency ranges at the filter stage
• PGAs are amplifying the correct frequency ranges, according to the settings in the Arduino
• Output is summing all outputs at unity.
• Week of Nov 9:
• Finish circuit, it must be operating at 100% capacity by the end of this week to not be feeling the pressure the
following, final week.
• Take our measurements, analysis, graphs, etc, and start putting together a presentation

7. Test Plan
1. Test the soldering of the LT6910 PGAs(SOT-23) and the
LT1632(SOIC-8) Op Amps.
2. Test that the total gain of the preamp stage is ~100
3. Test that the Arduino is generating a tone and the buttons are
receiving input from the user to in fact double the gain of each
frequency range.
4. Verify that the filters are attenuating the frequencies that each
filters is supposed to.

8. Demonstration
of Operation

10. PGA – 3-bit Digital Gain Truth Table
G2 G1 G0 Volts/Volts
0 0 0 0
0 0 1 -1
0 1 0 -2
0 1 1 -4
1 0 0 -8
1 0 1 -16
1 1 0 -32
1 1 1 -64

11. Analysis of Pre-
Amp and PGAs

12. Gain of
Pre-Amp
Stage OP1A

13. Gain of
Pre-Amp
Stage OP1B

14. Low Frequency-
Range Peak to
Peak Voltage
when user
settings are set to
unity gain for this
frequency range

15. Low Frequency-
Range Peak to
Peak Voltage
when user
settings are set to
x2 gain for this
frequency range

16. Analysis of
Filters

17. 1st filter(0-300[Hz]) analysis: Theoretical Bode Plot

18. Measured values
Input Voltage [mV] Frequency [Hz] Output Voltage [mV] Gain [dB]
15 50 94 15.9
15 100 175 21.3
15 200 255 24.6
15 300 285 25.57
15 400 295 25.8
15 500 300 26
15 600 300 26
15 800 290 25.7
15 1000 277 25.3
15 2000 215 23.1
15 3000 165 20.8

19. Bode Plot: Measured

20. Second Filter(300-3000[Hz]) Analysis:
Theoretical Bode Plot

21. Measured Values
Input Voltage [mV[ Frequency [Hz[ Output Voltage [mV] Gain [dB]
15 50 5 -9.5
15 150 70 13.3
15 300 100 16.4
15 500 250 24.4
15 700 305 26.16
15 900 323 26.6
15 1000 323 26.6
15 2000 250 24.4
15 2500 215 23
15 3000 190 22.05
15 4000 145 19.7
15 10000 65 12.7

22. Bode Plot: Measured Values

23. 3rd Filter(3-8[KHz] Analysis: Theoretical Bode
Plot

24. Measured Values
Input Voltage [mV] Frequency [Hz] Output Voltage [mV] Gain [db]
15 100 9 -4
15 200 100 16.4
15 400 235 23.9
15 600 332 26.9
15 800 332 26.9
15 1000 332 26.9
15 4000 310 26.3
15 6000 213 23.05
15 7000 185 21.82
15 9000 145 18.95
15 12000 113 15.5
15 20000 75 13.9

25. Bode Plot:Measured

26. 4th Filter(8+[KHz]) Analysis:

27. Measured Values
Input Voltage [mV] Frequency [mV] Output Voltage [mV] Gain [dB]
15 100 70 13.3
15 500 70 13.3
15 1000 70 13.3
15 2000 124 18.2
15 3000 150 20.1
15 5000 250 24.4
15 7000 300 26
15 9000 320 26.3
15 12000 330 26.8
15 20000 330 26.8
15 60000 320 26.5
15 100000 310 26.3

28. Bode Plot:Measured

29. Bode Plot:Measured