Your task is to design, build, and test an amplifier for an ultrasonic receiver which can detect a signal from at least 2 meters away.
1. Description
 Required decisions


How much voltage gain is enough?

Which op amp to use?

How many amplifier stages?

Some of these questions can only be addressed with thoughtful experimentation.
 General task order


Use WaveForms and your AD2 to measure the impedance versus frequency of your sensor.

Begin with a 1 kΩ reference resistor.

See this for instructions on using this feature: Using the Impedance Analyzer

Estimate the resonance frequency of your device from these measurements and determine whether this is a 24 kHz or 40 kHz unit.


Draw the schematic of a 1stage amplifier, including the sensor.

Use a voltage gain of 100 V/V.

Select an opamp from the available list which can amplify this signal.

Don’t forget to deal with DC offset voltage and input bias current issues in your circuit!


Build this prototype amplifier.

Measure the voltage gain at the signal frequency, it should match your prediction.

Measure the signal output magnitude for at least one known distance from the transmitter. Use 0.5 to 1.0 meter distance for convenience.


Compute the gain required for a reasonable output amplitude for a distance of 2 meters.

Design a multiplestage amplifier schematic which achieves this gain. Incorporate things you learned from the first amplifier’s testing.

Build and measure!

2. Helpful information
2.1. Inverse square law
Consider a finite amount of sound intensity (power per area, W/m^{2}) leaving a speaker and a virtual sphere of diameter d centered at the speaker having a small patch on it which collects all energy pasing through the patch’s area. See Inverse square law setup for an illustration. A certain fraction of the total sound power emitted from the speaker will be absorbed by the patch depending on the proportion of the patch’s area to the sphere’s total surface area.
If the patch’s distance is doubled to 2d, the patch’s area must be increased by a factor of \(\left(\frac{2d}{d}\right)^2\) (4x) in order to absorb the same power as before. Stated the other way, a (same area) patch at distance d_{2} will absorb the following power compared with a patch at distance d_{1}:
Since the voltage output of the microphone is proportional to the square root of the power, the relationship may also be expressed as:
→ Doubling of distance reduces received power by 1/4 and a reduction in received voltage by a factor of 1/2.
2.2. 1pole RC highpass filter:
2.3. 1pole RC lowpass filter:
2.4. DC errors
If you make the following assumptions:

The openloop gain A_{v0} is large enough, which means \(\gg \left(1 + \frac{R_f}{R_1}\right)\)

The opamp’s openloop output impedance Z_{out} is low enough, or much less than the impedance seen by the output node (for this lab = 50,047 Ω).
The total noninverting opamp output from the input signal and DC errors V_{OS} and (I_{B}, I_{OS}) ←→ (I_{B+}, I_{B}) is:

\(R_{eq+}\) and \(R_{eq}\) are the impedances seen by the + and  input terminals of the opamp.
3. References

[341notes] D. White, ECE 341 Class notes 2018 folder, https://drive.google.com/folderview?id=1hUN1Xicpr9tpCsL2937jfNaCxgpyLT3L

[341docs] D. White, ECE 341 reference documents folder, https://drive.google.com/folderview?id=0B5O5cSaA0tEQYVpaSnJxMGFrdHM

[AoE] P. Horowitz and W. Hill, The Art of Electronics, 3rd ed. Cambridge University Press, 2015. https://artofelectronics.net

[LAoE] T. Hayes, Learning the Art of Electronics: A HandsOn Lab Course, Cambridge University Press, 2016. https://learningtheartofelectronics.com

[LEC] Tony R. Kuphaldt, Lessons in Electric Circuits, Source version: https://www.ibiblio.org/kuphaldt/electricCircuits/, All About Circuits version: https://www.allaboutcircuits.com/textbook/

[CLbook] Michael F. Robbins, CircuitLab, Ultimate Electronics: Practical Circuit Design and Analysis, https://www.circuitlab.com/textbook/

[TCA] Alfred D. Gronner, Transistor Circuit Analysis, Simon & Schuster, 1970, https://archive.org/details/TransistorCircuitAnalysis

[] Neil Weste and David Harris, CMOS VLSI Design  A Circuit and Systems Perspective, 4th edition. AddisonWesley, 2011. http://pages.hmc.edu/harris/cmosvlsi/4e/index.html

[Guidebook] D. White, Guidebook for Electronics II. https://agnd.net/valpo/341/guidebook

[] H.K. Gummel, H.C. Poon, An Integral Charge Control Model of Bipolar Transistors. Bell System Technical Journal, 49: 5. MayJune 1970 pp 827852. https://archive.org/details/bstj495827

[ROHM] ROHM Semiconductor, Electronics Basics, http://www.rohm.com/web/global/en_index

[vishayeseries] Vishay, Standard Series Values in a Decade for Resistances and Capacitances, https://www.vishay.com/docs/28372/eseries.pdf