Design Build Measure package 1

1. Introduction

Goals

  • Practice the mechanics of analyzing BJT circuits at DC and confirming the results by matching hand analysis, simulation, and measurements of the same circuit.

  • Become familiar with the expectations for a “DBM package” submission.

Objectives

  • Focus on the boundaries where the transistor changes modes, and understanding how to directly solve for these points.

  • Solve a BJT circuit at DC while varying independent sources.

  • Setup and run LTspice and CircuitLab DC operating point simulations.

  • Construct and measure a (real) circuit’s DC operating conditions.

  • Assemble work of various forms into a coherent report focused on the stated goal.

2. Elements

hand analysis

day02 — hand analysis using reasonable assumptions, such as VBE=0.6 V and β=100.

simulation

Both LTspice and CircuitLab simulation. Examples of using these were in day03 and day09.

physical build and measurements

lab1

3. Submission format

These design-build-measure[1] packages are for you to learn how to self-check your own work by using alternate routes that theoretically yield the same “answer.” When all three paths end with the same results to within tolerances that are small enough, then you have shown yourself that you got it right.

The model of an instructor checking your work for correctness, including you never fixing the errors afterwards, is a traditional school thing. THE REST OF SOCIETY DOES NOT WORK THIS WAY. The closest a working engineer gets to this operating mode is in design or code review activies: a co-worker checks a unit of work for correctness and provides feedback of various types.

What does this mean for the deliverable for this course?

In a real way, the format of your submission is part of your decision to make.

Decisions, decisions
worriedface


  • What demonstrates your completion of the objectives that are part of the stated goals?

The answer to this question is what your submission should look like. There are many typical and creative ways to do this, do something you consider reasonable.

3.1. Suggestion

Contrast

  • suggest : to mention an idea, possible plan, or action for other people to consider

  • dictate : to tell someone exactly what they must do

Consider the three elements of this DBM package:

  • The hand calculations of day02 were in a series of three tables.

  • The measurements of lab1 also generated a series of data tables.

  • Both simulators can export their simulation data as text files for import into other software.

What if you plotted all three sets of data for a given value of RC on the same plot, using different colors and marker shapes for each set?[2] If those points were all nearly (vertically) coincident at the various values of VB, then this does indeed show that the four sets of data show the same thing!

After you make this “money figure”, then describe where each of the four sets of data came from. Here, this is your hand calculations, lab measurements, and two different simulators.

Show relevant things like

  • example hand calculation, at least one for each of the three transistor operation modes, since the circuit math is different for each,

  • the two simulation schematics,

  • a description and schematic of how you setup and took the lab measurements.

It would seem natural to assemble all of these pieces into a Google Doc or Microsoft Word document — something that can interleave figures, tables, and text.

Then take a step back and look over this assembled thing as someone reading this for the first time would (assume they have the requisite background knowledge, just not the details of this particular activity).

  • NEVER let the reader finish reading and have their first comment be: what even was the purpose of this thing?

  • Start the document with the stated goals of dbm01,

  • proceed to display evidence of reaching each of the objectives,

  • and briefly summarize the situation and some lessons-learned.

  • The reader should be able to easily agree that your concluding claims were in fact true based on the rest of the document.

Then submit this thing, perhaps with a ZIP file of relevant supporting files, to Blackboard!

But, how long or detailed should this be?

Submit and you will get feedback!

  • If too detailed, I’ll say which parts are more than I’m looking for. Then you’ll know to spend less time on those bits next time.

  • If too sparse, I’ll say which parts are missing something. Then you’ll get to improve them and submit again.[3]

4. What is Good Enough?

Determining “good enough” is an engineering skill unto itself — it depends on the purpose and situation.

Table 1. Tolerances of ECE standard parts stock
Type Tol.

resistors - ¼ W

±5 %

capacitors - electrolytic

±20 %

capacitors - polyester film

±10 %

capacitors - C0G ceramic

±10 %

capacitors - X7R ceramic

±10 %

inductors - toroidal

±15 %

inductors - solenoid

±10 %
1. There will be more of a real design element as we progress.
2. I like to use data markers with NO lines for points that are measured (you didn’t actually measure at the points in between) and use solid lines with NO markers for things like simulation sweeps where the curves are continuous.
3. Maybe with a 1-resubmission limit?