By Paul Shao
When solving a circuit design question on the exam, sometimes it might be very hard to wrap your head around how to come up with a well-designed and fully functional circuits that fulfill all the requirements. However, a quick trick that you can use to at least get a head start on the problem or head in the general right direction is to extract "keywords" from the problem and mapping it to a circuit component/configuration you already know. This set up will usually do at least 50% of the design for you, while what is left normally is just to figure out how to connect them together.
The table below lists a general mapping between the keywords you see within the question(s) and the corresponding circuit elements:
| Keywords | Circuit Elements/Concepts |
|---|---|
| amplify voltage | non-inverting op-amp |
| invert/reverse voltage | inverting op-amp |
| voltage/current change based on a given condition (such as applying a force or a change in temperature) | voltage divider (usually in this case the problem will provide you with a variable resistor that changes its resistance based on the given condition) |
| output two different voltages/currents based on a given condition (such as a changing the direction a bot is heading or turning a switch on or off) | op-amp comparator (be careful about what you feed into the V+ and V- parts of the comparator; remember that V+ is the input variable voltage, while V- is the reference voltage) |
| maintains a buffer against a high input voltage/provides stability against variable signals | op-amp buffer |
| provides a linear combination of the given voltages | KCL (consider how currents merge into one node as a sum of V/R's, essentially voltages multiplied by scalars); for more references, you can search up the term "summing amplifier" |
| provides the difference between the given voltages | differential amplifier (a combination of inverting and non- inverting amplifier. Voltage divider feeding into V+, and inverting amplifier with V- on top) |
| accumulate voltages -> store charges to be released in the next iteration / when a switch is turned on | connecting voltage source to a capacitor for storing charges to its full capacitance |