====== Block 24 — Wrap-up and Applications ======

===== Learning objectives =====
<callout>
After this 90-minute block, you can
  * connect the different negative-feedback op-amp circuits (Blocks 21–23) into a coherent system view.
  * explain how negative feedback determines gain, impedance, and linearity in practical op-amp circuits.
  * select an appropriate op-amp circuit (buffer, amplifier, summing, differential, transimpedance, transconductance) for a given application.
  * analyze complete signal chains consisting of several op-amp stages.
  * recognize practical limitations of real op-amp circuits (supply rails, saturation, loading, offsets).
  * interpret op-amp circuits as signal converters (voltage–voltage, current–voltage, voltage–current).
</callout>


===== Conceptual overview =====
<callout icon="fa fa-lightbulb-o" color="blue">
  * All op-amp circuits in Blocks 21–23 are variations of one single idea: \\
    a high-gain amplifier whose output is fed back in a controlled way.
  * Negative feedback forces the differential input voltage $U_{\rm D}$ to become very small, which makes the circuit behavior depend almost entirely on external components, not on the op-amp itself.
  * Resistors do not merely “limit current” here — they define signal relationships (ratios, sums, differences).
  * Many circuits that look different (buffer, amplifier, converter) are mathematically and conceptually closely related.
  * Thinking in terms of signal flow and conversion is the key step from circuit theory to real engineering applications.
</callout>

===== Core content =====

==== From individual circuits to a system ====

In [[Block21]], [[Block22]] and [[Block23]], several op-amp circuits were introduced one by one.
At first glance, these circuits may appear unrelated. \\ However, they can all be understood as special cases of the same feedback principle.

A practical electronic system rarely uses just one op-amp stage. Instead, several stages are cascaded, each fulfilling a specific role:

  * Input stage: impedance matching (voltage follower).
  * Scaling stage: amplification or attenuation (inverting / non-inverting).
  * Combination stage: summing or subtraction (summing / differential amplifier).
  * Interface stage: signal conversion (current–voltage or voltage–current).

Understanding why each stage is used is more important than memorizing formulas.

==== Negative feedback as an engineering tool ====

Negative feedback provides three essential properties simultaneously:

  * **Defined gain** \\ The closed-loop gain depends on resistor ratios, not on $A_{\rm D}$. \\ \\
  * **Stability and linearity** \\ Small nonlinearities inside the op-amp are strongly suppressed. \\ \\
  * **Impedance shaping** \\ High input resistance and low output resistance can be achieved at the system level.

These properties explain why op-amps are ubiquitous in analog electronics.

==== Typical application patterns ====

Some recurring patterns appear across many applications:

  * **Sensor readout** \\ Sensors often deliver currents or small voltages → transimpedance amplifier → voltage amplifier. \\ \\
  * **Signal conditioning** \\ Offset removal and scaling → differential amplifier + non-inverting amplifier. \\ \\
  * **Summation and mixing** \\ Multiple signals combined with weighting → summing amplifier. \\ \\
  * **Actuator drive** \\ Voltage command converted into controlled current → voltage-to-current converter.

Recognizing these patterns allows fast interpretation of unfamiliar circuits.