Dies ist eine alte Version des Dokuments!

Block 23 — Comparator Circuits

Learning objectives

Preparation at Home

Well, again

• read through the present chapter and write down anything you did not understand.
• Also here, there are some clips for more clarification under 'Embedded resources' (check the text above/below, sometimes only part of the clip is interesting).

For checking your understanding please do the following exercises:

• …

90-minute plan

1. Warm-up (x min):
   1. ….
2. Core concepts & derivations (x min):
   1. …
3. Practice (x min): …
4. Wrap-up (x min): Summary box; common pitfalls checklist.

Conceptual overview

Core content

Comparator

Up to now we focussed on operational amplifier, which is only usable in a closed-loop setup. However, it also as a „special brother“, the comparator.
The differences form the comparator in contrast to the operational amplifier are:

1. It is only used in positive feedback. It should never be used in negative feedback.
2. It is optimized for fast switching
3. It only outputs in saturation, which means it only has two possible outputs, see details below.

The symbol is related to the op-amps triangular shape - often the exact same symbol is used.

So, but what is the output, now? For this, it helps to have a look onto the simulation below.
There are two types of comparators:

1. comparators with open-collector output:
   This type outputs the minimum value, when the non-inverted input is bigger than the inverted one.
   Otherwise, the output is high-ohmic or undefined.
   This is sometimes shown by a diamond shape ◇ on the output.
   $$U_{\rm O,OC}= \biggl\{ \begin{array}{l} &&\text{undefined} &&\text{for} &&U_{\rm I,1}>U_{\rm I,2}\\ &&U_{\rm sat, min} &&\text{for} &&U_{\rm I,1}<U_{\rm I,2} \end{array}$$
2. comparators with push-pull output:
   This type outputs the minimum value, when the non-inverted input is bigger than the inverted one.
   Otherwise, it outputs the maximum value.
   $$U_{\rm O, PP}= \biggl\{ \begin{array}{l} &&U_{\rm sat, max} &&\text{for} &&U_{\rm I,1}>U_{\rm I,2}\\ &&U_{\rm sat, min} &&\text{for} &&U_{\rm I,1}<U_{\rm I,2} \end{array}$$

Common pitfalls

• …

Exercises

Worked examples

…

Embedded resources