2. Tutorial: Mechanic - electrician Topic: Electronics II. Class Operational Amplifiers: Comparators – Part 1 - Basics Prepared by: Ing. Jaroslav Bernkopf Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

3. A comparator is a device that compares two voltages. Its output indicates which of the input voltages is larger. Comparators – Part 1 - Basics Operational Amplifiers 2 V out V i+ V i-

4. If the voltage on the non-inverting input (V i+ ) is higher than the other voltage (V i- ), the output voltage V out is positive. And vice versa: If V i+ is lower than V i-, the output voltage V out is negative. Comparators – Part 1 - Basics Operational Amplifiers 3 V out V i+ V i-

5. V out is positive, because V i+ is higher than V i-. Comparators – Part 1 - Basics Operational Amplifiers 4 V i- is higher than V i+ therefore V out is negative. V out V i+ V i-

6. Comparators – Part 1 - Basics Operational Amplifiers 5 Operational amplifiers as comparators – disadvantages 1)Operational amplifiers are slow. 2)Their output levels are not „logic“.

7. Comparators – Part 1 - Basics Operational Amplifiers 6 1)Operational amplifiers are slow. When a fast signal of a high frequency is applied to the inputs, an operational amplifier reacts too lazily. It needs a long time to wake up and then another long time to transit from one level to the other. V i- V out V i+

8. Comparators – Part 1 - Basics Operational Amplifiers 7 1)Operational amplifiers are slow. The output V out should start moving here – when V i+ becomes lower than V i-. But it starts more than 0.5μs later – here. And stops moving another 2.5 μs later – here. V i- V out V i+

9. Comparators – Part 1 - Basics Operational Amplifiers 8 The high level output voltage should have a „TTL“ value, i.e. +5 V maximum. Here it is about +13.5 V. The low level output voltage should be near to zero. Here it is about -13.5 V. V i- V out V i+ 2)Output levels of operational amplifiers are not „logic“.

10. Comparators – Part 1 - Basics Operational Amplifiers 9 V i+ V i- V out = ??? Complete the picture below. Suppose the extreme output voltages are ±13.5 V.

11. Comparators – Part 1 - Basics Operational Amplifiers 10 V i+ V i- V out

12. Comparators – Part 1 - Basics Operational Amplifiers 11  http://www.wikipedia.com http://www.wikipedia.com  http://www.thefreedictionary.com http://www.thefreedictionary.com  http://holbert.faculty.asu.edu/eee202/EEE202_Lect8_OperationalAmplifiers.ppt http://holbert.faculty.asu.edu/eee202/EEE202_Lect8_OperationalAmplifiers.ppt  http://www.wisc-online.com/Objects/ViewObject.aspx?ID=SSE2803 http://www.wisc-online.com/Objects/ViewObject.aspx?ID=SSE2803