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/ je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.
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-
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-
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-
Comparators – Part 1 - Basics Operational Amplifiers 5 Operational amplifiers as comparators – disadvantages 1)Operational amplifiers are slow. 2)Their output levels are not „logic“.
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+
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+
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 V. The low level output voltage should be near to zero. Here it is about V. V i- V out V i+ 2)Output levels of operational amplifiers are not „logic“.
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.
Comparators – Part 1 - Basics Operational Amplifiers 10 V i+ V i- V out
Comparators – Part 1 - Basics Operational Amplifiers 11