Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 Anglicky v odborných předmětech "Support of teaching technical subjects in English“ Tutorial: Mechanic - electrician Topic: Electronics II. Class Operational Amplifiers: Comparators – Part 1 - Basics Prepared by: Ing. Jaroslav Bernkopf AVOP-ELEKTRO-Ber-010 Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

Vi+ Vout Vi- A comparator is a device that compares two voltages. Comparators – Part 1 - Basics Definition A comparator is a device that compares two voltages. Its output indicates which of the input voltages is larger. Vout Vi+ Vi- Operational Amplifiers

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

Vout Vout is positive, because Vi+ is higher than Vi-. Vi- Vi- Comparators – Part 1 - Basics Description Vout Vout is positive, because Vi+ is higher than Vi-. Vi- is higher than Vi+ therefore Vout is negative. Vi- Vi+ Operational Amplifiers

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

Operational amplifiers are slow. Comparators – Part 1 - Basics Description 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. Vout Vi+ Vi- Operational Amplifiers

Operational amplifiers are slow. Comparators – Part 1 - Basics Description Operational amplifiers are slow. The output Vout should start moving here – when Vi+ becomes lower than Vi-. But it starts more than 0.5μs later – here. And stops moving another 2.5 μs later – here. Vout Vi+ Vi- Operational Amplifiers

Output levels of operational amplifiers are not „logic“. Comparators – Part 1 - Basics Description Output levels of operational amplifiers are not „logic“. 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. Vout Vi+ Vi- Operational Amplifiers

Comparators – Part 1 - Basics Task Complete the picture below. Suppose the extreme output voltages are ±13.5 V. Vi+ Vi- Vout = ??? Operational Amplifiers

Vi+ Vi- Vout Solution Comparators – Part 1 - Basics Operational Amplifiers

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