What is Electronic circuit?
An electronic circuit is a complete course of conductors through which current can travel. Circuits provide a path for current to flow. To be a circuit, this path must start and end at the same point. In other words, a circuit must form a loop. An electronic circuit and an electrical circuit have the same definition, but electronic circuits tend to be low voltage circuits.
For example, a simple circuit may include two components: a battery and a lamp. The circuit allows current to flow from the battery to the lamp, through the lamp, then back to the battery. Thus, the circuit forms a complete loop.
What are Active Electronic Components?
Active electronic components are those that can control flow of electricity
Example: Transistors, Integrated Circuits or ICs, Logic Gates, etc.
What are Passive Electronic Components?
Passive components are those that do not have gain or directionality. They are also called Electrical elements or electrical components.
Example: Resistors, Capacitors, Diodes, Inductors.
Types of Electronic Circuit
A circuit can of following types:
1. Analog Electronic Circuit
Analog electronic circuit are those in which signals may vary continuously with time to correspond to the information being represented.
Example: Electronic Equipment like voltage amplifiers, power amplifiers, tuning circuits, radios, and televisions are mainly analog.
2. Digital Circuit
A digital circuit is a circuit where the signal is either of the two discrete levels – ON / OFF or 0 / 1 or True / False. Transistors are used to create logic gates perform Boolean logic.
Example: Multiplexers, De-multiplexers, Encoders, Decoders, Counter, Flip-Flop
3. Mixed-Signal Circuit
Mixed-Signal Circuit, are also called hybrid circuits, contain elements and properties of both Analog Circuit and Digital Circuit.
 Examples: Comparators, Timers, PLLs, ADCs (Analog-to-Cigital Converters), and DACs (Digital-to-Analog Converters).