# In electronics, why do we need a two port network?

1. Aug 17, 2014

### meisnkp

Why do we need a two port network? Is there something which a one port network lacks? Why we needed a two port network connection?

2. Aug 17, 2014

### Simon Bridge

Welcome to PF;
What a 1-port network lacks is a second port.
The second port on the input and the output allows for more complicated arrangements of components.
Almost all electronics devices would not function with only one port.
For instance - how do make an amplifier with only one port? How do you add a power supply with only one port?
(Note: the ground can be the second port.)

3. Aug 17, 2014

### meisnkp

Hmm...thanks

4. Aug 17, 2014

### meisnkp

But what about the two port circuits with only simple linear resistances (and not any non-linear elements like transistor s)? What's special in that?

5. Aug 17, 2014

### sophiecentaur

I am not sure about that. Ifaikr, a 'port' consists of two terminals - e.g between an input terminal and ground or two input connections. A two port device would have four terminals or possibly three terminals with one 'common', which may or may not be 'ground'. I don't think the power supply connections are classed as ports in an active device.

A single port network would just have two terminals - such as a resistor (the simplest), an RC or RLC network or a more complicated circuit that might even be active.

We "need" two port networks if we want to have all those functions that amplifiers, transformers and matching networks provide.

6. Aug 17, 2014

### davenn

yes agreed ... a port is an I/O type port input only, output only, or bi directional
and may be considered analog or digital

Dave

7. Sep 7, 2014

### jsgruszynski

A one port models a single 2-terminal circuit element.

A two port models a transfer function or similar system component as wells ladder and tee circuit elements. Dependent sources, for example, are 2-ports. A transfer function of the form y = A x is a 2-port.

Since transfer functions are extremely common it's nice to have a very generic linear circuit model concept for them.