How to identify the feedback topologies?
The problem is that from a term "Series-Shunt" it is not clear what comes first: "in" or "out"? I have discovered that different authors handle this subject differently. For this reason I prefer, for example: Voltage-controlled current feedback.
Examples:
- Voltage-controlled voltage feedback: Non-inverting opamp,
- Voltage-controlled current feedback: Inverting opamp,
- Current controlled voltage feedback: Common emitter stage with Re feedback,
- Current- controlled current feedback: (a) Inverting OTA amplifier, (b) common emitter stage with a voltage divider between collector and signal input (base node at the middle point).
Yes there is one easy way in which you can identify the topology. Just follow these steps.
- Identify the feedback network/element.
- If at output side, feedback is connected to the output of the circuit directly, name it as 'voltage', or else 'current'.
- If at input side, feedback is connected to the input given to the circuit directly, name it as 'shunt' or else 'series'.
Ex- if it comes out to be - voltage shunt feedback (named from output to input), you can also name it as shunt shunt feedback.
{at input side: shunt=current, series=voltage.
at output side: shunt=voltage, series=current }
Let me try to provide a intuitive way which i find very easy to understand
Voltage and Current leaves you with 4 possible combinations with which you can sample (at the output) and mix the feedback to input.
Now coming to sampling and mixing:-
Sampling:- At the output we take sample of what is there at output (since we want to check the behavior of output). Now we dont want to disturb the output when we take the sample. Thats why when voltage is sampled, its in parallel (since voltage is undivided in parallel) while current in series (current does not change in series). Very much like how we attach a multi meter to a circuit (we want the readings without affecting the setup)
Mixing:- Now on the mixing end we want to affect the signal that is provided to the amplifier, since that is the whole point of getting the feedback. So voltage will be in series and current will be in parallel (so that they can change the input and in effect change the output).
Series-Series ......Voltage in - Current out
Series-Shunt .......Voltage in - Voltage out
Shunt-Series .......Current in - Current out
Shunt-Shunt ........Current in - Voltage out
So i hope the above lines will make more sense to you.