Diary of a Trainee Electronics Engineer: May 2018
Understanding the importance of impedance matching tracks on electronic circuits
This month I’ve watched my siblings start to look at picking their year nine options, which decide the subjects they will take at GCSE. It feels like I lifetime ago since I myself was making this choice, but in the process, I reminisced about what I did and my GCSE physics coursework sprung to mind.
Over the two years of my GCSEs this was the first time I was ever introduced to anything to do with electronics as we encountered simple circuits with a battery, resistor and an LED, and then moved on to understanding one of the most fundamental electronics equations to date – Ohms Law. As we were introduced to our coursework topic we discovered this was to do with investigating the change in resistance on a piece of wire; by altering either the gauge (thickness) or length of a piece of wire and then analysing the effects this had on resistance.
As I have progressed in my electronics career I have become to realise the importance of impedance matching circuits, and thinking back to my GCSE coursework I realised how important this was by understanding how resistance changes depending upon the area.
For old times’ sake, I decided to repeat this experiment by changing the length of some single core insulated wire and then making note of the resistance. As I did at GCSE I repeated each measurement three times to be sure to check for any anomalous results.
Table of results
Using the wire, I measured it to length and stripped 5mm of insulation from each end connected a multimeter. After taking measurements and taking the average I plotted a graph and the trend is obviously clear – the resistance increases proportionally with length.
This is exactly what we would expect to see as the further the electrons have to travel the more collisions happen, therefore the resistance increases as the length of the material does.
From the measurements alone, we can see this even though the increase in resistance is minimal, it is still there. Had much longer lengths of wire been used, I am certain that this would be greater.
Early in my electronics career, I didn’t really consider the effects of the resistance in the tracks/wires in circuits, however, as I get further into my career I’m beginning to understand the importance of this.
When we take into account the effects of the resistance in the tracks and the effect it has on the components/output of the circuit we call this impedance matching. This is the practice of designing input/output impedance in a way which it maximises power transfer and minimises signal reflection from the load.
Often, we require the load to match the impedance of the transmission line - i.e. ZOut = Zin – if this is achieved it can be considered a perfect match. This is especially important when dealing with high-frequency circuits or circuits which have more sensitive components, such as flip-flops.
Over the next few months, I’m going to spend more time looking at the many different applications of impedance matching and also other design techniques which maximise the performance of a circuit.