Normally software deceive us when
they produce our intended output for the respective circuit using the
pre-programmed ideal power source. Real world is out of that myth and so it
provide us an obscure problem while implementing the same circuit in real domain.
Some thumb rules and imitations of others' solution may provide us quick and impermanent relief from our time consuming problem, but a little
understanding may clear the concept to solve the unclear and unattended
problem by ourselves. By having the last line in my mind I have tried to get
through the concepts of bypassing and decoupling by using lots of blogs,
papers, books, tutorials etc etc etc…
Both those fishes (bypassing and
decoupling) are not really as complex as I was pretending them. Here I am
trying to share some encapsulated knowledge about bypass capacitor and
decoupling capacitor which I’ve got separately from various sources.
This blog has been divided in
some parts….
Here is the first part – discussed about only one question; Why we
need bypassing? Or say this part is just a very basic introduction with a
problem, which needs a solution called Bypassing.
WHAT IS BYPASS? CAN’T I TRAVEL THROUGH IT RATHER THAN BYPASSING IT?
Definition:
Bypassing
is the reduction of high frequency current flow in a high impedance path by
shunting that path with a bypass, usually a capacitor. Bypassing is used to
reduce the noise current on power supply lines.
Yeah, I know that it was a
rocketed definition! So forget it… Yippee…..
Let’s have some talk, your eyes
are really beautiful… oh don’t be shy... I am just lying. Now concentrate on
your eyes behaviour!! When your eyes get focused to a highly brightened lights
obviously they will get smaller to provide you a tolerable vision… suppose you
want to scold me,
obviously and rudely the size of your eyes will get larger… Why?? Why?? Why??
It’s natural, by fluctuating the
size of your eyes you just wanted to satisfy your goal. A goal of being
compatible with your environment. Brighter light and related situations causes
the need of fluctuation in your eyes’ size otherwise our eyes may get a serious
damage. Similar kind of thing is happening with our circuit working in real
world (circuit implemented in simulator are in ideal case – we’ll not consider
them in our discussion).
In our circuits our DC supply are
also having/causing the same problem with which we should deal. First of all,
by relating our eyes with our batteries – similar to above section we’ll first
discuss about what problems our DC sources are having/causing.
We are using our batteries with
various kind of circuits – similar to eyes, which we’re using to see various
scenes having different brightness levels. In addition to that, our circuits
are mostly not consuming current with constant rate – similar to eyes, which
are not experiencing the similar brightness level whole the day/life.
(You may ask here that – What if
my circuit is consuming current at constant rate???
My answer is – Please have some patience we’ll talk about it later.)
My answer is – Please have some patience we’ll talk about it later.)
(Now, you may ask another
question that – Why so most of our circuits are not consuming current with
constant rate??
Answer is – In practice, controllers/ Digital ICs/ and all other mostly used components are switching their states as per the input, means the flow of electron through them is not constant for all the time – it depends on their current state (on/off), heat dissipation, and so many other factors which are force to believe that circuit/load is not demanding current at constant rate. In fact, sometimes it is higher or otherwise go below than an average.)
Answer is – In practice, controllers/ Digital ICs/ and all other mostly used components are switching their states as per the input, means the flow of electron through them is not constant for all the time – it depends on their current state (on/off), heat dissipation, and so many other factors which are force to believe that circuit/load is not demanding current at constant rate. In fact, sometimes it is higher or otherwise go below than an average.)
Now, let me summarize what we
have gone through about. We’re using DC Batteries/ AC to DC converters/
Adapters/ Rectifiers/ Voltage regulators to provide DC supply to our circuits and
these circuits normally are not consuming current with constant rate. In
practice, most digital circuits as well as circuits which provides analogue
output works with DC power source.
Now let come back to some talk.
Variation in brightness level is the problem which cause the change in the size
of our eyes. Similarly, variation in current consumption by circuits/load cause
the change in the voltage drop across the load/circuit (I am assuming that you know V = IR).
But we’re intended to provide a
constant voltage drop to our load/circuit. For example, 3.3V to a controller
should not be vary excessively with time. But controller is asking for the
current rate which fluctuates from 100 mA to 300 mA (just an example) and so
the voltage drop across the controller will also tend to vary about 3.28V to
3.33V (just an example). Below is the graph yielding similar kind of scenario
for 5V DC supply against time.
So now, we are clear about the
problem which we need to solve. The problem is the fluctuation in voltage
provided to our load/circuit. So let’s heading towards the solution. We need to minimize this fluctuations ANY HOW.
An Engineering mind may analyze
the problem and can come with the possible list of solution, here are some
options which may solve this problem.
i)
We can ask to our circuit/load not to consume
current varyingly.
- For that we need to build components which do
not change their current consumption with time – seems not a practical
solution.
ii)
We can ask to our source to provide current
varyingly but not to change the voltage drop.
- Mr Georg
Simon Ohm may not forgive us for thinking about this.
iii) We can add a 3rd party between source
and load who do not disturbs the current consumption made by the load and also
do not let the voltage drop vary.
- Hmmmm…… But how we can do it??? Is there any
component available who do not disturbs the DC Current and also can banned the
voltage fluctuations????
-
If we consider voltage fluctuation as an
analogue signal, then we can say that – we’re in need of a thing which works
differently to DC and AC signals… Oh!!!! Yeah…. You got it??? Really???? Hmmm…
you’re right. We’ve two components which works differently for both DC and AC.
The first is Inductor and the second is Capacitor.
- Phewww…. We get it… at last.
Now, in this part we’re done with the very basic
introduction with the problem statement – here we can’t expect to solve the
definition of Bypass (so that is still suspense).
In the next parts we’ll
discuss on…
Out of this two (Capacitor and Inductor) what to use?
Post mortem of the definition of bypassing.
How to use the solution?
When to use?
How it works?
How efficient this solution is?
How to make this solution more efficient?
Why it is called bypassing? Etc…
Post mortem of the definition of bypassing.
How to use the solution?
When to use?
How it works?
How efficient this solution is?
How to make this solution more efficient?
Why it is called bypassing? Etc…
