Basic Electronics

Understanding how to calculate voltage drop across a resistor is very fundamental for anyone who is into electronics or electrical engineering. In this step-by-step guide, we will break down the process, making it accessible and very simple even for beginners. By the end, you’ll have a solid grasp of this crucial concept, enabling you to analyze, solve and design circuits with confidence.

Before that let’s brush up the concept of Ohm’s law:

• A common way to show the behavior of a circuit device is it’s characteristic.
• 
  This is a graph of the current “I” through the device as a function of applied voltage “V” across it. This device, the resistor, has the simple linear V– I characteristic shown in fig. above.
• This linear relationship of the device is expressed by Ohm’s Law:
  V = IR
• Here, the constant of proportionality R, is known as the resistance of the device and is equal to the slope of the I–V characteristic. The unit of resistance is ohm, the symbol is Ω. Any device with a linear VI characteristic could be treat as resistive in nature.

What is the voltage drop across a resistor?

• The voltage drop across a resistor is nothing but the voltage value across a resistor. Sometimes it is also called ‘voltage over the resistor’ or simply ‘Voltage drop’.
• It is generally indicated as: ‘V(drop)‘ or ‘Vr’ or  ‘Vd’
  For multiple resistors, it is written as Vr1, Vr2, Vr3, and so on.

As we all know, a resistor is a device that offers resistance to the current flowing through it. Then, by applying Ohm’s law, the resistor will offer a voltage drop across a resistive device and it is given as:

 V(drop) = I × R

where,

I = current through the resistor in (A) ampere
R = resistance in (Ω) ohms
V(drop) = voltage drop in (V) volts

How to calculate voltage drop over resistance step-wise :

Step1: Simplify the given circuit. If the circuit is full of resistors in series and parallel, then rearrange the resistors to make it appear simple connections. (check the practical example below)

Step2: Then, find the equivalent resistance.

For parallel use this formula: 1 / Req. = 1 / R1 + 1 / R2 …
And for series use this: Req. = R1 + R2 + . . .

Step3: Find the current through each resistor. (Current through the series resistor is same and current through the parallel resistors is different and depends on its value)

Step4: Apply the formula from Ohm’s law to calculate voltage drop, V=IR

One way is to check this link –> Voltage Drop Across Resistor Calculator online tool.

There is also another way to find the voltage drop, simply you can calculate it by using Voltage Divider Formula

The voltage across series circuit- Practical examples:

Case I:

If there is only one resistor in series with a battery or a power supply as shown in this circuit.

In this circuit, the voltage drop across the resistor is the same as that of power supply. This is because both the components have common potential points shared between them (point A & point B)

∴Vs = Vdrop = 5 volts (say)

Case II:

If there are two or more resistors in series with a battery as shown in this circuit.

In this circuit, we have to calculate the total current ‘I’ through the circuit.
I (total) = V(supply) / R(equivalent)

∴ I(total) = 5 / 30 =0.166 A

Then, the Voltage drop across R1 will be: Vr1 = I × R1
The voltage drop across R2 will be: Vr2 = I × R2
Also, voltage drop across Rn will be: Vrn = I × Rn

—> Vr1 =I × R1 = 0.166 × 10 =1.66 volts  &  Vr2 = I × R2 = 0.166 × 20 = 3.33 volts

The voltage across parallel resistors:

Case I:
There are two resistors in parallel with a battery or a power supply as shown in this circuit.

In this circuit, the voltage drop across these parallel resistors is the same as that of power supply.
This is because both the resistors have common potential points shared between them (point A & point B), so the voltage will be the same but the current will be different.

∴Vs = Vdrop = Vr1 = Vr2 = 5 volts  (say)

Case II:
There is one resistor in series and two resistors with a power supply as shown in this circuit.

In this circuit, we need to calculate the current ‘I’ through each component.

• i1 = I (total) = Is  = V(supply) / R(equivalent)
  Here, R(equivalent) = R1 + Rp,
  Also, 1 / Rp = 1 / R2 + 1 / R3∴ Rp = 12Ω  &  R(equivalent) = 22Ω

   

• i2 = i1 * (R3/(R2+R3))
  i3 = i1 * (R2/(R2+R3))

• The Voltage drop across R1 will be Vr1 = R1 * i1
  A voltage drop across R2 will be Vr2 = R2 * i2
  Voltage drop across R3 will be Vr3 = R2 * i3

Putting values we get,

Now, i1 = V(supply) / R(equivalent) = 5 /22 = 0.227 amps
∴ i1 = 0.227 A

Voltage drop across 10 ohm -> Vr1 = 10 * i1 = 10 × 0.227  volts
∴ Vr1 = 2.27 volts

Now, i2 = i1 * (R3/(R1+R2))
∴ i2 = 0.1362 A 

Voltage drop across 20 ohm -> Vr2 = 20 * i2 = 20 × 0.1362 volts
∴ Vr2 = 2.724 volts

Now, i3 = i1 * (R2/(R1+R2))
∴  i3 =0.09 A

Voltage drop across 30 ohm -> Vr2 = 30 * i2 = 30 × 0.09 volts
∴ Vr3 = 2.7 volts

Method 2:

• Find i1 = V(supply) / R(equivalent) = 0.227 A
  Then,Voltage drop across R1 will be Vr1 = R1 * i1 = 10 × 0.227 = 2.27 volts
  ∴ Equivalent voltage at point ‘A’ will be equals to Veq = Va = Vs – Vr1
  ∴ Va = 5 – 2.27 = 2.73 volts
  Therefore, we get equal potential value across R2 & R3.
• Thus, Va = Vr2 = Vr3 = 2.73 volts

Method 3:

In this method, we use a digital multi-meter or you can say a voltmeter. All you need is to set the multi-meter to voltage mode.
Now using its 2 probes check the voltage across the required resistor by connecting probes across it. (in fig. voltmeter reading is for indications only)

Voila !! You got it.

This is the easiest way to find a voltage drop across resistor in any circuit.

Voltage divider rule is one of the most common concept in electronic circuit design. So today we will be discussing in detail the voltage divider formula from where it comes from where the formula is derived along with some practical example. Also mentioned how to design voltage divider circuit for the required output.

While going though electronics basics we face a lots of difficulties learning the formulas, the rules and steps to implement them. But, below topics covered the easy method to learn formulae along with the tricks to remember it.

What is voltage divider rule?

Voltage divider rule is also called as potential divider rule or potential division rule or voltage division rule.
In short, it is assigned as VDR.

Voltage divider rules give the insight of the schematic circuit diagram and applicable formula and its derivation to help with different voltage requirement in the circuit designing.

Voltage divider definition :

> It is defined as the circuit which is used to reduce the large value of the voltage to the smaller value.
> Voltage divider circuit gives the required output voltage as a fraction of input voltage which can be manipulated using formula.
> A voltage divider circuit is a circuit that divides the single voltage value to the multiple output values.

The Voltage Divider is Passive in nature (as it has no active elements) and behavior is Linear (as output is linearly proportional to input)

Voltage divider schematics circuit:

Fig(a), Fig(b) & Fig(c) are voltage divider circuit diagrams.

The image showing three circuits below, they might appear different but fundamentally the same. They are only one circuit with different arrangements and source symbol. Simplifying them you will end up concluding that they are same in electrical rules.

Analysis and Voltage Divider Rule formula:

Figure showing a Basic diagram of voltage divider circuit which has two resistors. This is the basic circuit diagram that shows the VDR and its formula. This is very basic circuit and the formula is used for the calculating the output voltage allover while analyzing the circuits.

There voltage divider rule fits in the same concept as Voltage Drop Across Resistor check here!

Voltage divider rule proof and derivation:

Here, voltage supply is V is connected in series with resistor r1 and r2.

And current ‘i’ is flowing though them causing a voltage drop of v1 across r1 and voltage drop of v2 across r2.
As this is a closed-loop, the current flowing though it will be the same.

For deriving output voltage formulae we need to apply Ohms law across each resistor and the putting the values in equation obtained by KCL (Kirchhoff’s Current Law) as shown below step by step:

According to Ohm’s law we get,
v1 = i☓r1 ———-(I)
v2 = i☓r2 ———–(II)

Applying KVL in the above circuit
V – v1 – v2 =0
ie, V = v1 + v2

By putting the value of v1 & v2 in above equation,
we get,
V = i☓r1 + i☓r2
∴ V= i☓( r1 + r2)

Hence,
i =V / (r1+ r2)

Substituting the value of “i” in (I) and (II)
we get,
v1 = r1☓(V / (r1+ r2))
v2 = r2☓(V / (r1+ r2))

(by adjusting the variables)
Also,
v1 = V☓(r1 / (r1+ r2))
v2 = V☓(r2 / (r1+ r2))   →(note: v2 = Vout)  →(III)

(by adjusting the variables for the conditions where we need to find the values of resistors)
Again,
r1 = (v1☓(r1+ r2)) / V
r2 = (v2☓(r1+ r2)) / V

[note: the above formula is very important and has its applications in designing voltage divider circuit]

To be Concluded :

• From equation →(III) we can say that the output voltage is equal to a voltage drop across output resistor (the resistor across which we are taking output)
  (check the circuit with 3 resistor in series you will get the point)
• The values of the resistor at denominator is nothing but the equivalent resistor of r1 and r2, it can be r1+r2+r3+…+rn, where n number of resistors.

Figure showing voltage divider with 3 resister and its equivalents:

In this circuit (as per the above conclusion from derivations):

→As in Fig. 1 Vout1 is the voltage across resistor R2 and R3

∴equivalent series resistanceR2 and R3 are taken.

→In the Fig. 1, Vout2 is the voltage across resistor R3 only.
Therefore, the equivalent series resistance R3 is taken.

For Fig. 1(a)

For Fig. 1(b)

The practical example of voltage divider circuit (VDR):

Q. Design a voltage divider to give the output voltage of 1.5 volts for designing an amplifier biasing. The given source voltage is 5V.

Ans.
Given→Vo= 1.5V & Vin= 5V
from eq→(III) or simplified formula(look for 1st image of the post)

we have, Vo= Vin.(R2/(R1+R2))

Assuming, R1= 1KΩ
and putting all the values in the formula,
1.5= 5.(R2/(1K+R2))
We get, R2= 0.428KΩ

Q. Design a voltage divider to give the different output voltage of 3 volt and 6 volts for the comparator, given that the input voltage source is having a potential difference of 9 volts.

Ans.
As equal resistor in series offers Equal voltage drop across each resistor.
∴ according to the question,

Vin= 9 Volts, Vout1= 6Volts and Vout2= 3Volts

From this, we can conclude that the smallest output is 3volts and another required output voltage is 6 volts.
Then, we can use three resistor of same values.(say 1kΩ)
∴ R1= R2= R3 = 1kΩ design is completed.

Q. Design a voltage divider to give the output voltage equal to half of the input. The given source voltage is 12V.

Ans.
Given→Vo= 1/2Vin & Vin= 12V

using the simplified formula:
we have, Vo= Vin.(R2/(R1+R2))

Assuming, R1= 10KΩ
put all the values in the formula ∴ 6= 12.(R2/(10K+R2))
We get, R2= 10KΩ

Now design the circuit with these components!!

Q. Can we apply voltage divider rule in parallel circuits?

Ans.
No you cannot apply voltage divider rule in a parallel circuit as it is only applicable to resistors in series. Only the reason that VDR is the modification of Ohm’s law.

Q. Do voltage divider rule only applicable to resistors?

Ans.
No, It can be applied to any passive element like capacitor and inductor. The only thing you have to assume is their impedance (Z).
Instead of the resistor in voltage divider rule, you need to use impedance along with the modified formula of impedance equations.
Zr for a resistor, Zc for a capacitor, Zl for an inductor.

Application of voltage divider rule and circuit :

1) It is used as a biasing circuit in the BJT amplifier.

2) Feedback Circuit in operational amplifier uses the voltage divider rule for driving the input and control the voltage gain.

3) It is the important circuit in comparator that is used for comparing different voltages whether the particular voltage is greater or smaller than the reference voltage.

4) The Logic Level Shifting use the voltage divider formula.

Something important to note:

• When the resistor R1 and R2 are the same, means, it is of the same value then the output voltage is exactly the half (50%) of the original input.
• Also, this circuit implies that it is useful where we don’t have a lower voltage source.
• It can be used as a substitute for the transformer ( only and only if the load is having large resistive impedance, we must use high wattage resistors say 3W/5W, it is very less practically used as it possesses the risk of electric shock)
• You noticed electrical line tester (live wire tester), it is nothing but voltage divider with resistor R1 and resistor R2 which is replaced with a high impedance low current consuming indicator light.

What is a Precision resistor?

A precision resistor is a normal resistor with near accurate Ohmic values. Technically they have very low tolerance value as compared to the normal resistors.
The lower the value of tolerance of the resistor shows the lower deviation from resistor value and higher the value of tolerance the higher the deviation from the actual standard value.
The Precision resistor is also called a film resistor or foil resistor.

The tolerance value is indicated in percentage (%).

You can say that if the tolerance value of the resistor is below 1% it can be classified under precision resistor, they have the tolerance in the range of 0.005%, 0.025%, 0.1%, 0.01%, etc

There are some other factors that are also considered while considering the precision in the resistance that will be discussed below in detail.
The resistance with the tolerance value 10%, 20%, 5% does not fall under the Precision resistor.

Ultra precision
±0.005%

Precision
±0.01%
±0.02%
±0.025%
±0.05%
±0.1%
±0.25%
±0.5%
±1%

General
±3%
±5%
±10%
±20%

Observe the difference among various tolerance values of the resistor and resultant value of resistor:

10k resistor 10% tolerance = 9000 to 11000 Ω
10k resistor 5% tolerance = 9500 to 10500 Ω
10k resistor 1% tolerance = 9900 to 10100 Ω
10k resistor 0.005% tolerance = 9999.5 to 10000.5 Ω

From the above observation, we can say that the nominal value of the resistor is between this two range and tolerance value play a great role if accuracy matters in your circuit.

Important factors of precision resistors:

• Technology involved: Wire-wound, Metal Film, Metal Foil, Bare Metal, Thin Film. All technology gives different results in resistor performance.

• Temperature coefficient ( ppm/°C ): It is the amount the Resistor value changes for every 1°C change in temperature.
  110 ppm/°C means the Resistance increases 110 Ohms for every 1M Ohm resistance for each degree rise in temperature. Or say ratio wise for other values, 11 ohms for every 100k or 1.1 ohm every 10k.
• Operating temperature: It indicates the operating temperature range of the resistor in which it remains stable, also can work without being damaged.
• Power rating: It indicates the power handling capacity of a resistor without being damaged.

Application of Precision resistor:

• Electronic weighing machine/ scales: Electronic weighing machine is two way the object and this purpose should be must be fulfilled with the accuracy, Precision resistor provide that accuracy in the circuit of the weighing machine.
• Audio application/ low noise amplifier: Audio device is one of the widely used devices that requires precise very low noise resistors and other components. Highly stable and linear response of Precision resistor Ideal for audio application.
• Commercial aviation industry: Highly accurate value of onboard instruments in the airplane is necessary as it operates and handles the critical conditions of such a Mammoth machine.
• Measuring instruments and meters: Digital multi-meters, LC meters, audio meters, altimeters, and all sort of measuring instruments install Precision resistors who has to give the measured value of a particular physical or electrical condition.

Precision Resistor color code: 5 band resistor color code and 6 band resistor color code

5 band and 6 band resistor color Code is generally used to indicate the color code of Precision resistors, the following table showing 5/ 6 band resistor color code:

Insertion loss and return loss are widely used terms in the field of microwave technologies. Insertion loss and return loss plays an important role in designing and development of high-frequency devices such as filters, power dividers, amplifier, etc.

These are quite similar concepts, it is an advanced form of the basic electronics we have learned in network theorems.

What is an insertion loss?

• Technically, when some system or circuit is inserted between a source and a load, some of the signal power from the source is dissipated through the circuit components due to their resistive nature that results in losses.Therefore, not all the transmitted signal power is transferred to the load when the load is connected to the source. The losses thus occurred is called Insertion Loss.
• It is a very important factor while designing and implementing microwave circuits. It is generally expressed in (dB) decibels.

If the power transmitted to the load is PT and the incident power received by the load is PR, then the insertion loss is given by:

What is a return loss?

• Practical circuit realization always suffers a certain level of mismatch between the impedance of the signal source and a load of a system (this load can be a transmission, line antenna, system filters or any device system).Some fraction of signal power inserted is reflected back due to mismatch between two systems, this fraction of power loss is called return loss.

Less power reflection is desirable thus high return loss (RL) is considered good according to the formula:

where RL is the return-loss in dB, Pi is the incident power to the system and Pr is the reflected power from the system.

Figure showing insertion loss offered by a bandpass filter, the required signal at another end will have some power loss:

What causes insertion loss?

Insertion loss causes due to two factors namely ohmic loss, dielectric leakage and the return loss is caused due to mismatched systems.

1. The first-factor ohmic loss is an unavoidable loss as it is a property of conductor used for connecting the components and the resistor used. Thus, to reduce ohmic losses the components are placed very closely integrated into a small confined area. VLSI and ULSI technology are used for making an integrated circuit that offers high efficiencies.
2. In the case of a capacitor, there is some leakage current through it can be reduced but cannot be omitted ideally. This is because of the dielectric in it, thus resulting in power loss.

Miss-matched in the system results in insertion loss and return loss. Ideally reflected power must be equal to zero but, in a practical sense, it has some value that can be up to 10 dB or more even after minimizing these losses.

• As the frequency increases insertion loss and return loss are more relevant in the systems due to the characteristics of microwave frequencies. The voltage standing wave ratio (VSWR) and reflection coefficient (Γ) are an important factor involved in return loss.
• Its basic version we have already learned in the Network theorems. The Maximum Power Transfer Theorem is significantly applicable in microwave frequencies, as the signal power one of the most considered and important factors in RF circuits while designing and implementing filters, amplifiers & power dividers.
• The MPT states that the maximum power is transferred from one circuit to another circuit (or one system to another system) when the impedance of the source is equal to the impedance of the Load.

For maximum power transfer,  Xs = Xl

This can be seen as,
When the source impedance is matched with load impedance then ideally return loss must be equal to zero. But practically, it has some value that can be up to 10 dB or more even if the system is matched.

Importance:

• Suppose that you have to transmit a signal through an RF remote control device operating on a small battery. The battery capacity of the remote control is generally very less as remote control must be portable and lite in weight, also long operating hours are expected.
• We need to increase the efficiency of the transmitter used in remote control ultimately do we need to reduce the return loss and insertion loss in the system used in the circuit.Also, the power generated by the transmitter must be efficiently transmitted by the antenna and therefore requires proper impedance matching of output ports of source and the antenna.
  It has its applications in the RF sector like Radars and satellite phones.

Relation with the scattering parameter:

Below image showing insertion loss and return loss for a 90MHz highpass filter matched at 50 Ohms.:

Insertion loss and return loss are linked with the scattering perimeter when the source and the load of the system is matched to the same reference impedance (say 50 Ohms).

S parameters are is the modern way of analyzing two-port networks. It is very helpful in in in optimizing the circuit to its best. It is capable of determining even smaller return loss and insertion loss in the form of s-parameters namely S11, S22, S12, S21:

S12 = transmission coefficient (power gain in dB of the system in a forward direction)

S21 = transmission coefficient (power gain in dB of the system in reverse direction)

S11 = reflection coefficient (related to return loss in dB at port 1)

S22 = reflection coefficient (related to return loss in dB at port 2)

For perfectly matched and ideal n/w:
→ S11 = S22 = 0
-→ S12 = minimum
–→ S21 = depends on the nature of the circuit (≥0)

Load resistor is an output testing device or component which is used as ideal output while designing or testing the electrical circuit.

To figure out what is a load resistor  in detail you should know about the term load, where it came from? what is its practical use? Various other forms of it in detail below.

What is a load?

The load is any device that can dissipate a considerable amount of power from the source to give the required output.
So this load can be resistive, capacitive, inductive load or combination of any two.

And the power consumed by them can be in the range of a fraction of Watts to several kiloWatts (uW to kW). The term load is broad in nature so we will try to cover that too in further discussion.

The name load is because it is seen as an added load to the circuit, moreover its characteristic is Load impedance.

Characteristics of the load:
a) It can be passive or active in nature.
b) It can be linear or nonlinear in nature.

There are three basic types of load impedance (Z):

i) Resistive load [Xr]
iii) Capacitive load [Xc]
iii) Inductive load [Xl]

What is a load resistor? -Resistive load:

The load in the circuit which is resistive in nature is called a resistive load or load resistor. The property of a material or a device to resist the flow of electrons through it is called resistivity.

The resistive loads exhibit the property of pure resistivity (there is no reactance or admittance which are the property of capacitor and inductor, XR ≠ 0, XC = 0 and XL = 0 which implies Z = XR )

Load resistor symbol:

Load resistor formula:

There is no such particular formula, but if you want to find it then refer to the output resistance of amplifier (in the case of the amplifier only)

• Furthermore, the load resistor is temporary and a mocked output device for designing and testing purposes only.
  You will find this ‘TERM‘ in educational curriculum and tutorials but never in real life practical circuits.
• In other words, it is simply a resistor that’s been used as a load in various circuits especially which are under test or for experimental purposes.

Additionally, in practical circuits, there is nothing like a load resistor. This is because output devices with a specific name is used everywhere instead of it.

Example of load resistor:

• This can be seen as a speaker is used as an output device in an amplifier circuit in the place of load resistor (RL).
• Besides this LED/ lamp/ light bulbs is used as an indicator in the power converter circuits as an output device instead of (RL).
• Note that the load resistor value can be anything that can handle the output power from the source circuit.

What is a load resistor in circuit?

Below are those things that can be load resistance:

1) Simple resistor
2) Audio speakers
3) LED lights
4) All types of the light indicator
5) Resistive sensors
6) Buzzers
7) The output stage of the radio frequency amplifier or audio frequency amplifier.
8) Antennas
9) High wattage resistor

It also recognized as a discharge load resistor, this type of device has its application in discharging the stored energy in the output capacitor to avoid electric shock or damage of output devices.

USB mini discharge load resistor is commercially available for sale online. Its objective is to discharge USB source circuits so as to avoid accidental electric shock.

Variable Load resistor:

As the name suggests, variable + load + resistor. It is the load that is having variable resistance that can be controlled either manually or by some other means. This image showing a variable load resistor available for the experimental purpose in labs. It comes with various wattage ratings from 5 Watts to 100 Watts and so on. It is also called as a potentiometer.

Generally, a variable load resistor is used to test the effect of Load resistance on the power consumed by the circuit and several other parameters.

ii) Capacitive load:

The load in the circuit which is capacitive in nature can be termed as capacitive load.
The capacitive load can be the combination of capacitor and inductor in which capacitance should be greater than that of inductance (XC > XL). Or the circuit must contain the capacitor only.

iii) Inductive load:

The load connected in the circuit which is inductive can be termed as inductive load.
The inductive load can be the combination of an inductor and capacitor in which inductance should be greater than that of the capacitor (XL > XC). Or the circuit must be purely made of inductors.

FAQ:

What if we don’t use load resistance?

In such case we can not understand the nature of circuit when used load connected and thus circuit analysis is affected.

What if we use a very small load in the power/electrical circuit?

The circuit will deliver a large current and may cause a short circuit which in results can destroy the driver circuit.

Unlike other filters, a high pass filter has its unique importance. The basic mode of communication is voice calling. Of all forms of communication, voice calling is still the most preferred form of communication.

Also, it has challenges while communicating a long distance over the telephone, the only information/data required is voice signal and therefore, it is necessary to maintain the quality of transmitted and received voice signal.

However, a lot of noise interference of low frequency is added to the communication channel. To avoid this highpass filter is used (HPF because the human voice is having a higher frequency than that Of noise).

What is the high pass filter?

A high pass filter is a circuit that allows the higher frequency above cutoff frequency and attenuates all the frequency below the cutoff frequency (ƒc).

As we have already studied low pass filter which blocks low frequency passing through it and only allows higher frequencies to the output, but on the other hand, high pass filter is opposite to that of low pass filter.

The high pass filter circuit is essential in the day-to-day application in the field of audio applications such as voice recording voice filtering music tone control and so on.
It is widely used for eliminating ‘hiss’ noise, and noise of wind while recording through the microphone in an open environment. We have discussed this in the application section below in detail.

Ideal Vs Practical High Pass Filter

The figure is showing the frequency versus attenuation response curve of the high pass filter. Ideal having very flat response i.e., infinite loss/ attenuation at stop-band and Zero attenuation at passband frequency, but practically due to ohmic losses and lossy components, practical HPF has finite attenuation at stopband and few dB of loss at passband.

The frequency response of High Pass filter:

A) -3d dB cutoff frequency is nothing but half of the power at output than at input.
Alternatively, (1/√2=) 70.7{42041a7992ac3be9e9e29c856254fb498d8c7935d7cf8512da6802e8688e734a} of Vin

B) If you have values given in voltage, can be to convert them in dB using this formula:
dB = -20log (Vout/Vin)

Types of high pass filter:

This filter is classified on the basis of the component used to implement the circuit as LC or RC.

A) HPF using R & C:

There are two schematics generally used in the filter. The filter that uses a resistor in the circuit is used in combination with an external power supply called active filter, otherwise passive filter.

The Other method is to design filter using RC and then amplify the signal, that filter without any external power source is called a passive filter.

The figure showing the schematic of HPF using RC along with the formula:

The capacitor is in series with the input, and the resistor is parallel to the input. Also, the output is taken across the resistor, as shown in the figure. The role of a capacitor here is to block the DC signals (lower frequency signals) which is determined using the formula.

The product of capacitance C and resistor R is time constant (Tau)

ƒc = 1/(2πRC)

where, fc is in hertz,
R in ohm,
C in farad,
therefore (τ)is in sec.

B) High pass filter using L and C:

You might have observed that the formula for deriving the component values in the filter is the same for all the types of filters i.e. HPF, LPF, and BPF.
Then, How are you getting different responses for different types of filter?
The answer is the position of capacitor C in the schematic.

• When the capacitor is kept in series with the source, then it is a high pass filter.
• On the contrary, if you placed the capacitor in parallel with the source, then it is a low pass filter.

Figure showing LC high pass filter schematic and formula:

Why is LC filter better than RC or RL filter?

The answer is simple: it offers theoretically zero power loss due to two non-resistive elements and makes no ohmic losses.
Therefore, it is preferable in the circuit at the receiver end, where we have to pick very small RF signals. It is quite complex to design inductor but it worths it.

Higher-order filters:

A higher-order filter can be achieved by cascading two or more stages of the filter. These stages of the filter are either schematic of RC or LC. The order of the filter is increased so that we get a very sharp response curve that is near to the Ideal filter. The first-order filter gives a slope of 20 dB/decade.
If we add 2nd stage in series with the first stage then 40 dB/ decade is achieved.

Practical example to design High pass filter:

Design a high pass filter fc=1.2 kHz using RC?

Given- fc=1.2kHz

R=100Ω (assumed)

find C using formula:  ƒc = 1/(2πRC). And it came out to be 1.32uf

Design a high pass filter having cutoff frequency fc=3 MHz using RC components?

Given- fc=3MHz

R=100Ω (assumed)

find C using formula:  ƒc = 1/(2πRC). And it came out to be 0.53nf

Design a high pass filter having cutoff frequency fc=90 MHz using LC components?

Given- fc=90MHz

C=25pf (assumed)

find L using formula:

ƒc = 1/(2π√LC).

And it came out to be ~62nH

What is high pass filter used for? Its applications.

1) While recording audio outdoor using a mic, causes the sound of wind also gets recorded as noise. The frequency of the human voice is slightly higher than that of the noise of the wind.
The sound of the wind is of lower frequencies which are unnecessary, therefore, high pass filter is used to lower the noise.

2) In pre-amplifier to avoid amplification of noise

3) To reduce ‘Hiss’ sound in the audio circuit (caused due to power lines nearby).

4) For Waveshaping in different applications in analog and digital electronics.

5) It is used as differentiator circuit(converts square wave/ step response to spike/impulse)

6) As an audio equalizer, then this filter is called treble boost filters.

Bonus Tips/Overview:

In short, High filter makes it difficult for a low frequency to pass through it and eases high frequency to pass through it.

The trick to identifying whether the filter is a highpass filter or low pass filter?

a) if the position of the capacitor is lower that is a low pass filter (parallel to the input)
b) if the position of the capacitor is upper then it is high pass filter (in series with input)

What is a Band pass filter?

Band pass filter circuit is an electronic circuit that is used to pass the frequencies in a particular frequency range so that only a certain frequency is obtained for further processing in the application circuit.”

Alternatively, it can be said that “Band pass filter attenuates all the signal outside the particular frequency range allowing only certain signals to receive.”

The frequency which is allowed, that range of that acceptable frequency is known as pass band. The difference of higher allowed frequency to the lower allowed frequency is called bandwidth of the filter.

This circuit is useful for removing unwanted noise signals by blocking them. The Band pass filter has a lot of applications ranging from audio circuits to the radio frequencies circuits.

Generally, RF bandpass filters are used in transmitters and receivers so that we transmit the data signals to the required destination without interfering with other signals. Because interfering with another signal may cause confusion and cross-talks among the transmitter and receiver.

Importance:

• Filtering is one of the most used methods to get rid of noise in the circuit besides the modulation technique and different other methods.
• These circuits are the weapon for electronic circuit designer who uses this to deal with noise in the circuits special RF receivers in communication devices.
• You can find the simple use of this type of filter in the audio amplifier for driving loudspeakers.
• There you can control the tone of the output music/sound, controlling tone is nothing but the controlling of a pass frequency to the output loudspeaker.
  Later on, we will discuss in brief the area of application of the Band pass filter below in the application section

Working of Band Pass Filter :

We have already discussed the working of a low pass filter. The similar is the working of a band-pass filter except for a few extra circuits.

It is the combination of a low pass filter and high pass filter so the formula for cutoff frequency we already discussed {here}

The basic idea of implementing bandpass filter is as shown in the figure:

• The ideal bandpass filter and the practical bandpass filter frequency response is as shown in figure. As you see that the Band pass filter has the infinite attenuation for the blocked frequencies and zero attenuation for passband frequencies.
• But in practical this is not possible, the practical bandpass filter offers of zero to one dB attenuation for passive filters which also depends on the type of filter, whether it is RC filter or LC filter? and /or it is passive filter or active filter, which we will discuss below.

Types of Band Pass filter:

Ultrabasic classification is Analog filter and Digital filter. We are discussing here is analog(check below at last for digital filter). Also, basic types of filters are active filters and passive filters.

Active filters are those which require some sort of external power supply(and active components like transistors) to give the required outcome.

On the contrary,
Passive filter does not require any type of active components to do its work and thus preferable in Low-cost circuits.

Now the real bandpass filter is classified into two types based on its bandwidth as follows:

1) Wideband filter.
2) Narrow-band filter /tuned filter.

WideBand pass filter BPF :

The wide-band filter is implemented using One circuit of low pass filter and high pass filter.

• The low pass filter blocks the lower frequencies which are not required and passes all the other frequencies, at the same time the high pass filter blocks the higher frequency than required and passes the frequencies lower than that. Take a look at the following diagram to understand it in a better way.

(BPF using resistor and capacitor,)

• The wide band filter has quite a lower Q factor. The BPF can be implemented using RC or LC, ie. using a resistor-capacitor for inductor-capacitor.
• The best is to use the Inductor capacitor filter as it has a low power loss. We have discussed the RC filter in low pass filter so we will discuss the LC here in the example below.

Narrow band filter:

• It is also called a tuned filter. As its name suggests that it will pass only a narrow range of frequency through it. The construction of a narrow band filter is quite different.
• The resonance circuit is used to implement a narrow band filter. This is the most favorite filter in all classes of the filter this is because it uses only two components the one is inductor and another is a capacitor in a very simple configuration as shown in the figure. This configuration is called a tank circuit.

• In this circuit the inductor and capacitor value is chosen such a way that it resonates at a particular frequency, rather say the transfer of charges (current/ energy) from the inductor to capacitor and capacitor to inductor depending on their capacities to hold charges. (This is practically used in various application but lesser taught in the curriculum)

Important definitions:

1) SNR: Signal to noise ratio, it is very important down while designing filters and RF circuits especially transmitters and receivers, also equally important in audio circuits. SNR is the ratio of signal power to noise power.

• Further for ease, the factor used to determine the quality of signal received at the application end is signal to noise ratio.
• The power of the signal must be greater then that of the noise, real noise is the frequencies of unrequired signals which may be natural or artificial for propose full or unintentional.
• Generally, the value of 20 dB for higher than that is considered a good network signal. Similarly, 3dB is a minimum acceptable Value below that value it is very difficult Orra impossible to detect the required signal with accuracy.

2) Q factor: It is lease also called a damping factor it is a dimension list that gives information about the bandwidth with respect to its central frequency. It is used in the circuit having LC in parallel( tank circuit).

Band pass filter example (practical):

Design a bandpass filter having frequency range 80Mhz to 120Mhz?

Given- fc1 and fc2    (where, fc1 =fl =lower cutoff frequency & fc2 = fh = higher cutoff frequency)

The above circuit is designed using the inductor and capacitor as we have already discussed the upper hand of the LC filter over the RC filter, so we will design the bandpass filter using the inductor.

step1: for LPF
L2 = 10 nH  (assumed) & C2 = 0.395 nF (using formula).

step2: for HPf
L1 = 10 nF & C1 = 0.395 nF

(for both LPF and HPF the values came out to be same because for LC filters formula for finding L&C is same only the position of inductor and capacitor interchanges “look fig.”)

Design a narrow bandpass filter having Centre frequency Fc=100Mhz?

Use narrow band pass filter circuit,

Fc=1/2π.sqrt(LC)

Here, the only frequency value is given then how can we calculate the value of L & C ?

-You have to assume the value of any one component either it is an inductor ‘L’ or a capacitor ‘C’.

-Let’s assume, C=1.58 nF (assume the standard value which is available to you)

-then using formula, find L, it came out to be 1.56 nH.

Hence, the circuit is completed. (see image for schematic)

4th order bandpass filter and 5th order Bandpass filter:

The effect of the orders of filters on the response is displayed in the image below. Just observe the attenuation of the pass frequency and stop frequencies.

• The attenuation roll-off of each is different in different orders of filters.
• The picture is showing 1st order bandpass filter, 2nd order bandpass filter, 4th order bandpass filter, 5th order bandpass filter.
• 1st order filter has -20dB/decade gain roll-off than that of -40dB/ decade for 2nd order filter and so on.
• The order of the filter is achieved by cascading the number of stages of the same filter and sometimes using modern topologies.

Application of Band Pass Filter:

1) Radio transmitter and receiver widely use BPF.

2) Optimization of signal to noise ratio so as to reduce the probability of error in the receiver.

3) In almost every Audio Tone control circuit to increase or decrease the tone in the music.

4) It is an important circuit in demodulators in the receiver circuit.

5) Band selection in FM radio receivers, also in mobile communication systems.

6) In pre-emphasis and de-emphasis circuits to increase S/N.

7) In RADAR to transmit signals in a different spectrum.