Definition of Band Stop Filter (BSF) or Notch Filter

Band Stop Filter is a filter or frequency filter that rejects and block frequencies that are between two cut-off points, while all frequencies that are below a certain frequency (below the cut-off point) and all frequencies above a certain frequency (above the cut-off point) will be Dilewatkannya. In other words, Band Stop Filter will skip all frequencies which are outside both sides of the cut-off point range

Band Stop Filter or also often called with Notch Filter is basically a combination of Low Pass Filter and High Pass Filter which is connected in parallel. This connection differs from the Band Pass Filter which connects Low Pass Filter and High Pass Filter in series. Another mention for this Band Stop Filter is the Band-Elimination Filter or the Band-Reject Filter.

Please note that the Band's characteristic Stop Filter (BSF) is against the characteristics of the Band Pass Filter (BPF). When the input signal is given, low frequencies are passed through the Low Pass Filter on the BSF circuit. Similarly, high frequencies will be passed through the High Pass Filter on the BSF series as shown in the block diagram and the characteristics form of the Band Stop Filter below.

From the characteristic image above it looks that fL is the cut-off frequency at Low Pass Filter and fH is the cut-off frequency at High Pass Filter. While the frequency of the middle (Frequency center) or fC = √ (fLx fH).

Circuit Band Stop Filter

As mentioned earlier, Band Stop Filter or Reject Filter bands basically consists of two filters namely Low Pass Filter and High Pass Filter which are then connected in parallel. The basic set example of a Band Stop Filter can be seen from the image below:

Formula Band Stop Filter

The formula or equation used in the Band Stop Filter is essentially the same as the formula used in the Low Pass Filter and High Pass Filter. Below is the formula used for frequency filtering by using the Band Stop Filter.

f = 1/2πRC


f = Frequency in Hz units
π = 3.14
R = Resistor value in OHM (Ω) unit
C = capacitor value in Farad unit (F)

Example of Band Stop Filter calculation

A series of Band Stop filters are designed from RC (Resistor – Capacitor) components to skip frequencies below 300Hz and frequencies above 1kHz. The capacitor used on the circuit is 0.1 Μf. What is the Resistor used in the Band Stop Filter?

The calculations are divided into two phases of calculation namely the stage calculation in the LOW PASS FILTER section and the stage in the HIGH PASS FILTER section.

Calculation phase of LOW PASS FILTER

Finding the value of The Rlwhich is necessary to provide the frequency of cut off File 300Hz by using a capacitor of 0.1 Μf is calculated through the calculation below:

FL = 1/2 πRLC
300Hz = 1/2 x 3.14 x RL x (0.1 x 10-6)
RL = 1/2 x 3.14 x 300 x (0.1 x 10-6)
RL = 5,308 Ω or approx. 5, 3kΩ

So the Resistor value required to produce the cut-off frequency of Flis 5,308 Ω or about 5, 3kΩ.
Calculation phase on the HIGH PASS FILTER

Looking for Resistor value RHyang necessary to give The frequency of cut off fHyaitu 1kHz with a capacitor value of 0.1 Μf is calculated through the calculation below:

fH = 1/2 πRHC
1000Hz = 1/2 x 3.14 x RH x (0.1 x 10-6)
RH = 1/2 x 3.14 x 1000 x (0.1 x 10-6)
RH = 1,592 Ω or approx. 1, 6kΩ

So the Resistor value required to produce frequency cut off This 1,592 Ω or about 1, 6kΩ.

Calculating frequency Center (fC)

We can also calculate frequency Center or fC with the formula below:

fC = √ (fL x fH)
fC = √ (300 x 1000)
fC = √ 300,000
fC = 547, 72Hz

So frequency Center or fC of the BSF range is 547, 72Hz.

Band Stop Filter application in various fields

The following is the utilization of the Band Stop Filter range in various fields.

  1. In phone technology, this Filter called Notch Filter is used as a noise reducer in the phone line and DSL Internet service. This will help eliminate distractions on the channel that will reduce DSL performance.
  2. The BSF range is widely used in electric guitar amplifiers. In fact, this electric guitar produces a ' hum ' at a frequency of 60 Hz. This Filter is used to reduce buzz in strengthening the signal generated by the guitar amplifier and make the equipment better. BSF is also used in some acoustic applications such as mandolin and instruments that use amplifiers.
  3. In electronic signal, communication is distorted because some noise (Harmonisa) that makes the original signal is interrupted by another signal thus causing an error in the output result. Thus, this filter is used to remove the unwanted distortion.
  4. This BSF range is used to reduce static on the radio, which is commonly used in our daily lives.
  5. The BSF range It is also used in optical communication technology, at the optical fiber end there may be some disruptive light frequencies that make distortion on beam light. This distortion can be eliminated by using the Band Stop Filter. The best example is in Raman spectroscopy.
  6. In image processing and signal, this filter is very useful for resisting noise.
  7. BSF is also used in high-quality audio applications such as PA systems (Public Address systems).
  8. The Filter, also known as the Reject Filter Band, is often used in medical field applications, such as biomedical instruments to remove line noise in EGC.