Notch Filter Made With High and Low Pass Filter

Figure 1 

The circuit was designed with the combination of high pass filter and low pass filter to create a notch filter circuit.

• High Pass Filter – an electronic circuit that allows the passage of high frequencies while opposing any unwanted low frequency components
• Low Pass Filter – an electronic circuit that allows the passage of low frequencies while reducing the amplitude of frequencies higher than the frequency response limit of the system
• Band Pass Filter – an electronic circuit the allows the passage of certain frequencies within a predefined range while denying frequencies beyond that range
• Band Stop Filter – an electronic circuit that allows the passage of nearly all frequencies unchanged while reducing the amplitude of frequencies within the predetermined range to very low levels
• Notch Filter – a type of band stop filter that has high quality factor and limited band of frequencies

The filter circuits are responsible for performing signal processing functions, specifically intended to remove unwanted signal components. The wideband single JFET operational amplifier LF351 is used in this circuit with features such as high slew rate, latch up free operation, internal frequency compensation, high input impedance JFET input stage, output short circuit protection, low input bias and offset current, wide common mode and differential voltage range, low power consumption, low offset voltage temperature coefficient, and internally adjustable input offset voltage. Lastly, these are high speed JFET input single operational amplifiers integrating bipolar transistors in a monolithic IC and well matched high voltage JFET.

The gain of the circuit has a sum total of 20 from the mixture of high pass filter and low pass filter as the circuit can be separated down into these two filters. The single voltage provided or the rail voltage was 9 V DC. By modifying the controls of the circuit, it can function as a band pass filter or as a notch (band stop) filter.

When a filter operates as high pass filter, it may be utilized in digital image processing in spatial frequency domain where transformations are performed, in amplifiers where alternating current is coupled at the input and output, in loudspeaker where it functions as passive filter, in rumble filters where unwanted sounds are removed near to the lower end of the audible range, and as part of audio crossover to prevent any damage or interference to the speaker, by blocking the bass signals and directing high frequencies to a tweeter.

Low pass filter circuits are used in radio transmitters to prevent the causes of interference with other communications by blocking harmonic emissions, as integrator, as DSL splitters where POTS and DSL signals are separated on the sharing of wires, and for blocking high pitches when powering different types of loudspeakers and subwoofers.

The band pass filters may be used mostly in resistor-inductor-capacitor (RLC) circuit functioning as harmonic oscillator, in atmospheric science where meteorological data are gathered, and in neuroscience wherein it resembles the response properties a Gabor filters.

Notch filters were mainly used in public address (PA) system for live sound reproduction, in instrument amplifier to reduce the feedback for on instruments like bass instrument, mandolin, acoustic guitar, and others, and in power amplifiers where non-linearities are measured by preventing excess maximum input power.

Source:www.zen22142.zen.co.uk/Circuits/Audio/notch.htm