Category: 4. Filters

The state variable filter is a type of multiple-feedback filter circuit that can produce all three filter responses, Low Pass, High Pass and Band Pass simultaneously from the same single active filter design. State variable filters use three (or more) operational amplifier circuits (the active element) cascaded together to produce the individual filter outputs but if required an additional summing amplifier can…

In the previous filter tutorials we looked at simple first-order type low and high pass filters that contain only one single resistor and a single reactive component (a capacitor) within their RC filter circuit design. The Butterworth filter is an analogue filter design which produces the best output response with no ripple in the pass…

Second Order (or two-pole) Filters consist of two RC filter sections connected together to provide a -40dB/decade roll-off rate. Second Order Filters which are also referred to as VCVS filters, because the op-amp is used as a Voltage Controlled Voltage Source amplifier, are another important type of active filter design because along with the active first…

The principal characteristic of a Band Pass Filter or any filter for that matter, is its ability to pass frequencies relatively unattenuated over a specified band or spread of frequencies called the “Pass Band”. For a low pass filter this pass band starts from 0Hz or DC and continues up to the specified cut-off frequency point at…

An Active High Pass Filter can be created by combining a passive RC filter network with an operational amplifier to produce a high pass filter with amplification. The basic operation of an Active High Pass Filter (HPF) is the same as for its equivalent RC passive high pass filter circuit, except this time the circuit has an…

By combining a basic RC Low Pass Filter circuit with an operational amplifier we can create an Active Low Pass Filter circuit complete with amplification. Active filters such as an active low pass filter, are filter circuits that use an operational amplifier (op-amp) as the their main amplifying device along with some resistors and capacitors…

Passive Band Pass Filters can be made by connecting together a low pass filter with a high pass filter. The Passive Band Pass Filter can be used to isolate or filter out certain frequencies that lie within a particular band or range of frequencies. The cut-off frequency or ƒc point in a simple RC passive filter can…

A High Pass Filter is the exact opposite to the low pass filter circuit as the two components have been interchanged with the filters output signal now being taken from across the resistor. Where as the low pass filter only allowed signals to pass below its cut-off frequency point, ƒc, the passive high pass filter circuit…

A Low Pass Filter is a circuit that can be designed to modify, reshape or reject all unwanted high frequencies of an electrical signal and accept or pass only those signals wanted by the circuits designer. Passive RC filters “filter-out” unwanted signals as they separate and allow to pass only those sinusoidal input signals based…

Capacitive Reactance is the complex impedance of a capacitor who’s value changes with respect to the applied frequency. Capacitive Reactance is the complex impedance value of a capacitor which limits the flow of electric current through it. Capacitive reactance can be thought of as a variable resistance inside a capacitor being controlled by the applied frequency.…