Filters (13)

Sallen and Key Filter

The Sallen and Key Filter design is a second-order active filter topology which we can use as the basic building blocks for implementing higher order filter circuits, such as low-pass (LPF), high-pass (HPF) and band-pass (BPF) filter circuits. As we have seen in this filters sect...

Decibels

Generally, decibels is a measure of loudness. When designing or working with amplifier and filter circuits, some of the numbers used in the calculations can be very large or very small. For example, if we cascade two amplifier stages together with power or voltage gains of say 20...

Band Stop Filter

By combining a basic RC low-pass filter with a RC high-pass filter we can form a simple band-pass filter that will pass a range or band of frequencies either side of two cut-off frequency points. But we can also combine these low and high pass filter sections to produce another k...

State Variable Filter

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 also be added to produce a fourth Notch filter output response as well. S...

Butterworth Filter Design

The Butterworth filter is an analogue filter design which produces the best output response with no ripple in the pass band or the stop band resulting in a maximally flat filter response but at the expense of a relatively wide transition band. In applications that use filters to...

Second Order Filters

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 order RC filters we looked at previously, higher or...

Active Band Pass Filter

For a low pass filter this pass band starts from 0Hz or DC and continues up to the specified cut-off frequency point at -3dB down from the maximum pass band gain. Equally, for a high pass filter the pass band starts from this -3dB cut-off frequency and continues up to infinity or...

Active High Pass Filter

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 operational amplifier or included within its design providing amplification and gain control. Like the previous acti...

Active Low Pass Filter

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 to provide a filter like performance at low frequencies. Basic first-order passive filter ...

Passive Band 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 be accurately controlled using just a single resistor in series wi...