Pasif Bant Geçiren Filtre / Passive Band Pass Filter

Passive Band Passing Filter can be used to isolate or filter specific frequencies within a specific band or frequency range. The cutting frequency or εc point in a simple RC passive filter can be controlled correctly using only a single resistance in series with a non-polarized capacitor. Depending on which way they were connected, we found that a low-pass or high-pass filter was obtained.

A simple use for such passive filters is in circuits, such as in audio amplifier applications, speaker crossover filters or pre-amplifier tone controls. Sometimes it is necessary to pass a certain frequency range that does not start with only 0Hz, (DC) or end at a higher high frequency point, but is in a narrow or wide specific range or frequency range.

Tape Passive Tape Passing Filter Circuit

Tape Passive Tape Passing Filter Circuit

Unlike the low pass filter, which transmits only signals in the low frequency range, or the high pass filter that transmits signals in a higher frequency range, Filters that pass a band pass signals within a specific "band" or "propagation" of frequencies without disrupting the input signal or bringing extra noise. This frequency band can be of any width and is often known as filter bandwidth.

Bandwidth is usually defined as the frequency range between two specified frequency breakpoints (εc), which are 3dB below the maximum Center or resonance peak, while weakening others other than these two points.

Then for commonly spread frequencies, we can define the term "bandwidth" as the difference between the points of lower cutting frequency (εcLOWER) and higher cutting frequency (εcHİGHER). In other words, BW = εH – εL, for a transition tape filter to function properly, the cutting frequency of the low transition filter must be higher than the cutting frequency of the high transition filter.

The "Ideal" passive band passing filter can also be used to isolate or filter certain frequencies in a specific frequency band, such as noise cancellation. Tape-passing filters are often known as second-order filters (bipolar), since circuit designs have "two" reactive components, capacitors.

Frequency Response of The Filter That Passed Passive Band from The Second Degree

Frequency Response of The Filter That Passed Passive Band from The Second Degree

The Bode chart or Frequency response curve above shows the properties of the tape-passing filter. Where the signal is weakened at low frequencies with increased output at the +20db/decade (6dB/octave) slope until the frequency reaches the "lower interrupt" point εL. The output voltage at this frequency is 1/√2 = 70.7% of the re-input signal value or -3db (20*log(VOUT/VIN)).

Output continues at maximum gain until it reaches the "top cutting" point, where output weakens any high frequency signal by -20dB/decade (6db/octave). The maximum output gain point is usually the geometric mean of the two-3dB value between the lower and upper breakpoints, and the value "Center frequency" or "Resonance peak" is called εr. This geometric mean value is calculated as εr 2 = ε(top) x ε(child).

Since there are "two" reactive components within the tape-passing filter circuit structure, a second order type with poles (2) is considered a filter. Then the phase angle will be the first-degree filters we've seen before, that is, twice the volumetric. The upper and lower cutting frequency points for a tape-passing filter can be found using the same formula, for example, for both low and high passing filters.

Completed Tape Pass Filter Circuit

Completed Tape Pass Filter Circuit

Tape Passing Filter Resonance Frequency

In case the output gain is at maximum or peak value, we can also calculate the "Resonance" or "Central frequency" (εr) point of the tape-passing filter. This peak value is not the arithmetic mean of the upper and lower-3dB breakpoints as you would expect, but is actually "geometric" or average. This geometric mean value is calculated as εr 2 = εc(top) x εc(child).

Center Frequency Equation

Center Frequency Equation

Where εr is resonance or Central frequency
εL is low -3db cutting frequency point
εH is the upper -3db cutting frequency
point, and in our simple example above, it was found that the cutting frequencies calculated using filter values were εL = 1,060 Hz and εH = 28,420 Hz.

Then a central resonance frequency is obtained by changing these values to the equation above: