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Bandpass Filter

Posted on 11:50 AM Under 0 comments

Bandpass filter ( BPF ) Between passes all frequencies lower (FL) and upper ( FH )-3-dB points while rejecting those outside the MH - ML range. Figure 1 shows the implemented BPF circuitry. It is made ​​up of three cascaded -element low-pass filter ( LPF ) and High-Pass Filter ( HPF ) using pi-filter configuration. The LPF is designed by having a cutoff frequency equal to the high cutoff frequency in the passband , and the HPF is designed to cutoff and Desired the low point in the passband .
             
Figure 1. BPF Circuitry

Shown in Figure 1, the RF signal is filtered through this BPF circuitry before being passed on to the next stage in order to limit the amplification of the noises and unwanted signals. The BPF has set its operating frequency and FL and F = 60 MHz H = 66MHz.
In order to tune the detector Desired accord ing to the operating frequency, the filter design of inductor-capacitor (LC) filters for radio frequency (RF) used in this paper is the normalized 1-MHz model. In this design approach, a model is built by calculating the component values ​​for 1 MHz. The component values ​​can be scaled for any frequency by Dividing the 1-MHz frequency value by the Desired frequency, ie is expressed in megahertz.
Low-pass filter equations:
L μH = K1/Frequency (in MHz)                                                            (1)
and
            C pF = K2/Frequency (in MHz)                                                            (2)

These equations (1) and (2) will also be used to Calculate the values ​​of the components to other filters, though the numbering of constants K will be different and their values.

Filter Design Constants for Low-pass filter

K1
K2
(Not Filtered)
7.94
6360
(Pi-filter)
15.88
3180

Using equations (1) and (2) for LPF with a cutoff frequency of 66MHz, 
               Pi-filter: 
                      L μH  = L1 = K1/Frequency = 15.88/66 = 0.241 μH 
                      CpF= C1 = C2 = K2/Frequency = 3180/66 = 48.2 pF 


           High-pass filter equations:  
                                     L μH = KL1/Frequency (in MHz)                                                            (3) 
                        and 
                                     C pF = KC1/Frequency (in ΜHz)                                                            (4)
    
                                 Filter Design Constants for High-pass filter

KL1
KL2
KC1
KC2
(Not Filtered)
3.97
------
3180
3180
(Pi-filter)
7.94
7.94
1590
------

Using equations (3) and (4) for HPF with a cutoff frequency of 60MHz, 
              Pi-filter:  
                     L μH   = L1 = L2 = KL1/Frequency = 7.94/60 = 0.132 μH 
                     CpF = C1 = KC1/Frequency = 1590/60 = 26.5 pF

That's it test your design by making a circuit. Tune it and test it again. Thanks! 

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Paul Ryan A. Dedumo is a blogger and an Electronics and Communication Engineering student at University of San Carlos. Learn and inspire as you follow him in his links, blog and other social media accounts.

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