# 8th order bandpass with LTC1562 and Total Q value

Hello,

I want to design 8th bandpass filter with LTC1562. I can calculate Q1..Q4 values from datasheet but I don't find total Q and bandwidth.

There is some quick design formulas for bandwidth=-3dB  & Q=10 on page 16 in datasheet but I need different Q ve BW values.

Please can you show me how I can calculate?

thanks

• hello again,

Are the following calculations correct approximately ?

if gain and Q  of four stages are same,   for example, if gain is 1 and Q is 4

total gain =1 (G1*G2*G3*G4)

get center Frq=100khz, stage1: BW= 100Khz / 4 = 25Khz ( fH=125Khz,fL=75Khz but amplitude decreases -3dB)

end of stage4 : -3dB*4=- 12dB so

( at fH=125Khz, at fL=75Khz but amplitude decreases -12dB) ,

for  new BW at -3dB

I found BW=25Khz at -3dB,

for new BW, can I say  25Khz/4=6-7Khz? (-12dB/-3dB=4, Assuming linear )

BW=93Khz--107Khz (-3dB)

• Hi Kutay,

Apologies for missing thing item. We will look into this, I'll contact the product owner and get back to you. Thank you!