# 300Mhz-1Ghz band pass filter design

Discussion in 'Homework Help' started by jndugga, Mar 11, 2011.

1. ### jndugga Thread Starter New Member

Feb 23, 2011
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Hello evry one there. i have been trying to design a bandpass filter for the 300Mhz-1Ghz frequency range. first i designed one which passes low frequencies like from 65mHz to about 560kHz...thereafter i changed the values of the resistors and capacitors to get my pass band to be close to 300Mhz to 1GHz, but it aint working at all.im doing all this in multisim. since the two cut off frequencies are known, the equations below helped get the resistor and capacitor value. i set one and found the other

f(lower )= 1/(2*pi*R4*C1)

f(lower )=300MHz. i set my C1=1pF and it yielded, R4=530 ohms

and
f(upper)= 1/(2*pi*R2*C2)

f(upper )=1GHz. i set my C2=1pF and it yielded, R2=160 ohms....from this it seems the frequencies i want in the pass band are actually 2wards the end of the pass band and strictly the 1GHz is outside..how can i have them well within the pass band and also with a gain >=0 attached is my circuit

also if u look at the pass band gain it's at -54dB, how can i increase it

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2. ### blueroomelectronics AAC Fanatic!

Jul 22, 2007
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What's the upper frequency limit of that OpAmp?

3. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
You need a different op amp. That one is electrometer grade because of the input impedance, but is unity gain characterized only up to 1 MHz.

4. ### Kermit2 AAC Fanatic!

Feb 5, 2010
4,158
1,125

Check out the first three returns (at least)

http://www.national.com/pf/LM/LMH6702.html#Overview
http://www.eecg.toronto.edu/~sorinv/papers/georgeng_SiRF06.pdf

1 GHz BW capable op amps are a very new phenom just announced in 2009 and only recently widely available. You can expect a long search to find anyone selling them in 1 each quanity

5. ### jndugga Thread Starter New Member

Feb 23, 2011
8
0
hello every one there, i noticed i was using the wrong opamp, it's upper frequency limit was way too low. Now i am using an LMH6702. its data sheet says it has a 1.7GHz bandwidth. i want to increase the gain to some value close to 0dB,either slightly above o below. How can i achieve this? please see the attached circuit

I really appreciate all your help.

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