Band Pass Filter Calculator

Enter Desired Center Frequency (Hz): Enter Desired Q (and Gain V/V): Select Resistor Sequence: E96 E24 Select Capacitor Sequence: E24 E12 E6 Select Resistor Scale (Ohms): 1 10 100 1000 10000 100000 1000000     C1, C2 (pF) Ro (Ohms) Rq2 (Ohms) Rq1 (Ohms)

The Q and gain are linked together - adjusting one affects the other. RQ1 and RQ2 resistors are adjusted proportionally. To increase the gain and Q, multiply Ro by a factor to get RQ1, and divide Ro by the same factor to get RQ2. The responses below were obtained for various values of Q and gain:

Notes:

• Practical limits are a Q of about 50 on the high end, and 1 on the low end.
• The open loop gain of the op amp selected must be at least 40 dB greater than the gain of the op amp at the resonant frequency.
• The input impedance of the op amp becomes important as RQ1 increases in value, for large values of Q you may need an FET input type op amp. You can combat this by scaling the R's and C's, but remember you need to use an NPO type capacitor for stability.