2006-07-02 03:26:52 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Engineering
I use picofarad value capacitors for charge sensitive preamplifiers. Many sensors such as photomultiplier tubes, photodiodes, and various radiation detectors will output current pulses in proportion to the radiation they receive. These currents can be small requiring low noise preamplification. One way to amplify the current while simultaneously converting it to a voltage is to force the current to charge a capacitor. This can be accomplished by placing a low value capacitor across the negative feedback pin to the output pin on a suitable operational amplifier or across a discrete transistor preamplifier. The simple formula is: V = (Integral of I over time)/C
The smaller C is, the larger V will be for a given current pulse amplitude or duration. C = 1 pF will provide good preamplification for current pulses on the order of 100 nA and time durations of 100s of nanoseconds.
2006-07-08 18:43:27 · answer #1 · answered by SkyWayGuy 3 · 1⤊ 0⤋
They are mostly used with IC's to either hold a small charge or to filter out interference in the circuit by jumpering it between the postive and negative of the IC. This is a very popular thing in digital electronic devises due to high frequency interference.
2006-07-02 05:24:20 · answer #2 · answered by jamey.moore@sbcglobal.net 1 · 0⤊ 0⤋
Although femtofarads are usually used in IC circuits all capacitors have a use, at different frequencies etc
2006-07-02 03:45:14 · answer #3 · answered by Robert B 4 · 0⤊ 0⤋
Logic circuits.
2006-07-02 03:29:36 · answer #4 · answered by ag_iitkgp 7 · 0⤊ 0⤋
charge pumps, rail stabilizers... you name it.
2006-07-02 03:30:45 · answer #5 · answered by Anonymous · 0⤊ 0⤋