low noise amplifier for high impedance source
- From: archiees@xxxxxxxxx
- Date: 15 Oct 2006 18:50:31 -0700
Hello everyone,
I am a student who has been working on a low noise preamplifier for a
high impedance current source. I have put the model of the detection
circuit here:
http://img146.imageshack.us/img146/9748/detectmodelid8.jpg
Its a differential ac current source with an instrinsic capacitance ~
20pF on each side. I use 1M ohm resistors to bias my input JFETs.
The bandwidth i need is only from 10 Khz to couple of MHz.
In my learning process, i have realized few things such as selecting
JFETs as my input transistors for low leekage hence low input current
noise. Maximise the value of input resistor without disturbing the bias
of the input JFETs. However i still have couple of unanswered
questions:
1. How does the Cin of the JFETs effect the signal to noise. do i have
to match the input capacitance of the JFETs to the source capacitance
for minimum noise? How about if i put multiple JFETs in parallel to
reduce input voltage noise - do i have to revise my JFETs selection in
terms of input capacitance?
2. While evaluating the performance of the designed amplifier can i
neglect the equivalent input current noise, as i am using the JFETs?
3. Are there any good review articles or texts for low noise
preamplifier design (for capacitive sensors).
Please help!
thanks
-arch
.
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