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Low-Noise Front End Protection

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Evan.Cornell:
Any recommendations for low-noise/leakage protection diodes for non-inverting input of LNA?

Kleinstein:
A common modern low leakage diode is BAV199.

If tested low leakage is required, 1N4117 or 4118  JFETs are an option too.

Another point is keeping the temperature low and the voltage small, by bootstrapping the diodes.

Usually the diodes are not causing much noise, but they can cause leakage - so it depends on the impedance level.

David Hess:
For RF, it is common to use microwave schottky or PIN diodes for input protection because they have lower capacitance than common diodes which would otherwise be suitable.  You said LNA so I assume it is an RF application.

Evan.Cornell:
Not RF, signal range is only up to 200kHz. I am mostly concerned about noise contributions of any amplifier input protection circuitry to the actual input signal.

David Hess:
Then Kleinstein covered two of the good options, low leakage BAV199 diodes which are not tested and low leakage JFETs like the 2N4117 which are.  I like using 2N3904 emitter-base or base-collector junctions myself but they also are not tested for low leakage so you have to do that yourself.  Any of these options can be good to 100s of MHz.

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