High voltage limiter

Hi,

I need to design a high gain receiver that must be able to withstand (block) high voltage (350 V) pulses (the receiver must amplify the very small signals that follow this pulse).

Any idea on how to block the high voltage pulses in order to protect the receiver? Originaly I used a resistor and a pair of diodes, but the resistor generates too much thermal noise that gets amplified in the receiver.

Thanks,

cyberblak

What about using Zener Diodes only ! or using Filter to remove these spikes !

I want to know what is ur Application in order to specify more ur problem ?

In fact this receivers will receive very high voltage pulses (~350V) followed by a series of small signal pulses (~100uV - 500mV).

I need to detect the small signal pulses, but of course I have to block the high amplitude pulses.

A zener diode without a current limiting resistor would create a short-circuit... The amplifier that generates the high-voltage pulses wouldn't like to have its output short-circuited.

I can't filter the pulses also since I don't want to filter out the signal itself.

Thanks anyway,

cyberblak

What about your operating frequency , Are both high & low amplitide pulses same freq. or not ?

What about using Comparator , and set suitable threshold level ?

Maybe the value of a resistor that you used in the input-limitter circuit was to high ..
In many sonar/echosounder applications they use a metalfilm resistor (470-680Ω) followed by two small signal pulse diodes (1N914 - 1N4148) and it seems to work fine ..

Regards,
IanP

Thanks to all for your replies...

The frequency involved is around 35 MHz, so this must be quite wideband.

IanP : Good suggestion, however the noise budget is soooo low. Even a 50 ohms series resistor (which makes the high voltage amplifier whines a lot) is too high a value. I initialy used 180 ohms with the two antiparallel diodes.

resistor noise = sqrt(4kTR) = 0.98nV/rtHz => 34,2 mV peak to peak @ 60 dB, 35 MHz

And that is only accounting for the resistor thermal noise... So any idea on how to avoid this resistor is more than welcome!