Low Voltage limiter circuit with fast recovery time

Question

Hello I am having trouble building/finding parts for a circuit that I need to limit the peak voltage of a signal coming from a photodetector.

My problem is that an amplifier I am using will not tolerate a signal above 200mV without damaging the device. My signal is a photomultiplier PL decay curve with a 100-200mV plus peak amplitude, whereas the part of the signal we are trying to observe is four decades lower in the long tail of the decay, hence our needed amplification (it's near the noise of the instruments pre amplification).

My other problem is that the pulse which this 100-200mV peak is part of, is rather fast (50ns). From researching various diodes I've been learning that a schottky diode is either fast recovery or have a low voltage cutoff (at least from what I have seen at mouser and digikey), but not both.

My plan was to build a intermediate circuit between the photodetector and amplifier that cuts off any voltages above, lets say 150mV to be safe, but I am unsure whether or not this is possible giving how low that cutoff voltage is as well as how fast this pulse is.

I welcome all suggestions to this problem, for I am stuck and questioning if this is possible with a basic diode circuit or if another design altogether is needed.

Thank you.

Adam

Answer 1

The gate-to-channel junction of a JFET is sometimes used as a low-capacitance clamp diode in high-speed applications. While this normally has a forward voltage drop on the order of 0.65 V, you can clamp at lower voltages by applying a negative bias to the channel:

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

I've used a MAX3762 limiting amplifier to cut down the dynamic range of optical signals. I've used it at 660 Mbps: -

From memory it starts to limit at about 4 mV