overdrive recovery

[[email protected]]

Hi all,
I have a multistage amplifier intended to measure small (uVs) signal.
And a 100 volt spike saturates the amplifier. I am searching for low
capacitance fast recovery diodes as my option to clamp the voltage
after the first stage to few 100 mVs to improve my overdrive recovery
time. I have some Schottky diodes but want to see if somebody can
suggest better ones.
thank you

 

[Eeyore]

Hi all,
I have a multistage amplifier intended to measure small (uVs) signal.
And a 100 volt spike saturates the amplifier. I am searching for low
capacitance fast recovery diodes as my option to clamp the voltage
after the first stage to few 100 mVs to improve my overdrive recovery
time. I have some Schottky diodes but want to see if somebody can
suggest better ones.

Have you considered active clamping using a transistor ?

Graham

 

[MooseFET]

Have you considered active clamping using a transistor ?

I'll second that comment and add that a circuit that forces the later
sections of the amplifier to be in the linear span further improves
the recovery. Heres a very simple circuit that sort of shows the
idea:


In ------+------/\/\------------+---------------+-------- Out
! ! !
! !/e !/e
---/\/\-+------------! NPN VB----! PNP
! !\ Q1 !\ Q2
VB ! !
GND GND

If "In" goes more than 0.7V away from ground either Q1 or Q2 will turn
on and force "Out" to ground.

 

[[email protected]]

I have found these TVS ESD9L5.0S-D from one semiconductor. Low
capactiance and fast recovery, may be i can put a couple of these on
each line.
http://www.onsemi.com/pub/Collateral/ESD9L5.0S-D.PDF

 

[[email protected]]

Have you considered active clamping using a transistor ?

Thank you Eeyore and Moosfet.
Yes that do appear fine, i was getting lazy and trying to use the same
PCB by sticking a few xtra diodes. Though please tell me what would be
an advantage compared to a pair of TVS?

 

[Eeyore]

Have you considered active clamping using a transistor ?

Thank you Eeyore and Moosfet.
Yes that do appear fine, i was getting lazy and trying to use the same
PCB by sticking a few xtra diodes. Though please tell me what would be
an advantage compared to a pair of TVS?

By adjusting the bias voltage on the first transistor in MooseFET's post,
e.g. biasing it above or below ground you can adjust the clamping point.
It will go easily as low as 100mV.

Graham

 

[MooseFET]

By adjusting the bias voltage on the first transistor in MooseFET's post,
e.g. biasing it above or below ground you can adjust the clamping point.
It will go easily as low as 100mV.

To make that a little clearer: Give each transistor its own base
resistor and also run a resistor from the supplies to the bases.
Biasing the the voltage on the base controls the point where it
clamps. Hooking the collectors to voltages other than ground controls
both the point where it clamps and the voltage it pulls to when
activated.