Hi guys

if i want to clamp a 10MHz, 2V p-p sinusoidal signal at +-400mV, what is the easiest way of doing this?

At the moment i am using the properties of diodes (1N4148, 0.7V volt drop), which succesfully clamp the signal @ +-0.7V. but it is stll higher than the siganl that i want (+-0.4V)

I am now thinking using some fast schottky diodes, which has got a lower voltage drop. But i do not know what other schottky diodes are availabe? (The only schottky diode that i know is 1N5819...)

Thanks

 

How about a simple attenuator after the diode clamp?.

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i hav thought about that, but for that way it's going to introduce more phase shift to the output signal...which is what i m trying to avoid...

it will be great if i can clamp the signal in just one stage!

 

And how does a resistive attenuator introduce phase shift?

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Wondered that myself?.

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Hi Hykwei

I was going to ask the same question but you beat me to it.

About the diodes you could use BAT81 . . . 83 or the BAT85 which has
an even lower forward voltage drop. Other possible candidates are
1N5711 & 12 and the 5082-2300, 5082-2800 and 5082-2900.

on1aag.

 

well...that is what i observed from the output of the attenuator...it does introduce more phase shift when i compare the input and output using oscilloscope...

i suppose every components(even resistor) has got internal capacitance, and under a high frequency system (MHz range), those capacitance becomes more significant + introducing phase shift, doesn't it?

This is what i think...please correct me if m wrong!

Thanks

 

Look at how a scope x10 probe works!, or the switched attenuator inside the scope!.

What value resistors were you using, and what were the source and load impedances.

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the resistor value is 20k...is that too large?

The signal comes from a signal generator.

 

Probably far too large, and why only one resistor?, you need two for an attenuator.

Also, are you using a x10 probe on the scope?, the scope capacitance will cause phase shift with your large resistor.

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