THS4052 _Peak Detector

Hello Kanji-san,

This is really strange behavior. I still need some data-points to dig into this further:

1. You mention that V1_Hi = 5V and V1_Lo = 0V. However from the figure it looks like V1_Hi = 0V and V1_Lo = -5V? Can you please calrify.

2. In order to dig deeper, I would like to understand the clamp voltage on each of the diodes shown and any other dc bias voltages. Can you please send me a high resolution picture of bith circuits (OPA2277 and THS4052)

3. When I compare V4 and V5, the signals are inverted. When V5 starts going down, V4 starts going up. This is truly bizarre. Can you remove the clamp on the output of the 2nd THS4052 and check results as well. (May need to remove the ADC to prevent damage).

4. Can you make sure that when probing with a scope, attach a 1K series resistance to the scope probe tip to isolate its capacitance from the opamp terminals and prevent any further interaction.

We are looking to get into the old design database as well to further understand the internal architecture of the device.

-Samir

Dear Samir-san

Thank you for your responce!!

1. You mention that V1_Hi = 5V and V1_Lo = 0V. However from the figure it looks like
V1_Hi = 0V and V1_Lo = -5V? Can you please calrify.

==>

Yes You are correct...

2. In order to dig deeper, I would like to understand the clamp voltage on each of the
diodes shown and any other dc bias voltages.
Can you please send me a high resolution picture of bith circuits (OPA2277 and THS4052)

==>

Thank you for your comment, I attach the schematic again

3. When I compare V4 and V5, the signals are inverted.
When V5 starts going down, V4 starts going up.
This is truly bizarre. Can you remove the clamp on the output of the 2nd THS4052 and
check results as well. (May need to remove the ADC to prevent damage).

==>

I will ask customer, and I will infrom you later

4. Can you make sure that when probing with a scope, attach a 1K series resistance to
the scope  probe tip to isolate its capacitance from the opamp terminals and prevent any
further interaction.

==>

Thank you for your commnet

I will check customer's test method.

Is that mean " Scope== Probe= 1Kohm( in series) == OP amp terminal " using ative probe ?

 Best Regards

Best Regards

Hello Kanji-san,

Thanks for the circuit, it helped me see some of the details a lot better in order to analyze the circuit.

I have been working with the designers to get to the database for the device, however the server has been moved a couple of times and now we cant seem to find the original design. I dont have any EVMs with me currently for testing so I have placed an order for some EVMs. It should be here next week and I can try things on the bench then.

I do think there are stacked diodes on the THS4052 and this is what is causing the circuit the behave the way it does. One thought I have to possibly fix the circuit is to limit the current that can be provided to the clamping diodes internal to the THS4052. However we have to do this without causing any voltage drop at Pin V4 (Pin 7 of the 2nd THS4052). I think the best way to do this is to insert a resistor (say 1k-10k) between Pin 6 of the 2nd THS4052 and Pin2 of the 1st THS4052. We may have to play around with this value of resistance

In addition to this I think we will have to eliminate the 3.3KOhm resistor at pin 7 of the THS4052 as well. The reason for this is that the presence of that resistor can cause the 2nd amplifier of the THS4052 to go open loop when it is providing the current back to the 1st opamp; we want to prevent this from happening and removing the 3.3k will help enable this.

Please let me know if the customer can try this out.

-Samir

Hello

Thank you for your answer!!

According to cstomer, removing the clamp diodes after the 2nd OP amp( THS4052 )

did not fix the problem....

(1)

Also , according to customer, the 3.3Kohm resistor at the 2nd OP amp is used in order to drive ADC properly,

so customer says it can not be removed..... customer says they don't know the meaning of 'Open loop' below .

Would you please let us know the meaning of ' Open Loop'? if available.

~~Your answer~~

that resistor can cause the 2nd amplifier of the THS4052 to

go open loop when it is providing the current back to the 1st opamp;

~~~~~

(2)

Anyway, I found the sample design (TINA  desiged by Mr Neil P Albough /BB ) , attached..

Would you please  let us know how to select the value of  R2 ( 2K ohm ) and C2 (5p )  ?

I could not find any app note for this.

P/S

Customer ( and I ) think if  there were stacked ( 4V ) back to back diode inside of THS4052,

customer and I think this phenomenon is make sense....

Thank you and I am sorry to bother you again..

Best Regards

Dear Samir san

Thank you for your detail desctiption and answer, I appreciate for you

Thanks and with my best regards