BUF634: Glitch in the output of BUF634P

Probably hitting a slew limit, try low pass filtering your input signal to slow its edge rate down, 

Hi Michael,

My signal is 33Khz and I set the BW to 180Mhz(30 MHz to 180 MHz).

May I know how slew issue is occuring here.

Regards

HARI

okay,will check it.

Hello Hari,

For new designs, it is recommended to use the BUF634A, a drop-in replacement part with upgraded functionality.

Please let us know when you are able to investigate Michael's recommendations.  Also, I can help you order an EVM if you require assistance.

Best,

Alec

Hi Team,

I measured the slew rate of my source(TEKTRONIX FUNCTION Gen).Please see below

it is coming 38MV/s.

if I convert I will get 38V/uS(Please confirm).

Regards

HARI

Hi Hari,

don't feel offended, but it's impossible to carry out representative measurements with the BUF634 sitting on a simple bread board. A solid ground plane is a must when handling this ultra-fast 2000V/µs buffer.

Another issue is cable termination. You must provide proper cable termination at the input and output of BUF634. And the BUF634 must sit closest to the input and output connectors. If not, you may additionally need to provide microstrip or stripline technique between the connectors and the BUF634. Simple centimeter long wires as your setup shows will not do the trick and may give totally weird results.

Kai

Hi Kai,

Your suggestions are always valuable for a novice like me.I will never offended.

May I know what you mean by cable termination.

Do I need to keep 50 ohm series resistor at the input of the buffer.

Michael told me to measure the slew rate of the input source(Function Generator).I put it in the post may I know is it correct

Regards

HARI

Hello Hari,

Working with the BUF634(A) is going to require learning about high speed layout techniques and terminology.  As a starting point, there is this TI document on high speed layout.  Termination refers to the characteristic impedance of the traces and the impedances present at the buffer inputs and any connectors/connected circuitry.  Section 1.3.2 is a good start for learning about termination, in the linked document. 

Terminating the input of the BUF634(A) into a poorly-selected or fluctuating impedance will result in poor behavior.  Most TI product datasheets include descriptions of the electrical characteristics, as well as graphs with various impact of the available choices.  Many datasheets contain a short but relevant layout section as well. 

While it is quick for obtaining a result, the results from a perf-board/proto-board setup for a high speed buffer will be incorrect, weird, and/or misleading.  I recommend either the use of the BUF634AEVM for buffer evaluation, or the use of high speed layout principles on a PCB.  If you are not as familiar with designing PCBs or designing for high speed devices, there are other strong resources available online from PCB vendors & educational sources.  

If you decide you would like to utilize an EVM, please send me a private message and I can assist you with that operation.

Otherwise, please be patient with yourself and your design, as high speed layout and PCB design is not a 'learn it in one day' craft.  Kai & Michael have strong experience in this area, but you may find you need to do learning offline from the forum.  We are here to help, but sometimes we assign homework or readings .

Best,

Alec

Hi Alec,

Regarding EVM ,I will check with my management and let you know.

My office is located in India.Hope that won't an issue.

Regards

HARI

Hello Hari,

I await your response; I will confirm with my team on my recommendations.

Best,

Alec

Hi Kai,

Thank you very much

Regards

HARi