You are right not a fully qualified question. This will be an input stage to my DSO. I want to measure higher voltage than 5V or 50V. I decided to extend the input voltage range to 350V (peak). Currently, the input bandwith roughly 1Mhz (2MSPS). Thus, I think the input bandwith can about 1Mhz .
Generally the transformer is a good choice, but in this case I think it doesn't have enough bandwith. Am I correct?
There is no critical current recuirement, it have to drive just the next amplifier stage. Thats all.
If I would know how to design this stage, later on I can extend its bandwith upper to fit my next design requirements.
It sounds like all you need is a conventional x10 scope probe - either single ended or differential design. Your 350V would then be scaled to 35V, and would easily be measurable on your 50V input attenuation setting.