NVIDIA interview questions

I got a call from HR. He asked me for suitable schedule for telephonic discussion. We agreed for a slot. No sign of call after 25 minutes the time of interview, when I called HR and ask him to remind interviewer. He asked me wait for 10 mins and I waited another 20 minutes without any response. I again called HR myself and asked him to reschedule as I was getting late for office. HR told me that he is going to reschedule. But again I did not receive any for a week. I tried to contact them via phone and email. But they didn't response any of it. My message to recruitment team. Forgot professionalism, get some courtsy first. Most terrible experience ever.

they asked questions regarding basic op amps and digital to analog converter as well as analog to digital converter. and the quantization noise in the ADC. Also there was questions regarding frequency response.