VLSI Interview Questions - I

Lets start with simple questions. There will be a maximum of 3 questions per post.

Q1: What is the difference between SRAM and DRAM ?

A: Both are volatile memories.(data is lost when powered off) But, SRAM need not be periodically refreshed as compared to DRAM. DRAM stores each bit of data in a separate capacitor. It can either be charged or discharged. (either to 1 or 0).

Since capacitor leak charge, the data fades unless the capacitor is refreshed periodically.
This marks the difference between SRAM and DRAM.

Q2: Design a posedge/negedge/edge dectector circuit ?

A: Basically, edge detector circuits are used during bit synchronisation from one clock domain to the other. Below circuit will explain in detail:

Posedge detection circuit:

Below is the Waveform explaining explaining the circuit:

Negedge Detection circuit: 

Below is the Waveform explaining the circuit:

Edge detection circuit:

Below is the Waveform explaining the cicuit: