hi,

see if you want to do phd in electronics or any other engineering related subjects you will not allow to do so as you dont have electronics or electrical or mechanical related back ground.. right now nano technology , artificial intelligence , power electronics and devices are demanding topics for phd in technical domain. you can do phd in following subjects as per the different universities eligibility criteria. however there is chances to do phd in mathematics related areas.

Human Computer Interaction

Empirical Studies of Software Development

Diagrammatic Reasoning and Understanding

Dynamic models for problem tangles

Natural Language Processing

Enterprise Security Modelling and Analytics