creatinga event for textbox click

i have a asp.ne application with few controls., grid , buttons etc
in that i have few textboxes for filter
when we ebter first few characters in textbox & click  a button we get the filtered results
now at present i type in the textbox & then get mouse & click on the button
wht i need is after typing as soon as i press enter that search button shld be clicked
 
 
 
...