file_exists() question

Can anyone tell me why this code does not return true when the file in the directory cherpdocs/ with the file (which I see as being there) does exist? if(file_exists('cherpdocs/$annrow[id].doc')){

        echo "<br /><a href=\"cherpdocs/$annrow[id].doc\">Funding details paper</a>";

} This is a path relative to the file calling it, should it be otherwise? Thanks Charles