Nginx sub_filter syntax: sub_filter string replacement;

A variable in Nginx is set using the operand $: set $a 'Hello World';

When a $ is present sub_filter String but not a variable, Nginx will not allow the String e.g.

sub_filter 'data-ng-click="$ctrl.goto 'onclick="location.href=';

I am sure there is a "work around" so that $ctrl is not seen as a variable and just part of the String to be replaced?

Any help would be appreciated