a good quatily of IR can give TTL o/p but again at the end the o/p is feed to buffer(say uln2003) to sharp your o/p.. let me expalin this
when ir falls on Rx its conductivity changes, which in turn changes the resistance and we measure the change in voltage. the change in resistance depends on two thing first the amount of IR and second the quality of Rx.
it you have a good quality of IR pair its Tx and Rx efficiency will be higher so it will be able to give TTL o/p but at the end we can be reliable on it. reliable i mean to say it might change voltage from 0-2.5V but micro controller can’t understand 2.5V so we use a buffer at the end.
see the CKT below:-
i tested it and it works, but again you must have a very good quality of IR pair.
the o/p quality also depends on surrounding environment.