BRASILIA, June 25 (Reuters) - Brazil is making progress on studies into launching a digital currency but there are several challenges to overcome, including technology and difficulty in ensuring uniformity across the world, central bank chief Roberto Campos Neto said on Friday. In a live event hosted by the Brazilian banking association Febraban, Campos Neto said the idea of a digital currency still throws up more questions than answers, but he hoped to announce a more concrete time frame later this year. (Reporting by Jamie McGeever and Gabriel Ponte Editing by Chris Reese) Our Standards: The Thomson Reuters Trust Principles.