Can I set up a Trial-period that defaults to Free without entering payment info?

I know I can set up different levels of membership, and there are trial periods for paid levels. But is payment info always required before a trial period begins?

Basically I want to offer a free membership (limited access to content) and a paid one (full access to content). But I want the free version to have the first 7 days with all the benefits of the paid one (full access), and then revert to being free membership when the week is over. But I don't want people to have to enter credit card details at any time. They ONLY need to do that if they want to upgrade to the paid membership.

So is this possible? I know how to make a trial period for a paid plan, but I think that requires people to enter payment details before they join, correct? (And they are only charged when the trial period is over, and they haven't cancelled).

I'd like a way for people to get full access for a week without the need for ever entering card details, and if they don't upgrade they are just free (limited access) members after that.
Let me know if this is doable!!