Function generator for OFDM signal
OFDM is a very inherently digital thing. 

It's technically generated by applying a DFT (discrete fourier transform, as in digital) to transmit symbol vectors (symbols==digital transmission).

Spectrally, it's an array of sinc-shaped subcarriers places such that the  zeros of the spectral shape of each carrier lies on all the other carriers center frequencies.

The only way to produce such sincs is (fourier transform!) to produce coherent rectangular signals on each subcarrier of the right period. 

That is 100% identical to saying that you need a digital (as in: time discrete) circuit.

So, whatever circuit produces as spectral shape that is like that of an OFDM signal  is a digital circuit. You can't build an analog OFDM.

A "summation of sinusoids", as you mention in one of your comments, is not remotely similar to OFDM – neither from a spectral in-band point of view (OFDM's everything but zero between center of carriers) nor from a larger bandwidth point of view – OFDM has severe sidelobes – nor from a Peak-to-Average-Power-Ratio – OFDM is known for leading to very non-constant time-signal envelope, very much unlike your simple array of sinusoid. 


  And the ideal scenario would be if I can generate an analog signal based on a given digital input.


Buy or build an SDR device, and transmit digitally generated OFDM signals. That's what SDR is all about: being able to describe the analog waveform in digital domain.