I'm wondering how to make a current source with two different frequency combined signals( i.e. I1sinw1t + I2sinw2t )
I was first thinking of using an adder with op-amps but it seems to be wrong.
Can anyone tell me the circuitry or at least give some hints?
Thanks in advance.

 

There are a number of ways and a big determiner is going to be what are the frequencies and amplitudes (both voltage and current) that we are talking about. Assuming that we are talking pretty low frequency and only moderate power, I would recommend a block diagram that would look like the following:

A circuit that produces a sinusoidal voltage signal of a constant amplitude but that allows you to vary the frequency (if you want to be able to vary that, otherwise just fixed at a given frequency).

Follow that by a circuit that you can control the gain with so that you can vary the amplitude of the sinusoid from the first circuit.

Now make two of these.

Now make a voltage summing circuit and apply the outputs from both of the gain circuits from above as the inputs. The output of this is now a voltage signal that is the sum of two (and you could modify it to use more) signals each of which you can control the frequency and amplitude of.

Now follow that circuit with a voltage to current converter.

QED