I created a I/V stage with amplifier for my DAC project. An excerpt of the circuit can be seen in the attached picture in the "Device under test" part. The DAC has a 3.9mA pp current output, which I convert to voltage using a high precision resistor (R302).
I want to draw an approximate bode plot of the circuit using my function generator, whose output is a voltage. I have studied some literature, and I know that using opamps and transistors is possible to create very precise voltage controlled current sources, but before proceeding with building another device, I tried to find a easier solution by myself.
What I need is a current which is more or less the same my DAC will give as output (circa 4mA). My idea was to just use the Ohm law V = RI with the intuition (which may be wrong, since I am quite a beginner) that if I put the low input resistor in series with a much bigger one (R301 in the schematic), the input current will be dictated almost only by the latter. In other words, the small resistor almost disappears when put in series with a much bigger one. This way, I could generate the needed current by just putting this big resistor in series with the input of my circuit, and trimming the output voltage of my functon generator.