Any ideas for how to estimate resistor values for the current source?

 

What is the transistor gain? What values would set the bias for 30uA of current?

Think of ground and the point above Rc as +V Sources, and the - V as ground if you are having problems with equations.

 

Assuming Beta=100, I did some calculations but ended up using some trial and error with the emitter resistor (Re) to get the current right. With respect to the schematic I posted on page 2: Re=120k, R1=510k, R2=360k. From the simulation I just found that Beta is actually 200.

*(For all of these results I'm using a sine wave source @ 40mVpp, 1000Hz)
- Vout in diff.-mode = 6.6 Vpp
- Vout in comm.-mode = .0001 Vpp (this wave is centered around 4.73V)
- Ic1,2 = 14.64uA
- Io = 29.41uA (current source collector current)

There's no clipping either!
One thing I'm concerned about is the common-mode voltage level (i guess it's the DC level?), although it's peak to peak voltage is very small. Is this a problem?

I'm using LT Spice to simulate. For testing the common-mode I make the two sinewave sources the same polarity and for diff-mode, opposite polarity (like what I'll be doing when testing the actual circuit).

 

Post the plots of input/output when in common mode to see what the gain is.

maybe try a small bias voltage to both sides to see how it handles that as well.

 

I finished the project and met all requirements! Thanks for the help! I'll try to get my final results and plots up soon.