Current Mode Stimulator for High Current

[florescent]

Dear All

I am designing a stimulator that can inject a steady 5mA. To be independent on the load impedance, a current mode stimulator has been chosen for my design. I have researched and designed five different circuits, and the attached one is the best in results so far.

In my application, the load impedance (at this moment, resistance only) can be varied upto 1kohm. The 5mA current should be steady under this load variation.

The results from this circuit attached also. The trade-off, as you can see, is the amplitude of the current vs load resistance. I can't set the circuit that provides around 5mA with upto 1kohm.

The second concern is that I prefer to have such a circuit whose load resistance is at the ground, not on the VDD. In this way, I don't need to have a virtual ground.

I would really appreciate for your comments or suggestions on other circuits.

Thank you for reading

 

[KerimF]

Do you mean if on, the output current should be 5mA then if off, it becomes zero... right?
By the way, which is the maximum resistance of the load you look for... 1K? This means the supply should be 5mA x 1K = 5V plus the bias voltage(s) to keep the active device(s) in their linear region. Do you have an idea on the actual Vdd value?

 

[florescent]

Thank you for your reply KerimF

All your assumptions are right

The simulation results I attached are by 3.3V of VDD

 

[KerimF]

For 5mA and 1K, the voltage drop is 5V on the load while your supply is just 3.3 ! Neglecting the rest of the circuit, from where the load can get the extra 1.7V in your opinion.

Kerim

Added:
This means if you cannot increase Vdd then, I am afraid, you need to be content with a lower current or lower value for the load (its maximum).