Current Sources and Voltage References

156

Using the JFET as a current source

the zero TC point, then back to the origin at 0. Where it intersects with the curves will

determine the V

GS

and I

D

.

Knowing where the zero TC point is allows one to tailor the circuit to have a positive

tempco, by operating the drain current

above

I

DZ

, or to have a negative tempco, by

operating the drain current

below

I

DZ

(see Figure 6.16B). Normally one will have to

build a circuit, then test it under extended temperature conditions (in an accurate

oven), logging the results on a graph. Once you have some data recorded and

graphed, you can then compare it with your initial design calculations. This is not the ...