Current Sources and Voltage References

Current scaling

Using BJTs to Create Current Sources

95

In this circuit the output current, I

C2

, is determined by:

To further illustrate the importance of the PNP multiple cascode circuit, Figure 4.33

shows the biasing and input circuitry for a typical bipolar voltage-feedback op amp,

using a PMOS transistor pair input stage. As you will recognize, the input stage relies on

a PNP multiple cascode, as well as an NPN current mirror using emitter degeneration.

4.8 Current scaling

With the exception of the Widlar and the Wyatt current sources, up until now we have

looked at current sources that generate input-to-output currents in a 1:1 ratio, but it is ...