Wilson (Wilson) constant current source circuit characteristics and analysis

Wilson constant current source characteristics

As shown in Figure 2.2-4. Due to the effect of negative feedback, the circuit has high output impedance and good constant current characteristics.

The output impedance of this circuit can also be calculated by the AC small signal equivalent circuit ro without considering M 1 In the case of tube substrate bias effect, ro can be written as:

If assuming And , then the formula (2.2-5) can be written as:

The formula (2.2-6) is the same as the formula (2.2-4). Therefore, the Wilson constant current source also has a large output impedance.

In Figure 2.2-4, the drain-source voltages of the M: and Ma tubes are different. To make them the same, MOS diode M. can be introduced. The circuit form is shown in the figure Shown in 2.2-5. Compared with Figure 2.2-4, this circuit has better constant current characteristics, so the circle 2.2-5 constant current source circuit is an improved Wilson constant current source circuit .

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