9.1. Basic Current Source
An example of a current source based on PMOS transistors is shown here in Fig. 9.1. It consists of the reference circuit, consisting of transistor M3 and bias resistor Rbias. The reference-circuit transistor is diode connected. The induced VSG3 = VSD3 is applied to the current-source transistor M2. Thus, the drain current, or current-source current of M2 is the mirror of the reference current. In an integrated circuit, any number of current sources can be referenced to the reference current or voltage. Current ratios are implemented with the selection of the relative gate widths of the transistors.
Figure 9.1. PMOS current source. The current set up by the reference circuit of M3 and Rbias is mirrored as the current ...
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