There are two main types of current sources: independent and dependent. An independent current source maintains a constant current with no external influence. A dependent source will control current based on an external value, such as another current or voltage elsewhere in the circuit. There are many implementations for current sources, each with their own benefits. A very simple current source can be created by connecting the gate to the source of a FET. In this configuration, the current is essentially constant once the drain-source voltage reaches a value to saturate the device. Other implementations can include negative feedback and temperature compensation to more precisely control the current over real-world conditions. In ASIC implementations it is common to use the constant voltage of a bandgap reference in a circuit to create a reference current which can then be mirrored to create other current source(s).
As experts in mixed-signal ASIC design, Triad engineers can implement precision control of currents either internal to the ASIC or externally. Applications may include a high-speed current-steering DAC as an internal function or control of a photo-diode/LED current as an external function.