Electronics Engineering Question:

Fixed bias circuits get their bias voltages from independently designed reference voltage sources (or even something as simple as a voltage divider). Often is the case that the bias may be left for the end-user to give some control over the operation point of the circuit.

Self biased circuits get their bias voltages from the circuit itself, often in the form of a negative feedback. This is very useful when a circuit is extremely sensitive to bias points and it becomes impractical to provide external biases that are correct to very high accuracies. This can happen in high gain amplifiers with very high impedance output nodes, such as a common source amplifier with an active load. The operation of the circuit dependson the bias of the active load. It would therefore be desirable to sacrifice some of this gain by providing a negative feedback from the output to the gate of the active load. This way, you wont have to bias the circuit yourself, but will lose some of the gain of the circuit as a price.