Current Biasing Circuit
Original Publication Date: 1988-Dec-01
Included in the Prior Art Database: 2005-Feb-15
A current biasing circuit is fully integrated on one chip to provide a constant current which is independent of variations in temperature and supply voltage. The temperature-compensated current is produced by adding up current having a positive temperature coefficient (TC) and current having a negative TC. The circuit exemplifying the technique is in bipolar-field-effect transistor (Bi-FET) technology. Referring to the figure, the emitter area of bipolar transistor T6 is n times larger than the emitter area of bipolar transistor T7. P-type FETs T1 and T2 form a current mirror. N-type FET T4 provides base current for bipolar transistors T6 and T7 so that a negative feedback loop is formed between transistors T1 and T2, and T6 and T7. Note that, because the circuit is self-biased, a start-up circuit is required.