IC Current Source
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
AbstractNPN transistors T1-TN are connected in common collector configurations as integrated circuit (IC) current sources in lieu of their being connected in common emitter configurations as is done in another known circuit.
IC Current Source
NPN transistors T1-TN are connected in common collector configurations as integrated circuit (IC) current sources in lieu of their being connected in common emitter configurations as is done in another known circuit.
Transistor T1 in coaction with emitter follower TE provides a reference source for the subsequent transistors T2-TN. The bases of transistors T1-TN are connected to a common reference distribution bus AB. Each subsequent transistor T2-TN is connected to a cascode current stage, cf. switch TN and typical cascode stage 10, for example.
With the NPN transistors T1-TN so inverted, ringing caused by emitter follower TE is substantially eliminated as the beta rolloff of T1-TN is at a lower frequency than TE. Also, because the emitter to base capacitance (CEB) is much less than the collector to base capacitance (CCB), which in turn is much less than the collector to substrate capacitance (CCS), the emitters of Q1 and Q2 of each individual stage 10 see much less capacitance, resulting in minimized ringing in the collector outputs of Q1 and Q2, as is not the case when the emitters of T1-TN are connected to ground and the collectors of T2-TN are connected to the emitters of Q1-Q2 as is done in the aforementioned known circuit. The present inverted configuration also couples less noise into the reference distribution bus AB than does the known circuit.