Equal current generating circuit - has each output driven by Darlington pair connected to differential inputs of long-tailed pair

摘要

A transistor circuit is used for generating a set of currents which are accurately set equal to each other. It is for use in digital to analogue converters, and uses sensitive differential amplifiers connected in a ring formation. Each current output (In, In-1 .....) is driven by a Darlington pair (T9, T10, T11, T12.....) of n-p-n transistors. These are connected to the differential inputs of long tailed pair differential amplifiers consisting of n-p-n transistor pairs (T2, T3, T4, T5)....., T8, T1) and associated resistors (R1, R2....R8). Each differential amplifier equalises the current produced at that stage with the neighbouring stage, provided the resistances in the two stages are equal. The ring formation guarantees the equality of the first and last stages.