Browse Prior Art Database

Low Current Source Building Block

IP.com Disclosure Number: IPCOM000089105D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Maillet, JC: AUTHOR

Abstract

The drawing shows a simple integrated circuit which allows low currents to be generated from a master high current source wherein the silicon area required on the chip is low. This circuit takes advantage of the high ratio accuracy of ion-implanted resistors.

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Low Current Source Building Block

The drawing shows a simple integrated circuit which allows low currents to be generated from a master high current source wherein the silicon area required on the chip is low. This circuit takes advantage of the high ratio accuracy of ion- implanted resistors.

The circuit is composed of master current sourcel and a plurality of slave sources. Only two slave sources 2 and 3 are represented in the drawing.

Master current source 1 comprises transistors T1 and T2, resistor R, and resistors R1 and R2 forming a voltage divider. Slave sources 2 and 3 comprise transistor T3 and T4 having their bases connected to common node A of resistors R1 and R2.

Transistors T1 and T2 form an amplifier subsystem with total feedback. Thus, the base current of transistor T2 and the current through resistor R1 are supplied by transistor T1. Hence, if the beta factor of transistor T1 is fairly high, the collector current of T2 will be nearly equal to I(REF) and the mathematical expression of current i in slave sources 2 and 3 can be calculated as follows: V(beT3) = V(beT2)R2/ (R1 R2) (1). (kT/q) Log (i/I(o)) = R2/(R1 R2).(kT/q).Log(I(REF)/I(o)) (2). where I(o) is the saturating current of the emitter base junction of the transistors which are similar. Let R2/(R1 R2) = alpha Then i = (I(REF))/alpha/.I(o)/(1-alpha)/ (3).

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