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T/2/L Controlled Current Source

IP.com Disclosure Number: IPCOM000077669D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Dorler, JA: AUTHOR [+2]

Abstract

This circuit provides a controllable constant-current source for T/2/L application. When the T/2/L circuit is turned on, the circuit provides constant-current control so as to turn on and control a plurality of current sources. If the T/2/L circuit is turned off, the constant-current control and the plurality of current sources are likewise turned off. Accordingly, the plurality of current sources can be selectively turned on and off. Moreover, the circuit provides an active pull up in order to rapidly restore the lines when going from an on to an off state.

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T/2/L Controlled Current Source

This circuit provides a controllable constant-current source for T/2/L application. When the T/2/L circuit is turned on, the circuit provides constant- current control so as to turn on and control a plurality of current sources. If the T/2/L circuit is turned off, the constant-current control and the plurality of current sources are likewise turned off. Accordingly, the plurality of current sources can be selectively turned on and off. Moreover, the circuit provides an active pull up in order to rapidly restore the lines when going from an on to an off state.

The circuit receives an input signal at terminal 10. Transistor T1, Schottky barrier diodes D1, D2, D3, and resistors R1 and R2, form the T/2/L portion of the circuit. The constant-current control section is constituted by transistor T3 and R3. Transistor T2 and diodes D5 and D7 comprise the active pull up portion of the circuit. The plurality of constant-current sources are each comprised of transistor T4 and diode D4 . . ., transistors Tnth and diode Dnth.

Operationally, when the input to diode D1 is more positive than +2.0 volts, transistor T1 turns on. The emitter current of transistor T1 is established by resistors R1 and R2. The emitter current of T1 is equal to I(ET3) + I(BT4) + I(D4) + I(BTnth) +I(Dnth). When I(ET3) is set to 1.0 ma, for example, the VBE drop of T3 controls the amount of current through T4 and Tnth which are the current sources. That is to say, I(ET3)...