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Programmable Driver Output Stage

IP.com Disclosure Number: IPCOM000074352D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Hutson, DJ: AUTHOR

Abstract

This circuit minimizes initial transient drift in a conventional emitter-follower circuit when it is used as an output stage of a programmable high-speed driver. Normally, the V(BE) of the output transistor will have an initial transient drift caused by changes in power dissipation when the input voltage is switched from one level to another. When a large signal swing is applied to the node labeled V IN, the signal propagates to the bases of T1 and T2 and out the emitters of these transistors. The value of the voltage level at the base of T1 will be V' - V(D)1 while the value of the voltage level at the collector of T1 will be V - R2I(B)2 - V(BE)2. A V(CB) will be established on T1 which is just enough to keep T1 out of saturation.

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Programmable Driver Output Stage

This circuit minimizes initial transient drift in a conventional emitter-follower circuit when it is used as an output stage of a programmable high-speed driver. Normally, the V(BE) of the output transistor will have an initial transient drift caused by changes in power dissipation when the input voltage is switched from one level to another. When a large signal swing is applied to the node labeled V IN, the signal propagates to the bases of T1 and T2 and out the emitters of these transistors. The value of the voltage level at the base of T1 will be V' - V(D)1 while the value of the voltage level at the collector of T1 will be V - R2I(B)2 - V(BE)2. A V(CB) will be established on T1 which is just enough to keep T1 out of saturation. This condition will exist regardless of the value of the input voltage within the operating range of the circuit. Therefore, the power dissipated by T1 will be minimum and relatively constant throughout the operating range of the circuit. The V(BE)1 junction temperature will be relatively constant and drift due to a change in power levels, when the input voltage is switched from one state to another will be virtually eliminated. The change in V(BE)1 due to changes in ambient still exist, however, but are insignificant in this application. The main power dissipation has been transferred to T2 which has very little effect on the output voltage characteristic. R1 and R2 are chosen with regard to transient ...