Browse Prior Art Database

Wide-Temperature-Range Current-Source Generator

IP.com Disclosure Number: IPCOM000039159D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Ashton, GJ: AUTHOR [+2]

Abstract

A technique is described to overcome the failure of current-source generators to compensate at low temperatures due to the limited power supply differential available. With previous compensated current- source emitter-follower (CCSEF) reference current-source generators, (Image Omitted) the generator compensated to mid-swing as a reference. The new design regulates to an attenuated value of reference to avoid driving the differential amplifier into the saturated region. The circuit schematic of the previous reference current source of Vcs is given in Fig. 1. This is to be operated at Vcc = 1.35 V, Vee = 1.7 V and Vr = 0 V nominally. For worst-case environmental conditions Vcc approaches 1.188 V, and Vr approaches 0.09 V.

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Wide-Temperature-Range Current-Source Generator

A technique is described to overcome the failure of current-source generators to compensate at low temperatures due to the limited power supply differential available. With previous compensated current- source emitter-follower (CCSEF) reference current-source generators,

(Image Omitted)

the generator compensated to mid-swing as a reference. The new design regulates to an attenuated value of reference to avoid driving the differential amplifier into the saturated region. The circuit schematic of the previous reference current source of Vcs is given in Fig. 1. This is to be operated at Vcc =
1.35 V, Vee = 1.7 V and Vr = 0 V nominally. For worst-case environmental conditions Vcc approaches 1.188 V, and Vr approaches 0.09 V. This causes the upper level noise margin to be at its worst and the circuit operation of the generator will be out of control at a junction temperature lower than 40oC when used for semiconductor applications. This is because at temperatures lower than 40oC the Vbe drop of Ts can cause Vs to be limited to a negative value. The worst-case Vr can be 0.09 positive. With the above conditions, the operational or sense amplifier in the control loop loses its defined function. The control loop function is indicated in Fig. 2. The proposed difference sensing scheme is shown in Fig. 3, wherein Vs only tends to be negative. As soon as this occurs, VSl begins to move positively, thereby narrowing the drop of (...