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MTL Compatible Current Switch Circuit

IP.com Disclosure Number: IPCOM000086890D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 104K

Publishing Venue

IBM

Related People

Chin, WB: AUTHOR [+2]

Abstract

Fig. 1 shows the merged transistor logic (MTL) current switch circuit. The major components of the circuit comprise devices 6, 6A, 7 and 8. These devices are contained in one isolated collector diffusion. Device 6 is an inversely operated bipolar structure consisting of a base diffusion with the potential of containing more than one emitter contact. The contact to the base diffusion of this device is a logical input to the circuit. The emitter contacts are outputs of the circuit.

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MTL Compatible Current Switch Circuit

Fig. 1 shows the merged transistor logic (MTL) current switch circuit. The major components of the circuit comprise devices 6, 6A, 7 and 8. These devices are contained in one isolated collector diffusion. Device 6 is an inversely operated bipolar structure consisting of a base diffusion with the potential of containing more than one emitter contact. The contact to the base diffusion of this device is a logical input to the circuit. The emitter contacts are outputs of the circuit.

Device 6A (other similar devices can be added) is utilized to provide multiple logical inputs to the current switch structure. The base contacts to these devices serve as logical inputs and the emitter contacts serve as logical outputs when tied to the emitter contacts of device 6. The logical function performed at these dotted emitters is identical to the NOR function of a standard current switch circuit.

Device 7 forms the reference side of the current switch and is identical to device(s) 6 in structure. Its base contact is tied to a reference potential VR.

Device 8, a normally operated NPN transistor contained in the same collector diffusion as devices 6 and 7, functions as a current source. In the circuit shown, its base region is held at ground potential by the existing ground supply distribution system necessary for the conventional MTL logic circuits on the chip. This fixes the emitter potential of device b at approximately -0.8V. The emitter is in parallel with the emitters of other devices 8 in other circuits (not shown) of the same configuration contained on the chip. The current source resistor is contained off-chip and, therefore, dissipates its power off-chip, allowing higher circuit density to be achieved on-chip.

In the device structure under discussion, it should be noted that the collectors of devices 6, 6A, 7 and 8 are a common collector diffusion and, in fact, there is no need to provide a collector contact for the structure.

To eliminate parasitic PNP structures, either recessed-oxidation-isolations or subcollector reach-through diffusions are incorporated between all base diffusions.

Logical inputs to the current switch have lateral PNP pull-ups (devices 5 and 5A), although resistors could be substituted, which are device...