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Level Shifting Circuit

IP.com Disclosure Number: IPCOM000082471D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Daniels, RJ: AUTHOR [+2]

Abstract

Current mode logic gate 10 drives a current-source transistor 1 which draws current through transistors 3 and 5 and resistor 9, so that the voltage drop across resistor 9 is slightly less than the reference voltage VREF1. The collector current (IC) (1) drawn by current-source transistor 1 flows alternately through transistor 3 or transistor 5, depending upon whether logic input voltage A is above or below the reference voltage VREF2, respectively. Since VREF2 is only approximately 0.2 volt less than +V, output node 11 cannot drive transistor-transistor logic (T/2/L).

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Level Shifting Circuit

Current mode logic gate 10 drives a current-source transistor 1 which draws current through transistors 3 and 5 and resistor 9, so that the voltage drop across resistor 9 is slightly less than the reference voltage VREF1. The collector current (IC) (1) drawn by current-source transistor 1 flows alternately through transistor 3 or transistor 5, depending upon whether logic input voltage A is above or below the reference voltage VREF2, respectively. Since VREF2 is only approximately
0.2 volt less than +V, output node 11 cannot drive transistor-transistor logic (T/2/L).

Level shifting circuit 20 converts the current mode low-voltage excursion at output node 11 into a high speed, large voltage swing at output node 29 using a relatively slow-speed PNP laterally diffused device. These PNP devices are inherently orders of magnitude slower than their NPN counterparts, when diffused into the same integrated circuit chip. In this circuit, transistor 21 is never switched on or off, but rather is switched between a first collector current of, for example, 0.5 IC (23) and 1.5 IC (23) as the conductivity of transistor 5 changes with input signal A.

Voltage reference circuit 40 generates reference voltage VREF3 from reference voltage VREF1. Resistor 27 is chosen with respect to resistor 9 so that IC (1) equals IC (23). Resistor 49 is chosen with respect to resistor 9 so that IC (43) equals 1.5 IC (1) and 1.5 (23).

Transistor 43 operates as a current source driving transistor 41 so that emitter current (IE) (41) is approximately equal to IC (43), thereby fixing reference voltage VREF3. If re...