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Current-Limited Inverter

IP.com Disclosure Number: IPCOM000047839D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Banker, DC: AUTHOR [+3]

Abstract

The current-limited inverter (CLI) uses a pinch resistor to supply base current to a logic inverter. The pinch resistor current source enables the circuit to operate at very low supply voltages. If the voltage across the pinch resistor is small, the resistance of the pinch resistor is essentially RDB. RDB and forward beta are well correlated, such that an increase in RDB implies a proportionate increase in beta. Consequently, in the circuit of Fig. 2, the current I remains fairly constant despite process variations in beta. Additionally, if the collector of T4 in Fig. 2 were left open, T4 would saturate and very little power would be dissipated. The CLI circuit (Fig. 1) comprises an emitter-coupled pair in series with a pinch resistor current source.

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Current-Limited Inverter

The current-limited inverter (CLI) uses a pinch resistor to supply base current to a logic inverter. The pinch resistor current source enables the circuit to operate at very low supply voltages.

If the voltage across the pinch resistor is small, the resistance of the pinch resistor is essentially RDB. RDB and forward beta are well correlated, such that an increase in RDB implies a proportionate increase in beta. Consequently, in the circuit of Fig. 2, the current I remains fairly constant despite process variations in beta. Additionally, if the collector of T4 in Fig. 2 were left open, T4 would saturate and very little power would be dissipated. The CLI circuit (Fig. 1) comprises an emitter-coupled pair in series with a pinch resistor current source. A clamped resistor from supply to collectors provides voltage level changes sensitive to the on/off state of T1 and T2. When inputs A and B are low, T1 and T2 are both off, and device T3 is saturated. The circuit dissipates negligible power in this state. If one or both of the inputs rise, one or both of the input devices turn on, and the output falls to about 0.6 V. In this transition, the saturated current source behaves as a speed-up capacitor, enhancing performance significantly. When both inputs go low again, the output rises to about the power supply level. Since the supply voltage can be quite low, the resistor R1 can be small, giving fast rising transitions at affordable power.

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