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High Simultaneous Switching TTL Drive

IP.com Disclosure Number: IPCOM000041303D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Gaudenzi, GJ: AUTHOR [+3]

Abstract

The illustrated circuit is an off-chip driver having TTL (transistor-transistor logic) output levels (.6 V to 2.4 V). The driver is powered from a 1.7 V and 3.4 V power supply. The WI/Wt of the output load current is controlled (<5 ma/ns) to enable a sizeable number of these drivers to be switched simultaneously. The circuit utilizes active feedback to limit output WI/Wt. Note that resistor RP senses the output voltage and biases the active feedback circuit. Consider the case when input A is at a logical 0 level. The output A is at a logical 1 level, and transistor T4 is on, supplying current to T8 and TFB. When input A goes to a logical 1 level, T2 and T3 turn on, which results in T6 turning off. Most of the emitter current of T2 will flow into the collectors of T8 and TFB.

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High Simultaneous Switching TTL Drive

The illustrated circuit is an off-chip driver having TTL (transistor-transistor logic) output levels (.6 V to 2.4 V). The driver is powered from a 1.7 V and 3.4 V power supply. The WI/Wt of the output load current is controlled (<5 ma/ns) to enable a sizeable number of these drivers to be switched simultaneously. The circuit utilizes active feedback to limit output WI/Wt. Note that resistor RP senses the output voltage and biases the active feedback circuit. Consider the case when input A is at a logical 0 level. The output A is at a logical 1 level, and transistor T4 is on, supplying current to T8 and TFB. When input A goes to a logical 1 level, T2 and T3 turn on, which results in T6 turning off. Most of the emitter current of T2 will flow into the collectors of T8 and TFB. As T6 turns off, T4 will turn off, which results in T8 and TFB turning off. Since TFB operates in the saturated mode, T8 and TFB will turn off slowly. As T8 and TFB slowly turn off, the base current of T7 will increase at a controlled rate resulting in the emitter and collector current of T7 to also increasing at a controlled rate (WI/Wt < 5 ma/ns). By adjusting RSFB lower, the level of saturation of TFB and consequently the Toff delay of TFB is increased, resulting in lower values of WI/Wt and higher driver simultaneous switching.

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