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Current Level Switching Driver Receiver

IP.com Disclosure Number: IPCOM000082463D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Swietek, DJ: AUTHOR

Abstract

In driving a high-capacitive line one of the limiting factors is the C dv/dt effect on the driving circuit. Therefore, it follows that if the Delta V on the line is minimized, the effect of the line capacitance will also be minimized. Switching current levels while holding the voltage relatively constant will accomplish this and still provide a communicating signal. The schematic depicts such a circuit.

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Current Level Switching Driver Receiver

In driving a high-capacitive line one of the limiting factors is the C dv/dt effect on the driving circuit. Therefore, it follows that if the Delta V on the line is minimized, the effect of the line capacitance will also be minimized. Switching current levels while holding the voltage relatively constant will accomplish this and still provide a communicating signal. The schematic depicts such a circuit.

The driver circuit operates as follows. When point A is up (V(BET1) + V(B1)), T1 and T2 are on, thereby creating the ability of sinking current from a load on the signal line. When point A is down, T1 and T2 are off, resulting in a high- impedance output.

The receiver circuit operates as a current sensing circuit having a sense transistor T3, which switches from a saturating to a nonsaturating mode of conduction.

Referring to the graph of I(E) vs. V(BE), T3 conducts along the V(BEO) curve when the driver is in a high -impedance state. The load line is effectively 1/(R3 + R4), resulting in a large base current through R4, and raising the voltage at point B. When the driver is on, T3 moves from the saturated to the normal forward conducting mode. It now operates on the V(BEX) curve along the load line of 1/(R3 + R4/ beta) and reduces the base current by a factor of approximately beta. This causes the voltage at point B to drop to a lower level.

It should be noted that from a practical point of view, due to T3 saturating, the l...