Bus switch having both p- and n-channel transistors for constant

Details Bus switch having both p- and n-channel transistors for constant Bus switch having both p- and n-channel transistors for constant

1998-01-09

2000-03-07

Tokar, Michael

Electronic digital logic circuitry

Interface

Current driving

326113, 326 57, 326 58, H03K 190175

Patent

active

060345535

ABSTRACT:
A bus switch uses both n-channel and p-channel transistors in parallel to connect two busses. The bus switch can be used on a network card to be plugged into a running network. During hot or live insertion of the network card into a live or hot bus, the network card and a bus switch are in a powered down state. Although n-channel transistors are normally off when the power is off, p-channel transistors can conduct. The hot bus could be disturbed when the bus switch is first connected since the p-channel transistor conducts when its gate is powered down to zero volts. A p-n junction from the p-channel transistor's drain to its substrate can become forward biased, drawing current from the hot bus. These problems are avoided by an isolation circuit that operates without power from a power supply. Instead, a high voltage from the hot bus is routed to the gate of the p-channel transistor, keeping the p-channel transistor turned off during hot insertion. The high voltage frog the hot bus is also routed to the substrate or N-well under the p-channel transistor, preventing the p-n junction from forward biasing. Thus a full CMOS bus switch can be used for live insertion, even when powered down.

REFERENCES:
patent: 5166957 (1992-11-01), Lenoir
patent: 5220211 (1993-06-01), Christopher et al.
patent: 5430396 (1995-07-01), Morano
patent: 5444397 (1995-08-01), Wong et al.
patent: 5455732 (1995-10-01), Davis
patent: 5467031 (1995-11-01), Ngyuyen et al.
patent: 5528190 (1996-06-01), Honnigford
patent: 5546017 (1996-08-01), Vitunic
patent: 5550699 (1996-08-01), Diaz
patent: 5583998 (1996-12-01), Bowman

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