Simultaneous bi-directional input/output (I/O) circuit

Electronic digital logic circuitry – Interface – Current driving

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327 27, 327 57, 327 83, H03K 190185

Patent

active

061278491

ABSTRACT:
A simultaneous bi-directional input/output (I/O) circuit (300) is disclosed. The I/O circuit (300) includes an output buffer (302) for driving a data bus line (306) high or low according to a data input signal (Din), and an input buffer (308) for sensing the voltage on the data bus line (306). The input buffer (308) drives a data output node (332) between logic levels by comparing the voltage on the data bus line (306) with a reference voltage (Vref1 or Vref2) that is determined by the data input signal (Din). To eliminate glitches at the data output node (332) caused by the reference voltages switching faster than the data bus line can be driven (306), a transition detector (314) is provided that generates a disable pulse when Din transitions between logic levels. The disable pulse prevents the input buffer (308) from driving the data output node (332) until after the data bus line (306) has been driven in response to the Din signal transition, thus eliminating glitches from being coupled to the data output node (332). Other embodiments delay the speed at which an old reference voltage is switched to a new reference voltage, so that the data bus line (306) has sufficient time to be driven, before the new reference voltage is applied to the input buffer (308), thus preventing the generation of glitches. Circuits for reducing current during both stand-by and active modes of operation are also disclosed.

REFERENCES:
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patent: 5438281 (1995-08-01), Takahashi et al.
patent: 5528168 (1996-06-01), Kleveland
patent: 5604450 (1997-02-01), Borkar et al.
patent: 5739701 (1998-04-01), Oshima
patent: 5872471 (1999-02-01), Ishibashi et al.
patent: 5936429 (1999-08-01), Tomita
Takahashi et al., "CMOS Gate Array with 600 Mb/s Simultaneous Bidirectional I/O Circuits," IEEE Journal of Solid State Circuits, Dec. 1995, pp. 1544-1546, vol. 30, No. 12.

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