Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
1999-04-27
2001-10-23
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S087000, C327S020000, C365S208000
Reexamination Certificate
active
06307405
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to integrated circuits. More particularly, it pertains to structures and methods for current sense amplifiers and current comparators with hysteresis.
BACKGROUND OF THE INVENTION
The use of voltage sense amplifiers with hysteresis for noise rejection is known. The simplest voltage sense amplifier is an operational amplifier in a positive feedback configuration. In the case of voltage hysteresis two different trip points (Tph and Tpl) are defined and circuits are designed such that when a high signal is to be recognized it must exhibit a voltage higher than Tph before it is recognized and declared a high signal. In a similar manner, before a low signal is recognized it must exhibit a low voltage lower than the second trip point Tpl. A simple illustration of this is provided in
FIGS. 1A
,
1
B, and
1
C.
In the quest for higher speed signaling it has recently been proposed to use current mode interconnections rather than voltage mode. The goal is to provide impedance matching on signal interconnection lines to reduce or avoid reflections and ringing on the lines. The technique proposed is matching termination of the signal line(s) to the signal receiver by using current mode interconnections and current mode sense amplifiers or current mode comparators. Signal interconnection and clock distribution lines with low controlled impedances are most amenable to current mode signaling. Metal lines separated from metal ground planes or metal power supply distribution planes (which are at AC ground) by oxide or other integrated circuit insulators will have low characteristic impedances of the order 50 or 75 ohms. To avoid reflections and ringing these need to be terminated in their characteristic impedance which requires sense amplifiers or receivers with low input impedances and implies small voltage swings on the lines. This is most easily accomplished by using current sense amplifiers which normally have a low input impedance. Rather than trying to sense the small voltage swings on the lines one can instead sense the current signal. Both single ended and differential configurations are possible. Current sense amplifiers have been described for use in SRAM's and in low impedance current-mode interconnections in CMOS integrated circuits with shielded interconnection lines. While this will reduce reflections and ringing it will not completely eliminate them. Also, this technique is still susceptible to noise transients.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, it is desirable to develop sense amplifiers or current comparators which are even less susceptible to induced noise, current reflections or ringing.
SUMMARY OF THE INVENTION
The above mentioned problems for high speed signaling as well as other problems are addressed by the present invention and will be understood by reading and studying the following specification. The present invention provides a current sense amplifier or current comparator with adjustable thresholds for the detection of valid signals coupled with the rejection of small noise current transients or reflections and ringing when using low impedance interconnections and/or current signaling. In particular, an illustrative embodiment of the present invention includes current sense amplifiers with hysteresis introduced as receivers for current mode signaling and/or clock distribution on low impedance integrated circuit interconnection lines. The introduction of hysteresis into the current sense amplifiers and/or receivers will allow them to discriminate against noise transients since the output will not change states unless the signal becomes more positive than a high trip point, Tph, or more negative than a low trip point, Tpl.
A first embodiment includes a current sense amplifier which has a first amplifier and a second amplifier. Each amplifier includes a first transistor of a first conductivity type and a second transistor of a second conductivity type, where the first and second transistors are coupled at a drain region. A signal input is coupled to a source region of the first transistor. A signal output node is coupled to the drain region of the first and the second transistor in the second amplifier. The signal output node is further coupled to a gate of a third transistor to introduce hysteresis for various values of an input current.
These and other method embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.
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Cloud Eugene H.
Forbes Leonard
Callahan Timothy P.
Englund Terry L.
Micro)n Technology, Inc.
Schwegman Lundberg Woessner & Kluth P.A.
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