Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2002-06-13
2003-09-09
Nguyen, Patricia (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S253000
Reexamination Certificate
active
06617925
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data signaling devices, and more particularly, to low voltage differential signaling devices and methods that include gain compensation and bias control for stable operation over a wide range of common mode input voltages.
BACKGROUND OF THE INVENTION
Low voltage differential signaling (LVDS) applications have become common, particularly with the popularity of CMOS technology. Certain industry standards for LVDS are specified by ANSI/TIA/EIA-644 and IEEE 1596.4.
An example LVDS application is shown in FIG.
1
. As shown in
FIG. 1
, two circuits
102
and
104
(on the same circuit board or integrated chip, or on separate such components) communicate with each other over a pair of conductors
110
using LVDS signaling. In such an example, an LVDS driver
106
sends a differential signal to be received by LVDS receiver
108
by driving opposite polarity (i.e. complementary) signals on each conductor, both polarity signals having the same common-mode voltage. LVDS requires the combined differential voltage on conductors
110
to be no more than 600 mV. Although the common-mode voltage may vary due to noise and temperature conditions, for example, preferably the common-mode voltage is about 1.2V. However, LVDS requires receivers to be able to understand signals that range between 0V and 2.4V.
As illustrated in
FIG. 2
, signals
202
and
204
that are received by an LVDS receiver may technically be in compliance with LVDS. (It should be understood that the signal on only one conductor is shown and that there will actually be a pair of complementary signals having opposite polarity on the conductors at the same common mode voltage). Signal
202
has a high common mode voltage Vcm(high) such that it ranges at or just below the upper LVDS range of 2.4V, while signal
204
has a low common mode voltage Vcm(low) such that it ranges at or just above the lower LVDS range of 0V. Although both signals
202
,
204
are in technical compliance with LVDS standards, they pose problems for conventional LVDS receivers. For example, if receiver
108
is biased for signals having a common-mode voltage of 1.2V, it may operate poorly or not at all when the signals are close to the extreme low and high values of 0V and 2.4V, thereby preventing data signals between circuits
102
and
104
from being properly communicated.
SUMMARY OF THE INVENTION
The present invention relates to differential data signaling devices and methods. In accordance with one aspect of the invention, a differential signaling receiver includes a gain compensation and control circuit having a low common mode compensation circuit and a high common mode compensation circuit. A control circuit is coupled to both compensation circuits and senses the operation of one to control the operation of the other. The operation of the compensation circuits ensures that differential signals having a wide range of common mode input voltages are accurately detected by the receiver. The control circuit serves to keep the combined operation of the compensation circuits stable over the wide range of common mode input voltages.
REFERENCES:
patent: 5684429 (1997-11-01), Sanwo et al.
patent: 5939904 (1999-08-01), Fetterman et al.
patent: 5977796 (1999-11-01), Gabara
patent: 6028467 (2000-02-01), Burrows et al.
patent: 6194949 (2001-02-01), Hogeboom
patent: 6201405 (2001-03-01), Hedberg
patent: 199 22 354 (2000-05-01), None
patent: 0 788 059 (1997-08-01), None
patent: 2000031810 (2000-01-01), None
patent: 2000134082 (2000-05-01), None
Nguyen Patricia
Nurlogic Design, Inc.
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