Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2002-02-25
2004-03-30
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
Reexamination Certificate
active
06714078
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to integrated circuits and, more particularly, to thermally-induced signal errors in integrated circuits.
2. Description of the Related Art
An exemplary integrated circuit differential amplifier
20
is shown in FIG.
1
. The amplifier
20
has a differential pair
22
of transistors
24
and
25
whose bases are coupled to a differential input port
26
by resistors
28
and
29
. Buffers
30
and
31
in the form of emitter-follower transistors couple collectors of the differential pair to an output port
32
and resistors
34
and
35
couple the collectors to a first voltage bias (e.g., ground). An exemplary bias generator in the form of a current source
36
(and its associated current source
37
) is coupled between the first bias source and a second bias source (e.g., V
ee
) and provides a stabilized current which is respectively mirrored by current mirrors
38
,
39
and
40
to the differential pair
22
and the buffers
30
and
31
.
In its operation, it is intended that the amplifier
20
of
FIG. 1
generates an output stream
43
of 50% duty-cycle pulses at the output port
32
in response to an input stream
42
of 50% duty-cycle pulses (for drawing clarity, the input pulse rise times are greatly exagerrated). As also indicated in
FIG. 1
, it is intended that the amplifier generates an output stream of pulses
45
at the output port whose duty cycle corresponds to that of an input stream
44
of pulses whose duty cycle differs from 50%.
It is often observed, however, that the fidelity of the output pulses degrades as the pulse-stream duty cycle departs from 50%. Examples of this observed signal degradation include:
a) the output duty cycle differs from the input duty cycle,
b) the output stream has an offset voltage and/or a time delay which is a function of duty cycle,
b) the output amplitude varies as a function of duty cycle; and
c) the output amplitude varies over time (i.e., droops or rises in waveforms that are often described as “thermal tails”).
This transfer-function degradation is highly undesirable as it generally produces processing errors in a variety of integrated circuits.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to reduction of differential-heating signal errors along differential signal paths of electronic circuits.
These goals are realized with a correction sensor that includes first and second transistors which are coupled to different sides of the differential signal path and a differential error amplifier that couples a differential correction signal to the differential signal path in differential response to a differential error signal generated by like terminals of the first and second transistors. In embodiments of the invention, the first and second transistors are directly connected to the different sides.
REFERENCES:
patent: 5424510 (1995-06-01), Gusinov et al.
patent: 5627495 (1997-05-01), Halbert et al.
patent: 6121798 (2000-09-01), McQuilkin
patent: 6246353 (2001-06-01), Elliott et al.
patent: 6288604 (2001-09-01), Shih et al.
patent: 6317001 (2001-11-01), Roth
Analog Devices Inc.
Koppel, Jacobs Patrick & Heybl
Mottola Steven J.
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