Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
1999-08-25
2001-08-07
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S261000
Reexamination Certificate
active
06271725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to analog integrated circuits. More specifically, a low voltage bipolar transconductor circuit with extended dynamic range is disclosed.
2. Description of Related Art
A transconductor circuit is a circuit that converts a voltage input into a current output. The output of a transconductor circuit is dependent upon its gain, measured in units of conductance. The gain of a transconductor circuit is determined by the ratio of its output current I
O
to the input voltage V
IN
. The ratio I
O
/V
IN
is defined as the transconductance and is generally represented by g
m
.
Typically, a transconductor circuit has two voltage inputs V
1
and V
2
. In a normal mode of operation, the input voltages are changed differentially, independent of each other. In a common mode of operation, both input voltages change levels together. Transconductor circuits are often used as linear amplifiers. Measures of the performance of a transconductor circuit operating as a linear amplifier are its input voltage handling capability and its dynamic range.
U.S. Pat. No. 5,289,136, the entirety of which is incorporated by reference herein, discusses several examples of transconductance-based amplifiers such as emitter-coupled pair, series diode linearization, transistor ratio linearization, two differential pairs with ratios in parallel, and amplifiers using level shift techniques.
In analog signal processing, the typical frequency range of operation of linear circuits continues to increase with technological advances. Currently the typical frequency range of operation of linear circuits extends into several hundred Megahertz (MHz) and, in some cases, into the Gigahertz (GHz) range. The high frequency range of operation of linear circuits has been enabled by smaller geometries of integrated chips, necessitating in decreasing supply voltage operation.
For high speed considerations, the bipolar transistor is favored in linear circuits. However, the decrease in supply voltage is placing severe challenges in the design of such bipolar transistor linear circuits.
Accordingly, what is needed is a low supply voltage bipolar transconductor circuit having extended dynamic range which overcomes the supply voltage overhead problem. Preferably, the bipolar transconductor circuit can be operated at a low supply voltage and provide extended dynamic range without sacrificing signal handling capability and performance. Such a low supply voltage bipolar transconductor circuit having extended dynamic range would be particularly useful in high performance, high frequency analog circuits. Examples of such high performance, high frequency analog circuits include differential amplifiers, comparators, and filter transconductor elements.
SUMMARY OF THE INVENTION
A bipolar transconductor circuit is disclosed that is compatible with low supply voltage for operation and provides extended dynamic range. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
The transconductance circuit providing a differential current output signal generally comprises a first and a second differential pair of transistors having transistors area ratios of 1:r and r:1, respectively. Bases and collectors of the differential pair of transistors are coupled to a differential input signal and to a load, respectively. The transconductance circuit further comprises a first pair of diodes having positive nodes coupled to each other and to the load, and negative nodes coupled to emitters of the first differential pair of transistors, the first pair of diodes having a diode area ratio of r:1. The transconductance circuit further comprises a second pair of diodes having positive nodes coupled to each other and to the load, the second pair of diodes having negative nodes coupled to emitters of the second differential pair of transistors, the second pair of diodes having a diode area ratio of 1:r.
The transconductance circuit may further comprise at least one additional first pair of diodes and at least one additional second pair of diodes, the at least one additional first pair of diodes has an equal number of diodes as said at least one additional second pair of diodes. The at least one additional first pair of diodes are coupled in series with the first pair of diodes between the first pair of diodes and the first differential pair of transistors, each pair of the additional first pair of diodes having a diode area ratio of r:1. The at least one additional second pair of diodes are coupled in series with the second pair of diodes between the second pair of diodes and the second differential pair of transistors, each pair of the additional second pair of diodes having a diode area ratio of 1:r.
In another embodiment, the transconductance circuit providing a differential current output signal generally comprises a first and a second differential transistor having approximately equal transistors areas. Bases and collectors of the differential transistors are coupled to a differential input signal and to a load, respectively. The transconductance circuit further comprises a first pair of diodes having positive nodes coupled to each other and to the load, and negative nodes coupled to emitters of the differential transistors, the first pair of diodes having a diode area ratio of r
1
:r
2
. The transconductance circuit further comprises a second pair of diodes having positive nodes coupled to each other and to the load, and having negative nodes coupled to emitters of the differential transistors, the second pair of diodes having a diode area ratio of r
2
:r
1
.
The transconductance circuit may further comprise at least one additional first pair of diodes and at least one additional second pair of diodes. The at least one additional first pair of diodes are coupled in series with the first pair of diodes between the first pair of diodes and the differential transistors, each pair of the additional first pair of diodes having a diode area ratio of r
1
:r
2
. The at least one additional second pair of diodes are coupled in series with the second pair of diodes between the first pair of diodes and the differential transistors, each pair of the additional second pair of diodes having a diode area ratio of r
2
:r
1
. In one embodiment, r
1
is between approximately 3 and 8 and r
2
is between approximately 1 to 2.
These and other features and advantages of the present invention will be presented in more detail in the following detailed description and the accompanying figures which illustrate by way of example the principles of the invention.
REFERENCES:
patent: Re. 36861 (2000-09-01), Koyama et al.
patent: 4379268 (1983-04-01), Nagata
patent: 4707681 (1987-11-01), Eggenberger et al.
patent: 4748420 (1988-05-01), Metz
patent: 5006818 (1991-04-01), Koyama et al.
patent: 5081423 (1992-01-01), Koyama et al.
patent: 5289136 (1994-02-01), DeVeirman et al.
patent: 5343163 (1994-08-01), Linder et al.
Cideciyan, Roy D.; Dolivo, Francois; Hermann, Reto; Hirt, Walter, “A PRML System for Digital Magnetic Recording”, Jan. 1, 1992, IEEE Journal on Selected Areas in Communications.
N. Rao, V. Balan, R. Contreras, “A 3V 10-100 MHzContinuous-Time Seventh-Order 0.05° Equiripple Linear-Phase Filter”, 1999 International Solid-State Circuits Conference, San Francisco, CA., Feb. 15, 1999.
Balan Vishnu
Rao Narendra M. K.
LSI Logic Corporation
Nguyen Khanh Van
Pascal Robert
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