Amplifiers – With semiconductor amplifying device
Reexamination Certificate
2003-01-24
2004-07-20
Nguyen, Patricia (Department: 2817)
Amplifiers
With semiconductor amplifying device
C330S258000, C330S306000
Reexamination Certificate
active
06765441
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to differential amplifiers. More specifically, a differential amplifier that has a wide range of operating frequencies is disclosed.
BACKGROUND OF THE INVENTION
Differential amplifiers are often used in applications that require low noise amplification.
FIG. 1
is a circuit diagram of a typical differential amplifier. Transistors
100
and
102
are connected to load resistors
104
and
106
, respectively. The load resistors are connected to a voltage source, Vcc, at
116
. Two input signals are applied to the gate terminals
110
and
112
of transistors
100
and
102
. The output is taken between the drain terminals
118
and
120
of the transistors. Ideally, the output represents the difference between the two inputs.
Transistor
108
is a current source for transistors
100
and
102
. The sources of transistors
100
and
102
are connected together with the drain of transistor
108
, at node
114
. Because the circuit is symmetrical, for AC input signals that are opposite of each other, the resulting signals at the sources of the transistors cancel each other at node
114
. Thus, node
114
appears as AC ground for differential inputs.
The amplifier sometimes receives common mode inputs at its input interfaces. Common mode input signals are signals that are substantially the same. They are often caused by noise and are undesirable. The common mode signals are rejected when the common mode gain is small. To achieve small common mode gain, the impedance between node
114
and ground should be relatively high. In practice, however, the common mode gain is increased at higher operating frequencies due to parasitic capacitance, and the amplifier's operating frequency range is reduced.
Ideally, the headroom consumed by transistor
108
should be as low as possible, thereby allowing greater output range for transistors
100
and
102
. For a given current, a larger transistor can be used to achieve lower headroom. However, a larger transistor generally has larger parasitic capacitance associated with it, and would increase the common mode gain at higher frequencies and reduce the amplifier's operating range. It would be useful to have a differential amplifier design that has low common mode gain at high frequencies, large operating frequency range and better headroom for the output transistors.
REFERENCES:
patent: 4468628 (1984-08-01), Gross
patent: 5420524 (1995-05-01), Webster
patent: 5422529 (1995-06-01), Lee
patent: 6211718 (2001-04-01), Souetinov
Hegazi,, Emad, et al., “A Filtering Technique to Lower LC Oscillator Phase Noise”, IEEE Journal of Solid-State Circuits, vol. 36, No. 12, Dec. 2001.
Atheros Communications Inc.
Nguyen Patricia
Van Pelt & Yi LLP
LandOfFree
Differential amplifier does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Differential amplifier, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Differential amplifier will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3211383