Amplifiers – Combined with automatic amplifier disabling switch means
Reexamination Certificate
2001-08-24
2003-04-29
Tokar, Michael (Department: 2817)
Amplifiers
Combined with automatic amplifier disabling switch means
C330S057000, C330S086000, C330S144000
Reexamination Certificate
active
06556075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to amplifier systems that operate in forward and reverse modes.
2. Description of the Related Art
Gain programmable power amplifiers are essential in a variety of modern communication systems. In cable modem systems, for example, communication signals are transmitted “downstream” from a cable headend for reception by system subscribers and data signals are transmitted “upstream” from the subscribers. The downstream signals are generally transmitted in one frequency band (e.g., 45-800 MHz) and the upstream signals in a different frequency band (e.g., 5-43 MHz).
When transmitting data signals upstream in a “forward” transmit operational mode, an upstream amplifier preferably operates with minimal signal distortion, suppresses generation of transient signals, and provides an output impedance Z
out
that closely matches a cable impedance (e.g., 75 ohms). In order to avoid avoid degradation of a corresponding downstream amplifier, the upstream amplifier preferably continues to provide the output impedance Z
out
in a “reverse” power-down operational mode.
Conventional power amplifiers have typically attempted to meet these demanding requirements with amplifier structures (e.g., transformers and field-effect transistor (FET) switches) that impose significant cost and volume penalties and/or are not compatible with other integrated-circuit fabrication processes.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to amplifier systems and methods which closely approximate a constant output impedance and a constant quiescent output signal during forward and reverse modes of operation. These goals are realized with small, inexpensive components that are compatible with integrated-circuit fabrication processes.
In a system embodiment, a signal amplifier transitions from an enable state to a disable state in response to a signal-amplifier disable signal DS
sa
, a feedback path is coupled to the signal amplifier to reduce its impedance to a substantially lower enable state output impedance and a reverse amplifier transitions to an on state in response to a reverse-amplifier enable signal ES
ra
and is coupled to the feedback path.
The reverse amplifier thus interrupts the feedback path to thereby replace the enable state output impedance with the signal amplifier's higher impedance and forms, with the feedback portion, a disable state output impedance that approximates the enable state output impedance. A signal generator provides the signal-amplifier disable signal D
sa
and the reverse-amplifier enable signal ES
ra
with the reverse-amplifier enable signal ES
ra
initiated before the signal-amplifier disable signal DS
sa
and terminated after the signal-amplifier disable signal DS
sa
.
Another system embodiment includes an error-current canceler that comprises a current sensor which generates a sense signal in response to an error current I
err
that is generated by the signal amplifier as it transitions between its enable and disable states and further comprises a correction-current generator that responds to the sense signal by canceling the error current I
err
with a substantially equal and opposite correction current I
crctn
.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 4394542 (1983-07-01), Hara et al.
patent: 4608462 (1986-08-01), Blomley et al.
patent: 5182527 (1993-01-01), Nakanishi et al.
patent: 5442321 (1995-08-01), Bayruns et al.
patent: 5574992 (1996-11-01), Cygan et al.
patent: 5742204 (1998-04-01), Bell
patent: 5880631 (1999-03-01), Sahota
patent: 6040732 (2000-03-01), Brokaw
patent: 6313682 (2001-11-01), Muller et al.
“Maxim Upstream CATV Amplifier”, MAX3510 data sheet, Maxim Integrated Products, Sunnyvale, California.
“CATV Reverse Amp W/Step Attenuator”, Application Note, Anadigics, Inc., Warren, New Jersey.
Analog Devices Inc.
Koppel, Jacobs Patrick & Heybl
Nguyen Linh V
Tokar Michael
LandOfFree
Amplifier system and method that approximate constant... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Amplifier system and method that approximate constant..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Amplifier system and method that approximate constant... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3114001