Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synchronizing
Reexamination Certificate
2001-03-30
2003-01-28
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synchronizing
C327S144000, C327S295000, C327S551000
Reexamination Certificate
active
06512402
ABSTRACT:
COPYRIGHT NOTICE
Contained herein is material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction of the patent disclosure by any person as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all rights to the copyright whatsoever.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to the field of electronics. In particular, the present invention is related to a method and apparatus for shifting the frequency spectrum of noise signals in electronic circuits.
2. Description of the Related Art
The existence of noise in electronic circuits may cause the circuits to malfunction. This is especially true in electronic communication devices wherein the existence of noise has the potential to drown out or distort the desired signals. The effects of noise in electronic circuits is illustrated with reference to
FIGS. 1-3
.
FIG. 1
illustrates a block diagram of a conventional communication system
10
. Communication system
10
includes a transmitter
12
, a receiver
14
and a communication channel
16
. Communication channel
16
may be either a wired or wireless communication channel.
FIG. 2
illustrates a sequence of waveforms, for example, as may be transmitted over communication system
10
. Input signal
20
is a binary signal and comprises a sequence of binary values received by transmitter
12
of FIG.
1
. Transmitter
12
converts the binary input signal into a bipolar signal
22
, having a positive and a negative component. The bipolar signal
22
is transmitted to receiver
14
via communication channel
16
. In one embodiment, transmitter
12
may modulate bipolar signal
22
onto a carrier wave prior to transmitting the signal to receiver
14
.
As bipolar signal
22
propagates through communication channel
16
, the signal may become deformed and attenuated as illustrated by waveform
24
in FIG.
2
. Receiver
14
receives attenuated signal
24
and transmits it to equalizer (wave shaper)
18
. Equalizer
18
amplifies and processes signal
24
, producing a reconstructed signal
26
, which is more or less a replica of bipolar signal
22
.
At the input of equalizer
18
both the desired input signal
20
, and unwanted noise signals are present and, hence, amplified by the equalizer. If the noise signals are of significant amplitude, i.e., if the noise signals have an amplitude larger than the desired signal and have a substantially similar frequency as the desired input signal
20
, the noise signals may distort the desired signal. In this case, the equalizer would be unable to reconstruct the desired signal.
In order to propagate a desired input signal
20
through e.g., a communication system
10
, switching circuits driven by clock signals often are employed in the receiver
14
and equalizer
18
. As such, the undesired signals, for example, noise signals generated by the clock signals and the associated switching circuitry are at frequencies that are multiples of the clock signal frequency. The noise signal frequencies normally fall within the bandwidth of amplifiers in the communication system
10
, and subsequently both the desired input signal
20
and the noise signals are amplified. Moreover, since the amplitude of the noise signals, of a particular frequency, generated by different switching circuits in the system are additive, noise signals from the various switching circuits may be superimposed on each other to form noise signals of greater amplitude, exaggerating the problem.
FIG. 3
illustrates a waveform showing the gain versus frequency curve of various signals at the input of equalizer
18
. As
FIG. 3
illustrates, the desired input signal
20
has a frequency of 100 MHz, a clock signal has a frequency of 25 MHz, harmonics of the clock signal have frequencies of 50 MHz, 100 MHz, 150 MHz etc. All the frequencies illustrated are present at the input of the equalizer
18
. Hence, as the desired 100 MHz input signal
20
is amplified by the equalizer, so too are the undesired noise signals.
Conventional noise reduction methods and systems attempt to increase output signal quality by reducing the induced noise signals via the use of filter circuits. Using filter circuits to eliminate noise signals is not very effective, as noise signals induced by clock transitions, and with frequencies substantially similar to the desired signal frequency cannot be easily filtered out. What is needed, therefore, is a method and apparatus to reduce noise signals in electronic devices by shifting the frequency spectrum of noise signals to frequencies outside the bandwidth of the amplifiers, or to frequencies that are outside the operating frequency of the electronic system.
REFERENCES:
patent: 4348640 (1982-09-01), Clendening
patent: 5764998 (1998-06-01), Deshpande
patent: 6020773 (2000-02-01), Kan et al.
patent: 6046607 (2000-04-01), Kohdaka
patent: 6275087 (2001-08-01), Dehghan
patent: 6285768 (2001-09-01), Ikeda
patent: 571 209 (1993-11-01), None
patent: 08330917 (1996-12-01), None
patent: 11007349 (1999-01-01), None
patent: 2001084053 (1999-09-01), None
Ultra320 White Paper, www.maxtor.com/Quantum/src/whitepapers/wp_ultra320.htm, pp. 2 through 5, Aug. 31, 2001.
Ravid Shmuel
Rettig Dany
Blakely , Sokoloff, Taylor & Zafman LLP
Callahan Timothy P.
Intel Corporation
Luu An T.
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