Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
1999-09-22
2002-08-27
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S174000, C333S175000
Reexamination Certificate
active
06441701
ABSTRACT:
TECHNICAL FIELD
This invention relates in general to electrical circuits, and more specifically to a tunable filter.
BACKGROUND
One or more filters, usually in the form of pass-band filters provide the front-end selectivity for a radio receiver. Such filters either are designed to have fixed bandwidths or they may have tunable bandwidths. Tunable bandwidth filters are usually used in wideband receivers where the operational frequency range is large. Most tunable filters use varactors as the tuning element. Each resonator element in the filter includes one or more varactors that in response to a control voltage provides the tuning mechanism for the filter. By varying the control voltage, the filter may be tuned to provide a narrow bandwidth for a desired frequency of operation.
In
FIG. 1
there is shown a prior art receiver
100
. An antenna
102
is used to receive radio frequency (RF) signals which are sent to a first filter also known as a pre-selector
104
. The main function of filter
104
is to limit the bandwidth of the spectrum reaching the radio frequency amplifier
106
in order to minimize IM distortion and to attenuate the receiver spurious responses (e.g., image, ½ intermediate frequency (IF), etc.). The typical selectivity for filter
104
is in the range of 35-40 dB. As such, if a high selectivity receiver is required, a second filter stage
108
is used to provide for another 35-40 dB of selectivity.
As is done in conventional receivers, the filtered signal is then multiplied by mixer
110
with a local oscillator (LO) signal
112
. The result of this multiplication process is a pair of output intermediate frequencies (IFs)
114
that are the sum and difference of the signal and LO frequencies. One of these IFs
114
is selected as the desired IF which is then band-pass filtered and amplified (circuitry not shown). The amplified signal is then sent through a second mixer or detector which translates the IF signal to baseband (audio) where it is further amplified and filtered prior to being presented to the user.
The main problem with the receiver
100
is that in order to achieve high selectivity, for example, over 90 dB at the image frequency, two or more filter stages
104
and
108
are needed. The use of multiple filter sections
104
and
108
adds to the overall cost of the receiver, since more components, shields, etc. are required. The cost of adding such extra filter sections is even higher in tunable filters given that tunable filters need to use expensive components such as varactors. Therefore, there exists a need for a tunable filter that can provide high selectivity while minimizing the cost of the filter.
REFERENCES:
patent: 1632814 (1927-06-01), Zinn
patent: 1647634 (1927-11-01), Johnson
patent: 3533020 (1970-10-01), Hecht
patent: 3569846 (1971-03-01), Matsuura
patent: 5148133 (1992-09-01), Zennamo, Jr. et al.
patent: 5576756 (1996-11-01), Baty et al.
Williams, Electronic Filter Design Handbook, 1981, McGraw-Hill, Inc., p. 5-19.
Bettendorf Justin P.
Garrett Scott M.
Jones Stephen E.
Motorola Inc.
LandOfFree
Tunable bridged-T filter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tunable bridged-T filter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tunable bridged-T filter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2909315