Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
1999-09-24
2003-09-09
Trost, William (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S077000, C327S552000
Reexamination Certificate
active
06618579
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrical filter circuit, and in particular, an electrical filter circuit which includes a bypass mode for bypassing a filtering portion of the circuit.
DESCRIPTION OF THE RELATED ART
Filter circuits are well known in the art and are used in various applications. Filters are often used widely in telecommunications applications. For instance, wireless (e.g. cellular) communications equipment include various filters for performing the to different functions of the equipment. An example may include a reconstruction filter which follows a digital to analog (D/A) conversion device in either of the transmit or receive channels of the wireless equipment.
One well known filter circuit is the Salen and Key filter. The Salen and Key filter is an active filter which includes two basic elements: a filtering element and a amplification element.
FIG. 1
shows a conventional second order low pass Salen and Key filter
10
. The filter
10
includes an amplifier
20
for providing amplification, and an R-C network including two capacitors
30
,
40
and two resistors
50
,
55
for providing filtering. The filter
10
also includes resistors
60
and
65
which set the gain of the amplifier
20
. The filter
10
includes an input terminal
12
and an output terminal
14
. Signals which are presented at the input terminal
12
of the filter
10
are attenuated (and appear as such as output terminal
14
) according to the passband of the low pass filter formed by capacitors
30
,
40
and resistors
50
,
55
. Signals which are within the passband are amplified by amplifier
20
with a particular gain set by resistors
60
and
65
.
Active filters such as Salen and Key filter
10
described above may be used for a variety of different reasons, including: (1) the filter function is required to multiple order, (2) large signal swing requirements, (3) linearity requirements, and (4) output drive requirements. It should be noted that the component values of the capacitors (e.g. capacitors
30
,
40
) of the filter
10
can be adjusted to more accurately tune the passband of the filter. This is typically accomplished by making one of the capacitors
30
,
40
a variable capacitor, tuning that capacitor and a resistor (e.g. resistor
50
or
55
) to a known time reference, and then tuning the other elements in accordance therewith.
Other examples of conventional active filter structures are the second order Rausch filter and the “leaky” integrator filter shown in
FIGS. 2 and 3
, respectively. The Rausch filter
100
includes an amplifier
120
for providing amplification, and an R-C network including two capacitors
130
,
140
and three resistors
150
,
155
,
160
for providing filtering. The “leaky” integrator filter
200
shown in
FIG. 3
includes an amplifier
220
and an R-C network including one capacitor
230
and two resistors
250
,
260
for providing filtering. It will be noted that the filters shown in
FIGS. 2 and 3
(e.g. Rausch and “leaky” integrator) have similar construction to the Salen and Key filter (shown in FIG.
1
), but are slightly different as to the placement of the resistors and capacitors. However, all three conventional filters described above include capacitors which contribute to the filtering functions of the circuits.
Another conventional filter circuit
600
is shown in FIG.
4
.
FIG. 4
shows a full-differential third order Rausch filter. The filter
600
includes an amplifier
620
for amplification, and an R-C network including capacitors
630
,
635
,
640
, and
645
and resistors
650
-
657
for providing filtering. The filter
600
differs from the other conventional filter circuits
10
,
100
, and
200
described above in that it includes balanced input
610
,
611
and output
612
,
613
terminals rather than unbalanced input and output terminals, and the amplifier
620
includes two output terminals, instead of just one.
In a conventional filter circuit applications, such as those described above, a mode may exist where the filtering function of the filter circuit is not desired, but the loading conditions on the output remain unchanged. Previous solutions to this problem required at least two buffer circuits, one with filtering elements and one without filtering elements, to accommodate both modes of operation. The requirement of two buffers requires additional area on either the silicon die or the circuit board on which the filter circuit is disposed.
Thus, there is currently a need for a combined filter and buffer circuit which includes a filter bypass mode.
SUMMARY OF THE INVENTION
The present invention is method and apparatus for providing an electrical circuit which includes a filter bypass mode. The method includes the steps of: providing at least one switched filtering element in a filtering circuit, and switching the filtering element out of the filter circuit in order to bypass the filter circuit.
The above and other advantages and features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention which is provided in connection with the accompanying drawings.
REFERENCES:
patent: 4453258 (1984-06-01), Richardson
patent: 5027814 (1991-07-01), Carroll et al.
patent: 5063782 (1991-11-01), Kellett
patent: 5241283 (1993-08-01), Sutterlin
patent: 5450622 (1995-09-01), Vandegraaf
patent: 5523719 (1996-06-01), Longo et al.
patent: 5654550 (1997-08-01), Nomura et al.
patent: 5914633 (1999-06-01), Comino et al.
patent: 6253612 (2001-07-01), Lemkin et al.
Lesher Mark K.
Risk Valerie J.
Smith Malcolm H.
Chase Manhattan Bank
Sobutka Philip J.
Trost William
LandOfFree
Tunable filter with bypass 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 filter with bypass, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tunable filter with bypass will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3052400