Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2000-11-22
2002-08-27
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S558000, C327S379000
Reexamination Certificate
active
06441682
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the field of active polyphase filter design. More particularly, the invention relates to the use of transconductors to cross-couple active polyphase filters sections.
BACKGROUND OF THE INVENTION
Polyphase filters receive an N-phase (or polyphase) input signal and create an N-phase output signal. A quadrature filter is a four-phase polyphase filter. In a quadrature filter, the input will consist of four signal voltages of mutually equal value. These four input signals jointly constituting a signal vector group with the individual signal vectors succeeding one another in a given direction of rotation through phase angles of 90 degrees. Dependent on direction of rotation, counter-clockwise or clockwise, the frequency of the polyphase signal is positive or negative. The I degree and 180 degree signal vectors are designated the +1 and −I signals. The 90 degree and 270 degree signal vectors are designated the +jQ and −jQ signals. Such a polyphase filter is known from the article “Asymmetric Polyphase Networks” by M. J. Gingell, published in “Electrical Communication”, Vol. 48, no. 1 and 2, 1973, pp. 21-25.
Passive LC filters are limited by the difficulty of incorporating inductors into integrated circuits. To replace inductors and reduce sensitivity to component variations, active-RC filters were introduced. Operational amplifiers and, in some designs, gyrators are the reactances in an active-RC design. Active-RC filter circuits are easier to design and manufacture than passive filters. Feedback loops between the inputs and outputs of the active-RC reactances replace the need for inductive elements and reduce sensitivity to component variation.
The conversion of passive-LC filters designs to active-RC filter designs, termed “filter design,” is the subject of many publications. Filter design begins with the choice of a passive filter. The most common types of passive filters are the gaussian, Butterworth, Bessel, and Chebyshev filters. The type of passive filter is chosen based upon its characteristics, such as ripple, stopband rejection, pole quality factor, noise figure, and sensitivity. The order of the filter, an indication of the number of poles in the filter, is also chosen. The choice of filter type and order is based on the constraints of the intended manufacturing process and end-use. After a filter type and order are chosen, nodal transfer functions (generally represented in Laplace notation) for the filter are derived. e nodal transfer functions allow a signal flow graph of the passive filter to be mapped. The noaltransfer functions of the passive filter are then replaced with active elements, resistors, and capacitors. The resulting active-RC filter network has a filter transfer function equivalent to the passive filter.
Three books that demonstrate filter design techniques are: (i) Handbook of Filter Synthesis, by Anatol I. Zverev, published 1967 by John Wiley & Sons; (ii) Electronic Filter Design Handbook, by Arthur B. Williams, published 1995 by McGraw Hill; and (iii) Analog MOS Integrated Circuits for Signal Processing, by Roubik Gregorian and Gabor C. Temes, published 1986 by John Wiley & Sons. In these books, schematics and tables of figures detail XT the configuration and component values for a broad range of filter types and orders. A detailed example of filter design can also be found in the following U.S. Patents: (i) “Symmetrical Polyphase Networks Utilizing Constant Reactances” by Michael John Gingell, number 3,618,133, issued 1971; and (ii) “Asymmetric Polyphase Filter” by Johannes O. Voorman, number 4,914,408, issued 1990 (hereafter “Voorman Patent”). Computer programs for filter design are also available.
An example of filter design is illustrated in
FIGS. 1A and 1B
.
FIG. 1A
shows a low-pass third-order passive LC filter
1
with four nodes, N
1
, N
2
, N
3
, and N
4
, numbered sequentially clockwise from the top left. The input voltage Vin is applied across N
1
and N
4
. The output voltage Vout is measured across N
3
and N
4
. A first resistor RP
1
is connected between N
1
and N
2
. A first capacitor CP
1
is connected between N
2
and N
4
. An inductor LP
1
is connected between N
2
and N
3
. A second capacitor CP
2
and a second resistor RP
2
are connected in parallel across N
3
and N
4
.
FIG. 1B
shows a low-pass third-order active-RC filter block (hereafter “FB”) that approximates the transfer function of the low-pass third-order passive LC filter shown in FIG.
1
A. FB includes: two input terminals IA and IB; two output terminals OA and OB; three reactances X
1
, X
2
, and X
3
; and fourteen matched resistors R. Each reactance is an active balanced integrating circuit than includes: one balanced differential amplifier
2
, a reactance input pair
3
; a reactance output pair
4
; and a matched capacitor pair C
1
, C
2
, and C
3
. In each matched capacitor pair: one capacitor is shunted between the first input of a reactance input pair
3
and the first output of the reactance output pair
4
; and the other capacitor is shunted between the second input of the reactance input pair
3
and the second output of the reactance output pair
4
.
The internal nodes of FB can be identified by their associated terminal
5
, as set forth in below Table I below.
TABLE 1
FB Nodes Identified by Terminal Number
Reactance
First/Second
Input/Output
Terminal
X1
second
input
T1A
X1
first
input
T1B
X1
second
output
T1C
X1
first
output
T1D
X2
second
output
T2A
X2
first
output
T2B
X2
first
input
T2C
X2
second
input
T2D
X3
second
input
T3A
X3
first
input
T3B
X3
second
output
T3C
X3
first
output
T3D
Note also that output terminal OA is attached to terminal T
3
C and that output OB is attached to terminal T
3
D. The Table II netlist below indicates the location of the fourteen matched resistors R. In table II, one matched resistor R is connected between the first node and the second node.
TABLE II
Resistors Connected Within FB
First Node
Second Node
IA
T1A
IB
T1B
T1A
T2A
T1B
T2B
T1C
T2C
T1D
T2D
T2A
T3A
T2B
T3B
T2C
T3C
T2D
T3D
T1A
T1C
T1B
T1D
T3A
T3C
T3B
T3D
While resistors R are shunted across X
1
and X
3
, no resistors R are shunted across X
2
.
FIG. 1C
shows a block diagram of FB. The block diagram has two inputs IA and IB. The block diagram has two outputs OA and OB. The block diagram also has three sets of four-lead terminals T
1
-T
3
for a total of twelve terminals. The first set is labeled T
1
and is composed of four terminals T
1
A, T
1
B, T
1
C, and T
1
D. The second set is labeled T
2
and is composed of four terminals T
2
A, T
2
B, T
2
C, and T
2
D. The third set is labeled T
3
and is composed of four terminals T
3
A, T
3
B, T
3
C, and T
3
D. Figure IC also demonstrates how FB can be attached to a 2-phase input +Iin and −Iin, by input terminals IA and IB respectively, to generate a 2-phase output +Iout and −Iout, through output terminals OA and OB respectively.
A second example of filter design is shown in
FIGS. 1D and 1E
.
FIG. 1D
shows a low-pass sixth-order passive LC filter
6
with six nodes, NZ
1
, NZ
2
, NZ
3
, NZ
4
, NZ
5
, and NZ
6
, numbered sequentially clockwise from the top left. The input voltage Vzin is applied across NZ
1
and NZ
6
. The output voltage Vzout is measured across NZ
5
and NZ
6
. A first resistor RPZ
1
is connected between NZ
1
and NZ
2
. A first capacitor CPZ
1
is connected between NZ
2
and NZ
6
. A first inductor LPZ
1
is connected between NZ
2
and NZ
3
. A second capacitor CPZ
2
is connected between NZ
3
and NZ
6
. A second inductor LPZ
2
is connected between NZ
3
and NZ
4
. A third capacitor CPZ
3
is connected between NZ
4
and NZ
6
. A third inductor LPZ
3
is connected between NZ
4
and NZ
5
. A second resistor RPZ
2
is connected between NZ
5
and NZ
6
.
FIG. 1E
shows a low-pass sixth-order active-RC filter block (hereafter “FBZ”) that approximates the transfer function of the low-pass sixth-order passive LC filter shown in FIG.
1
D. FBZ includes: two input terminals IZA and IZB; two output terminals OZA
Laber Carlos
Luff Gwilym
Vinn Charles
Callahan Timothy P.
Haverstock & Owens LLP
Micro Linear Corporation
Nguyen Hai L.
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