Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2000-06-15
2002-07-02
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S337000
Reexamination Certificate
active
06414541
ABSTRACT:
TECHNICAL FIELD
The invention concerns switched capacitor technology, specifically variable value switched capacitor circuits and switched capacitor filters, such as finite impulse response filters (FIR-filter), with variable value switched capacitor circuits.
BACKGROUND
Switched capacitor circuits are used for their suitability to be placed on a single semiconductor chip thereby replacing filters that have been conventionally constructed using discrete resistors, capacitors and inductors. In switched capacitor circuits, resistors and inductors are replaced by switches and capacitors.
Finite impulse response filters (FIR-filters) can be expressed as a series, for example such as
y
(
k
)
=
∑
n
=
0
k
g
(
n
)
*
x
(
n
)
,
where g(n) is the n:th weight factor/coefficient for the n:th input value x(n). Expanded it will end up to be y(k)=g(0)*x(0)+g(1)*x(1)+g(2)*x(2)+. . . +g(k−1)*x(k−1)+g(k)*x(k). The series needs k+1, possibly different, weights/coefficients if it has k terms and an initial value. An implementation of such an equation would not be practical. If a simple and flexible solution to this is desired then an implementation of the recursive equation y(k)=y(k−1)+g(k)*x(k) is preferably made. However, an implementation according to the recursive equation requires dynamically adjustable coefficients. In an implementation utilizing switched capacitor technology the value of the coefficient can be varied by, for example, dividing the sampling capacitor into a suitable number of equal sized part-capacitors, for example 256 part-capacitors. The number of part-capacitors used will depend on the desired resolution of the coefficient, a 12 bit resolution coefficient, for example, needs 4096 capacitors. During each sampling all of the sampling capacitors are charged to the input signal value. Thereafter, the input is disconnected and a number of the capacitors representing the desired filter coefficient, are connected to an output circuit, in this case an integrator. An example of such a circuit is described in the U.S. Pat. No. 5,220,286. This method of obtaining a variable coefficient circuit can suitably be named the capacitance division method. A disadvantage can be considered to be the large number of capacitances and corresponding switches that are necessary if a high resolution is desired.
SUMMARY
An object of the invention is to define a variable value switched capacitor circuit requiring a drastically reduced number of capacitors and switches in relation to a circuit according to the capacitance division method.
Another object of the invention is to define a method of controlling a switched capacitor circuit to thereby obtain a variable value switched capacitor with a drastically reduced number of capacitors and switches in relation to a circuit according to the capacitance division method.
The aforementioned objects are achieved according to the invention by a switched-capacitor circuit comprising a plurality of sequentially-operated switched-capacitors. A first capacitor is arranged to be coupled and thereafter uncoupled to an input signal during a first time period. Thereby the first capacitor is charged to an input value in dependence on the input signal. A second capacitor is arranged to be coupled and thereafter uncoupled to the first capacitor during a second time period for charge distribution between the second and the first capacitor. Pairwise charge distribution is possibly done with further sequentially-operated switched capacitors. A final capacitor is arranged to be coupled and thereafter uncoupled to a previous capacitor during the final time period for charge distribution between the final and the previous capacitor. The switched-capacitor circuit further comprises means for selectively coupling the first and the second sequentially-operated switched-capacitors to an output circuit thereby enabling a desired weighting of the input signal to be attained.
The aforementioned objects are also achieved according to the invention by a switched-capacitor circuit comprising a plurality of sequentially-operated switched-capacitors. The capacitors are sequentially switched during a plurality of time periods. The circuit comprises at least a first, a second and a final sequentially-operated switched-capacitor. The first switched-capacitor is arranged to be coupled and thereafter uncoupled to an input signal during a first time period. The first switched-capacitor is thus charged to an input value in dependence on the input signal. The second switched-capacitor is arranged to be coupled and thereafter uncoupled to the first switched-capacitor during a second time period for charge distribution between the second and the first switched-capacitor. The charge is thus divided between the first and the second switched-capacitor. The second switched-capacitor becoming a previous switched-capacitor during the time period following the time period the second switched-capacitor received charge. The final switched-capacitor is arranged to be coupled and thereafter uncoupled to the previous switched-capacitor, in the minimum case this is the second switched-capacitor, during the final time period for charge distribution between the final and the previous switched-capacitor. The charge is thus divided between the final and the previous switched-capacitor. The switched-capacitor circuit further comprises means for selectively coupling the first and the second switched-capacitors to an output circuit thereby enabling a desired weighting of the input signal to be attained.
Advantageously, to achieve a higher weight factor resolution, the circuit further comprises a predetermined number of additional sequentially-operated switched-capacitors. The additional capacitors are arranged between the second switched-capacitor and the final switched-capacitor. Each additional sequentially-operated switched-capacitor is arranged to be coupled and thereafter uncoupled to a previous switched-capacitor during a time period for charge distribution between an additional switched-capacitor in question and the previous switched-capacitor. The charge is thus divided between the additional switched-capacitor in question and the previous switched-capacitor. The additional switched-capacitor in question becoming the previous switched-capacitor during the time period following the time period the additonal switched-capacitor in question received charge. The switched-capacitor circuit further comprises means for selectively coupling each additional sequentially-operated switched-capacitor to an output circuit.
Some embodiments of the switched capacitor circuit further comprises a first parallel-operated capacitor. The first parallel-operated capacitor is arranged to be coupled and thereafter be uncoupled to the input signal during the first time period. The first parallel-operated capacitor is not involved in any charge sharing with the sequentially-operated switched-capacitors. The circuit further comprises means for selectively coupling the first parallel-operated capacitor to an output circuit.
Advantageously each means for selectively coupling a sequentially-operated capacitor to an output circuit is for each capacitor in question selectively activated during a time period which is after a time period when the capacitor in question distributed its charge to a further capacitor.
Preferably each capacitor which is not coupled directly to the input signal is shorted at the latest during a time period before a time period in which a capacitor in question receives a charge distribution from a previous capacitor.
In certain embodiments the circuit is doubled into two identical branches, the operation of the branches being time shifted in relation to each other, thereby doubling the throughput rate. In some version the circuit is quadrupled into four identical branches, the operation of the branches being time shifted in relation to each other, thereby quadrupling the throu
Arvidsson Ragnar
Duppils Mattias
Eklund Jan-Erik
Burns Doane Swecker & Mathis L.L.P.
Le Dinh T.
Telefonaktiebolaget LM Ericsson (publ)
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