Low noise switched low pass filter with benign transients
AssigneeNorthrop Grumman Corporation
InventorGerald R. Fischer
Life of this patent
Estimating the term…
Abstract
A switched low pass filter (18) minimizes transients generated during filter switching events and eliminates active circuit random noise. The switched low pass filter (18) includes a filter input terminal (26) for receiving an input base band signal, and an RC circuit (R1, C1, S1, S2) for receiving the input base band signal and for passing only a filtered portion of the input base band signal depending on a wide, mid or narrow band mode of filter operation. The switched low pass filter (18) also includes a transient reduction circuit (34) in switchable communication with the RC circuit (R1, C1, S1, S2) for minimizing transients and switching events caused by transitioning to the mid and narrow band modes of filter operation.
Claims21
A switched low pass filter comprising:
- a filter input terminal for the receiving an input base band signal;
- an RC circuit for receiving the input base band signal and for passing only a filtered portion of the input base band signal depending on a wide, mid or narrow band mode of filter operation;
- a transient reduction circuit including an active circuit element, the transient reduction circuit in switchable communication with the RC circuit for minimizing transients and switching events caused by transforming to the mid and narrow band modes of filter operation, and for eliminating active circuit random noise by disconnecting an output of the active circuit element from the RC circuit during the narrow band mode of operation;
- and
- a filter output terminal for outputting the input base band signal in the wide band mode of operation, and the filtered portion of the base band signal subsequent to the transient reduction circuit minimizing the transients and the switching events caused by transitioning to the mid and narrow band modes of filter operation.
A switched low pass filler comprising:
- an RC circuit for filtering an input be rid signal and including both an RC circuit resistor and an RC circuit capacitor;
- a transient reduction circuit coupled to the RC circuit for switching the RC circuit to a wide band mode of operation to accommodate acquisition of a new input signal to charge the RC circuit capacitor, for subsequently switching the RC circuit to a mid band mode of operation to transition the circuit from the wide band mode of operation to maintain a charge on the RC circuit capacitor accumulated during the wide band mode of operation, and for subsequently switching the RC circuit to a narrow band steady state mode of operation, the transient reduction circuit thereby minimizing transients caused by switching the RC circuit to the mid and narrow band modes of operation,
- wherein the transient reduction circuit includes an active circuit element, and wherein the transient reduction circuit decouples and output of the active circuit element from the RC circuit when switching the RC circuit to the narrow band steady state mode of operation to thereby eliminate active circuit random noise.
Dependencies are inferred from the claim text.