Image rejection for low IF receivers
AssigneeFreescale Semiconductor, Inc.
InventorSateh Jalaleddine
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Abstract
A system that includes a polyphase filter comprises first and second gm-C filters with first and second variable biasing and a bias controller coupled to the first and second gm-C filters and configured to offset the first variable biasing and corresponding first gm of the first gm-C filter relative to the second variable biasing and corresponding second gm of the second gm-C filter to thus improve image rejection in the system. A corresponding method includes processing a signal in a complex polyphase filter and controlling biasing of the first gm-C filter stage relative to the second gm-C filter stage to provide a mismatched gm and thereby improve rejection of the image signal.
Claims20
A system that includes a polyphase filter, the system comprising:
- a first gm-C filter with first variable biasing;
- a second gm-C filter with second variable biasing;
- and
- a bias controller coupled to the first gm-C filter and the second gm-C filter and configured to offset the first variable biasing and a corresponding first gm of the first gm-C filter relative to-the second variable biasing and a corresponding second gm of the second gm-C filter to thereby improve image rejection in the system,
- wherein the bias controller is further configured to change a bias current in a gm cell, the gm cell including linearization circuitry.
A method for rejecting an image signal, the method comprising:
- processing a signal including the image signal in a complex polyphase filter;
- wherein an in phase portion of the signal is coupled to a first gm-C filter including at least a first gm-C filter stage configured with first variable biasing;
- and
- wherein a quadrature portion of the signal is coupled to a second gm-C filter including at least a second gm-C filter stage configured with a second-variable biasing;
- and
- controlling, using a bias controller coupled to the first gm-C filter stage and the second gm-C filter stage, the first variable biasing of the first gm-C filter stage relative to the second variable biasing of the second gm-C filter stage to provide a mismatched gm for one or more gms in the first gm-C filter relative to one or more gms in the second gm-C filter and thereby improve rejection of the image signal,
- wherein the controlling further comprises offsetting the first variable biasing relative to the second variable biasing to change a bias current in a gm cell, the gm cell including common mode rejection circuitry.
Dependencies are inferred from the claim text.