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 including a variable gain;
- 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 the variable gain 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.
A method for rejecting an image signal, the method comprising:
- processing a 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 configured with variable biasing including a variable gain;
- and
- wherein a quadrature portion of the signal is coupled to a second gm-C filter including at least a second gm-C filter configured with variable biasing;
- and
- controlling, using a bias controller coupled to the first gm-C filter stage and the second gm-C filter stage, the biasing and the variable gain 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.
Dependencies are inferred from the claim text.