Method and apparatus for reduced noise and carrier feedthrough in multimode transmitter

• US 7,688,880 B2
• Filed: 05/31/2006
• Issued: 03/30/2010
• Est. Priority Date: 05/31/2006
• Status: Active Grant

• Current Assignee: Spreadtrum Communications Inc (Tsinghua Holdings Co., Ltd.)
• Original Assignee: Spreadtrum Communications Inc (Tsinghua Holdings Co., Ltd.)
• Inventors: Ralston, Daniel Neil, Haub, David Ryan
• Primary Examiner(s): Payne; David C.
• Assistant Examiner(s): NGUYEN, LEON VIET Q
• Application Number:
  US11/421,200
• Publication Number:
  US 20070280338A1
• Time in Patent Office: 1,399 Days
• Field of Search: 455/127.4, 455/132, 455/552.1, 455/553.1, 375/144, 375/148
• US Class Current: 375/148
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes
• CPC Class Codes: H04L 27/362 Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated H04L27/366 takes precedence
• CPC Class Codes: H04L 27/366 Arrangements for compensating undesirable properties of the transmission path between the modulator and the demodulator

Abstract

A high dynamic range low noise direct conversion transmitter within a multimode apparatus having multiple transmit and receive operating modes is described. The direct conversion transmitter can include a digital baseband coupled to a low noise direct conversion stage. A high dynamic range current folding digital to analog converter can be used to convert the digital baseband signals to analog representations. A wide dynamic range variable gain baseband amplifier couples the baseband signal to the direct conversion stage. A controllable passive attenuation stage operates to provide further gain control. Carrier feedthrough can be substantially eliminated using a carrier feedthrough cancellation loop that selectively utilizes one of a plurality of receivers configured for one of the multiple receive modes.

Claims

1. A multimode apparatus configurable to support a plurality of communication standards, the apparatus comprising:

a first transceiver selectively configurable to support a first communication mode of the plurality of communication modes, the first transceiver including a first transmitter and a first receiver;

a second transceiver selectively configurable to support a second communication mode of the plurality of communication modes, the second transceiver including a second transmitter and a second receiver, and wherein the second receiver is configured to be a portion of a carrier feedthrough cancellation loop of the first transmitter when the multimode apparatus is configured to support the first communication mode;

an RF switch configured to couple an output of the first transmitter to an input of the second receiver when the multimode apparatus is configured to support the first communication mode; and

a carrier compensation module having an input coupled to an output of the second receiver when the multimode apparatus is configured to support the first communication mode, an output coupled to a baseband portion of the first transmitter, and configured to generate a carrier feedthrough cancellation signal based at least in part on a signal output by the second receiver,

wherein the carrier compensation module is configured to generate a DC offset value based on a DC value of the signal output by the second receiver, and sum the DC offset value with a baseband signal of the first transmitter.