METHOD AND APPARATUS FOR REDUCED NOISE AND CARRIER FEEDTHROUGH IN MULTIMODE TRANSMITTER

• US 20070280338A1
• Filed: 05/31/2006
• Published: 12/06/2007
• Est. Priority Date: 05/31/2006
• Status: Active Grant

• Current Assignee: Spreadtrum Communications USA
• Original Assignee: Quorum Systems, Inc. (Spreadtrum Communications USA)
• Inventors: Haub, David Ryan, Ralston, Daniel Neil
• Granted Patent: US 7,688,880 B2
• Time in Patent Office: Days
• US Class Current: 375/222
• 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 configured to support a first communication mode of the plurality of communication modes, the first transceiver including a first transmitter and a first receiver; and

a second receiver selectively configurable to support one of a second communication mode or a carrier feedthrough cancellation loop of the first transmitter.

2. The apparatus of claim 1, further comprising a carrier compensation module having an input coupled to an output of the second receiver when the second receiver is selectively configured to support the carrier feedthrough cancellation loop, 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.

3. The apparatus of claim 2, wherein the carrier compensation module is configured to determine a DC offset value to compensate for a carrier feedthrough of the first transmitter.

4. The apparatus of claim 2, wherein the carrier compensation module is configured to determine the carrier feedthrough cancellation signal based at least in part on a DC value of the signal output by the second receiver.

5. The apparatus of claim 4, wherein the carrier compensation module is configured to minimize the DC value of the signal output by the second receiver.

6. The apparatus of claim 1, further comprising a switch having a first input coupled to an RF output of the first transmitter and a second input coupled to a second receive input, and configured to couple the RF output of the first transmitter to an input of the second receiver when the second receiver is selectively configured to support the carrier feedthrough cancellation loop.

7. The apparatus of claim 1, wherein the first transmitter comprises:

a frequency translation stage;

a Local Oscillator (LO) having an output coupled to an input of the frequency conversion stage; and

an LO switch having an input coupled to the output of the LO and configured to selectively couple the LO to a frequency translation stage of the second receiver when the second receiver is selectively configured to support the carrier feedthrough cancellation loop.

8. The apparatus of claim 1, wherein the second receiver is configured to frequency translate a carrier signal at an output of the first transmitter to a DC signal when the second receiver is selectively configured to support the carrier feedthrough cancellation loop.

9. The apparatus of claim 1, wherein the first transmitter comprises:

an Analog to Digital Converter (ADC) configured to receive a baseband signal and convert the baseband signal to a digital representation;

a digital gain module having an input coupled to the ADC and configured to apply a digital gain to the digital representation;

a DC offset control module coupled to an output of the digital gain module and configured to sum a carrier feedthrough cancellation signal from the carrier feedthrough cancellation loop to a signal output from the digital gain module; and

a Digital to Analog Converter (DAC) coupled to the DC offset control module and configured to generate an analog signal representation.

10. The apparatus of claim 9, wherein the DAC comprises a current folding DAC.

11. The apparatus of claim 9, wherein the first transmitter further comprises:

a frequency translation module coupled to the DAC and configured to frequency convert the analog signal representation to a desired RF; and

an attenuator coupled to the frequency translation module and configured to provide a controllable attenuation.

12. The apparatus of claim 1, wherein the first communication mode comprises a full duplex communication mode.

13. The apparatus of claim 1, wherein the first communication mode comprises a Code Division Multiple Access (CDMA) communication mode.

14. The apparatus of claim 1, wherein the second communication mode comprises a Time Division Multiple Access (TDMA) communication mode.

15. The apparatus of claim 1, wherein the multimode apparatus comprises a single semiconductor substrate.

16. 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; and

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.

17. The apparatus of claim 16, further comprising:

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.

18. The apparatus of claim 17, 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.

19. A method of canceling carrier feedthrough in a direct conversion transmitter of a multimode communication apparatus, the method comprising:

determining a communication mode of the multimode communication apparatus from a plurality of communication modes;

configuring a transceiver for the communication mode; and

configuring a receiver distinct from the transceiver as part of a carrier feedthrough cancellation loop when the communication mode is a full duplex communication mode.

20. The method of claim 19, further comprising controlling the receiver to a low power state if the first communication mode is not a full duplex communication mode.

21. The method of claim 19, further comprising controlling the receiver to for the communication mode when the communication mode is not a full duplex communication mode.

22. The method of claim 19, wherein configuring the receiver as part of the carrier feedthrough cancellation loop comprises:

coupling a transmitter output from the transceiver to an input of the receiver; and

configuring the receiver to frequency convert a signal at a carrier frequency at the transmitter output to a DC signal.

23. The method of claim 19, further comprising:

determining a DC value at the output of the second receiver; and

varying a DC offset value applied to a baseband signal of the first transceiver based on the DC value.

24. A method of canceling carrier feedthrough in a direct conversion transmitter of a multimode communication apparatus, the method comprising:

receiving an analog baseband signal;

digitizing the baseband signal to generate a digital representation;

applying a digital gain to the digital representation to generate an amplified digital representation;

combining a DC offset to the amplified digital representation;

converting the amplified digital representation with the DC offset to an analog representation; and

frequency converting the analog representation to an RF signal.

25. The method of claim 24, wherein combining the DC offset to the amplified digital representation comprises:

coupling a first transmitter output to a receiver selectively configurable to process the output from the first transmitter or a communication mode distinct from a communication mode supported by the first transmitter;

downconverting a signal at the first transmitter output to a DC value;

determining the DC offset that minimizes the DC value; and

summing the DC offset to the amplified digital representation.

26. The method of claim 24, wherein converting the amplified digital representation with the DC offset comprises performing a digital to analog conversion with a current folding DAC.

27. The method of claim 24, wherein frequency converting the analog representation comprises mixing the analog representation with a Local Oscillator (LO) signal to frequency translate the analog representation to the RF signal.

28. The method of claim 24, selectively attenuating the RF signal with a controllable attenuator.

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

means for determining a communication mode of the multimode communication apparatus from a plurality of communication modes;

means for configuring a transceiver for the communication mode; and

means for configuring a receiver distinct from the transceiver as part of a carrier feedthrough cancellation loop when the communication mode is a full duplex communication mode.

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

means for transmitting a transmit RF signal according to a first communication mode;

means for receiving a receive RF signal according to the first communication mode; and

means selectively reconfigurable for one of receiving a receive RF signal according to a second communication mode or determining a carrier feedthrough cancellation signal of the means for transmitting.

31. A method of canceling carrier feedthrough in a direct conversion transmitter of a multimode communication apparatus, the method comprising:

coupling a first transmitter output to a receiver selectively configurable to process the output from the first transmitter or a communication mode distinct from a communication mode supported by the first transmitter;

downconverting a signal at the first transmitter output to a DC value;

determining a DC offset that minimizes the DC value; and

summing the DC offset to the amplified digital representation.

32. The method of claim 31, wherein determining the DC offset comprises:

injecting a test DC offset value to a baseband signal of the first transmitter;

downconverting a test signal at the first transmitter to a test DC value to establish a threshold;

comparing the DC value to the threshold; and

mapping a result of the comparison to in-phase (I) and quadrature (Q) DC offset values from a look up table.

33. The method of claim 32, wherein determining the DC offset further comprises:

storing the I and Q DC offset values as offset correction values;

reducing the test DC offset value;

generating an updated threshold based on the reduced test DC offset value;

comparing the DC value to the updated threshold; and

updating the offset correction values based on the comparison.