US20050025255A1 - DC offset cancellation - Google Patents
DC offset cancellation Download PDFInfo
- Publication number
- US20050025255A1 US20050025255A1 US10/924,996 US92499604A US2005025255A1 US 20050025255 A1 US20050025255 A1 US 20050025255A1 US 92499604 A US92499604 A US 92499604A US 2005025255 A1 US2005025255 A1 US 2005025255A1
- Authority
- US
- United States
- Prior art keywords
- offset
- demodulator
- modulator
- signal
- transmission
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Images
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/06—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
- H04L25/061—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset
- H04L25/063—Setting decision thresholds using feedback techniques only
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03C—MODULATION
- H03C3/00—Angle modulation
- H03C3/38—Angle modulation by converting amplitude modulation to angle modulation
- H03C3/40—Angle modulation by converting amplitude modulation to angle modulation using two signal paths the outputs of which have a predetermined phase difference and at least one output being amplitude-modulated
Definitions
- the present invention relates to offset cancellation in general and to DC offset cancellation in mobile communication systems in particular.
- the base band digital values are modulated onto a carrier high frequency signal and the combined signal is amplified before its transmission.
- the base band values may be complex values having real and imaginary components which are traditionally referred to as I and Q components, respectively.
- I and Q components are traditionally referred to as I and Q components, respectively.
- inaccuracies are introduced. These inaccuracies may cause the transmitter to interfere with signals on carrier frequencies allocated to other transmitters and therefore should be at least partially canceled by the transmitter.
- the DC offset mechanism is generally due to LO(t), which is caused due to leakage of the signal of a local oscillator (used for carrier modulation) into the demodulator output. The same problem occurs at the modulator side.
- FIG. 1 is a block diagram illustration of transmission and feedback paths of a mobile communication unit or a base station, in accordance with an embodiment of the present invention.
- FIG. 2 is a block diagram illustration of an alternative embodiment of the present invention.
- An algorithm is here, and generally, considered to be a self-consistent sequence of acts or operations leading to a desired result. These include physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers or the like. It should be understood, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities.
- Embodiments of the present invention may include apparatuses for performing the operations herein.
- This apparatus may be specially constructed for the desired purposes, or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer.
- a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions, and capable of being coupled to a computer system bus.
- FIG. 1 shows a transmission path 10 , a feedback path 12 and a DC offset estimator 16 .
- the transmission path 10 generally comprises some or all of the following elements: a baseband modulator 20 , a digital to analog (D/A) converter 24 , an IQ modulator 28 and a power amplifier 30 .
- Baseband modulator 20 converts an incoming bit stream into a baseband signal having I and Q components.
- D/A converter 24 converts the shaped digital signal into an analog signal.
- IQ modulator 28 modulates the complex baseband signal into a radio frequency (RF) signal and power amplifier 30 transmits the RF signal.
- RF radio frequency
- Feedback path 12 comprises some or all of the following elements: an attenuator 32 , an IQ demodulator 34 and an analog to digital (A/D) converter 40 .
- Attenuator 32 receives the transmitted radio frequency and IQ demodulator 34 converts the radio frequency signal into a baseband one.
- Analog to digital converter 40 converts the signal into a digital one.
- DC offset estimator 16 generally determines the DC offset due to IQ modulator 28 and IQ demodulator 34 from data from feedback path 12 .
- DC offset estimator 16 typically comprises a demodulator DC offset estimator 50 and an adaptive modulator DC offset estimator 52 .
- demodulator estimator 50 may receive the output V f of analog to digital converter 40 at predefined times.
- Demodulator estimator 50 may estimate the DC offset due to IQ demodulator 34 and the result, a signal labeled DC_DEMOD_EST, may be provided to a summer 56 in feedback path 12 .
- summer 56 may subtract the estimated DC offset, DC —DEMOD _EST, from the output of analog to digital converter 40 , thereby providing a signal from which most, if not all, of the DC offset due to IQ demodulator 34 has been removed.
- logical switch 54 provides its signal to demodulator estimator 50 during “non-transmission slots” (i.e. periods when no signal is being transmitted from or to the unit).
- a “zero” signal may be injected to the input of IQ demodulator 34 . This may be implemented by shutting down power amplifier 30 which results in an input to IQ demodulator 34 of generally zero. Thus, if there is any signal measured after analog to digital converter 40 , it is due to the DC offset of IQ demodulator 34 .
- the output of IQ demodulator 34 may be measured for a set number of consecutive symbols NO_SYMBOLS.
- the modulator DC offset may be calculated by operating both transmission path 10 and feedback path 12 .
- Transmission path 10 also includes a summer 60 , before FIR filter 22 , which may subtract the modulator DC offset, DC_MOD_EST, from the predistorted signal produced by multipliers 46 .
- PD LUT 42 is bypassed, typically by changing multipliers 46 to unity, and a zero input signal is provided (typically during a non-transmission slot) to baseband modulator 20 .
- adaptive modulator estimator 52 may assign initial values, typically obtained from a factory calibration, to summer 60 . The factory calibrated values may be far away from the true (and unknown) values due to thermal and frequency changes.
- the resultant signal is transmitted by power amplifier 30 and may be received by feedback path 12 , operating with logical switch 54 connecting analog to digital converter 40 to summer 56 .
- summer 56 produces two signals e I and e Q which are the feedback path output with the DC offset from IQ demodulator generally removed.
- a logical switch 58 may provide the two signals e I and e Q to adaptive modulator estimator 52 , which then operates to minimize the signals e I 2 and e Q 2 .
- DC_I_MOD_C old and DC_Q_MOD_C old are the previous values of offset estimation and initially may be the factory calibrated values.
- the selected iteration method is chosen as a tradeoff between the processing power of the transmitter and the required convergence speed of the output of adaptive estimator 52 . If fast convergence is required and the transmitter has a relatively high processing power level, a fast convergence method that requires dense computation (e. g., the quasi-Newton method) may be used. If, however, low processing power utilization is more important than fast convergence, simpler methods, such as the steepest descent method, may be used.
- phase rotation ⁇ circumflex over ( ⁇ ) ⁇ path along the path from the output of digital to analog converter 24 in transmission path 10 to the input to analog to digital converter 40 in feedback path 12 .
- the phase ⁇ circumflex over ( 100 ) ⁇ path is measured in the first transmission slot when data is transmitted.
- the angle ⁇ inp of the baseband input signal is measured, per symbol, as is the angle ⁇ out of each symbol of the signal V f after analog to digital converter 40 .
- the angle is defined as the angle in the complex plane of value ⁇ +j ⁇ tilde over (Q) ⁇ .
- phase ⁇ circumflex over ( ⁇ ) ⁇ path is the average value of the difference in the angles.
- ⁇ circumflex over ( ⁇ ) ⁇ path avg( ⁇ out ⁇ inp ) Equation 10
- the DC offset estimators 50 and 52 can be operated again. To do so, the data of the next non-transmitted slot is used. The DC offset estimators 50 and 52 are then operated on this data.
- FIG. 2 illustrates a further embodiment of the invention implemented in a transmitter having a predistorter. Elements, which are similar to those of FIG. 1 , have similar reference numerals.
- FIG. 2 shows transmission path 10 , feedback path 12 , a predistorter 14 and DC offset estimator 16 .
- the transmission path 10 generally comprises some or all of the following elements: baseband modulator 20 , a finite impulse response (FIR) filter 22 , digital to analog (D/A) converter 24 , an analog filter 26 , IQ modulator 28 and power amplifier 30 .
- FIR filter 22 shapes the baseband signal as desired.
- Analog filter 26 filters the analog signal as necessary.
- Feedback path 12 comprises some or all of the following elements: attenuator 32 , IQ demodulator 34 , a filter 36 and analog to digital (A/D) converter 40 .
- Filter 36 limits any noise to the bandwidth of the demodulated signal.
- Predistorter 14 comprises a predistorter (PD) lookup table (LUT) 42 and a PD 25 LUT trainer 44 .
- Pre-distorter 14 compensates for the non-linearity of power amplifier 30 and changes the signals entering power amplifier 30 such that the transmitted signals have substantially linear amplification (rather than the non-linear amplification, which occurs without the predistortion). Since the distortion changes due to temperature, aging and other characteristics of power amplifier 30 , the predistortion values are updated by PD LUT trainer 44 , based on feedback received from the output of power amplifier 30 .
- PD LUT 42 predistorts the signal from baseband modulator 20 in order to compensate for the distortion produced by power amplifier 30 . To do so, the output of PD LUT 42 is multiplied with the output of baseband modulator by multipliers 46 in transmission path 10 .
- PD LUT trainer 44 regularly updates the values of PD LUT 42 based on data received along feedback path 12 .
- PD LUT trainer 44 may receive signals with minimal, if any, demodulator DC offset and the transmitted signal may be both predistorted and may have the modulator DC offset removed.
- DC offset estimator 16 operates as described hereinabove. Specifically, it operates during non-transmission slots and PD LUT 42 is disabled by indicating to multipliers 46 to pass the output of baseband modulator 20 rather than multiplying it by the output of PD LUT 42 .
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Transmitters (AREA)
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
Abstract
A transmitter has a transmission path with an IQ modulator and a feedback path with an IQ demodulator. DC offset is determined by estimating a DC offset of the IQ demodulator, adaptively estimating a DC offset of the IQ modulator at least partially from the demodulator DC offset, subtracting the estimated demodulator DC offset from the feedback path and subtracting the estimated modulator DC offset from the transmission path.
Description
- The present invention is a continuation application of U.S. patent application Ser. No. 09/661,127, filed Sep. 13, 2000, which application is incorporated herein by reference.
- The present invention relates to offset cancellation in general and to DC offset cancellation in mobile communication systems in particular.
- Many transmitters transmit digital information values that are generated in base band. The base band digital values are modulated onto a carrier high frequency signal and the combined signal is amplified before its transmission. The base band values may be complex values having real and imaginary components which are traditionally referred to as I and Q components, respectively. In the modulation of the base band signal and amplification of the modulation signal, inaccuracies are introduced. These inaccuracies may cause the transmitter to interfere with signals on carrier frequencies allocated to other transmitters and therefore should be at least partially canceled by the transmitter.
- One source of inaccuracy is the IQ modulator and demodulator, which both suffer from a distortion mechanism called “local oscillator carrier feedthrough” and “DC offset”. For example, the output of the demodulator can be modeled as:
S(t)=I(t)cos(ωt)−Q(t)sin(ωt)+LO(t)Equation 1 - where:
LO(t)=A cos(ωt+φ)Equation 2 - The DC offset mechanism is generally due to LO(t), which is caused due to leakage of the signal of a local oscillator (used for carrier modulation) into the demodulator output. The same problem occurs at the modulator side.
- The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which:
-
FIG. 1 is a block diagram illustration of transmission and feedback paths of a mobile communication unit or a base station, in accordance with an embodiment of the present invention; and -
FIG. 2 is a block diagram illustration of an alternative embodiment of the present invention. - It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
- In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
- Some portions of the detailed description which follow are presented in terms of algorithms and symbolic representations of operations on data bits or binary digital signals within a computer memory. These algorithmic descriptions and representations may be the techniques used by those skilled in the data processing arts to convey the substance of their work to others skilled in the art.
- An algorithm is here, and generally, considered to be a self-consistent sequence of acts or operations leading to a desired result. These include physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers or the like. It should be understood, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities.
- Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.
- Embodiments of the present invention may include apparatuses for performing the operations herein. This apparatus may be specially constructed for the desired purposes, or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions, and capable of being coupled to a computer system bus.
- Reference is now made to
FIG. 1 , which generally illustrates elements used in transmission for both mobile communication units and the base stations with which they communicate. WhileFIG. 1 presents certain elements, it will be appreciated that other mobile units and base stations may or may not include all of the elements shown inFIG. 1 .FIG. 1 shows atransmission path 10, afeedback path 12 and aDC offset estimator 16. Thetransmission path 10 generally comprises some or all of the following elements: abaseband modulator 20, a digital to analog (D/A)converter 24, anIQ modulator 28 and apower amplifier 30.Baseband modulator 20 converts an incoming bit stream into a baseband signal having I and Q components. D/Aconverter 24 converts the shaped digital signal into an analog signal.IQ modulator 28 modulates the complex baseband signal into a radio frequency (RF) signal andpower amplifier 30 transmits the RF signal. -
Feedback path 12 comprises some or all of the following elements: anattenuator 32, anIQ demodulator 34 and an analog to digital (A/D)converter 40.Attenuator 32 receives the transmitted radio frequency andIQ demodulator 34 converts the radio frequency signal into a baseband one. Analog todigital converter 40 converts the signal into a digital one. -
DC offset estimator 16 generally determines the DC offset due toIQ modulator 28 andIQ demodulator 34 from data fromfeedback path 12.DC offset estimator 16 typically comprises a demodulatorDC offset estimator 50 and an adaptive modulatorDC offset estimator 52. Through alogical switch 54 infeedback path 12,demodulator estimator 50 may receive the output Vf of analog todigital converter 40 at predefined times.Demodulator estimator 50 may estimate the DC offset due toIQ demodulator 34 and the result, a signal labeled DC_DEMOD_EST, may be provided to asummer 56 infeedback path 12. Whenlogical switch 54 connects analog todigital converter 40 tosummer 56,summer 56 may subtract the estimated DC offset, DC—DEMOD_EST, from the output of analog todigital converter 40, thereby providing a signal from which most, if not all, of the DC offset due toIQ demodulator 34 has been removed. - Typically,
logical switch 54 provides its signal todemodulator estimator 50 during “non-transmission slots” (i.e. periods when no signal is being transmitted from or to the unit). At the same time, a “zero” signal, or one with a known sequence, may be injected to the input ofIQ demodulator 34. This may be implemented by shutting downpower amplifier 30 which results in an input toIQ demodulator 34 of generally zero. Thus, if there is any signal measured after analog todigital converter 40, it is due to the DC offset ofIQ demodulator 34. - The output of
IQ demodulator 34 may be measured for a set number of consecutive symbols NO_SYMBOLS. The two DC offset values DC_I_DEMOD_EST and DC_QDEMOD EST ofIQ demodulator 34 may be estimated as: - where Ĩ, {tilde over (Q)} are the real and imaginary parts, respectively, of the signal Vf produced by analog to
digital converter 40 and NO_SYMBOLS is the number of symbols used for averaging. In one embodiment, NO_SYMBOLS=5. - These two values may be provided to
summer 56 to generally cancel the DC offset ofIQ demodulator 34. - Once the demodulator DC offset has been estimated, the modulator DC offset may be calculated by operating both
transmission path 10 andfeedback path 12.Transmission path 10 also includes asummer 60, beforeFIR filter 22, which may subtract the modulator DC offset, DC_MOD_EST, from the predistorted signal produced bymultipliers 46. To determine the modulator DC offset,PD LUT 42 is bypassed, typically by changingmultipliers 46 to unity, and a zero input signal is provided (typically during a non-transmission slot) tobaseband modulator 20. In addition,adaptive modulator estimator 52 may assign initial values, typically obtained from a factory calibration, tosummer 60. The factory calibrated values may be far away from the true (and unknown) values due to thermal and frequency changes. - The resultant signal is transmitted by
power amplifier 30 and may be received byfeedback path 12, operating withlogical switch 54 connecting analog todigital converter 40 tosummer 56. The result is thatsummer 56 produces two signals eI and eQ which are the feedback path output with the DC offset from IQ demodulator generally removed. During non-transmission slots, the two signals may be given mathematically as:
e I =Ĩ−DC — I_DEMOD_EST, Equation 5
e Q ={tilde over (Q)}−DC — Q_DEMOD_EST, Equation 6
where Ĩ, {tilde over (Q)} are defined hereinabove. - When determining the DC offset of
IQ modulator 28, alogical switch 58 may provide the two signals eI and eQ toadaptive modulator estimator 52, which then operates to minimize the signals eI 2 and e Q 2. - At the end of each symbol period,
adaptive modulator estimator 52 may compute:
DC— I_MOD— C new=DC— I_MOD— C old−μIRe{e I rot}, Equation 7
for the I channel and
DC— Q_MOD— C new=DC— Q_MOD— C old−μQIm{e Q rot}, Equation 8
for the Q channel, where μI, μQ, are the step sizes which control the rate of adaptation, 0≦μI≦1, 0≦μQ≦1 and eI rot and eQ rot are rotated errors given hereinbelow by Equation 9. DC_I_MOD_Cold and DC_Q_MOD_Cold are the previous values of offset estimation and initially may be the factory calibrated values. - Alternatively to using the steepest descent iteration method (implemented in Equation 7 and Equation 8), other iteration methods as are known from optimization theory, such as the conjugate gradient equation and the quasi-Newton equation, may be used to minimize the signals eI 2 and eQ 2. In some embodiments of the invention, the selected iteration method is chosen as a tradeoff between the processing power of the transmitter and the required convergence speed of the output of
adaptive estimator 52. If fast convergence is required and the transmitter has a relatively high processing power level, a fast convergence method that requires dense computation (e. g., the quasi-Newton method) may be used. If, however, low processing power utilization is more important than fast convergence, simpler methods, such as the steepest descent method, may be used. - There is often a phase rotation {circumflex over (φ)}path along the path from the output of digital to
analog converter 24 intransmission path 10 to the input to analog todigital converter 40 infeedback path 12. This phase rotation can be estimated as described hereinbelow with respect toEquation 10 and then used to rotate the errors eI and eQ according to:
e I rot =e I e −j{circumflex over (φ)}path ,
e Q rot =e Q e −j{circumflex over (100 )}path , Equation 9 - The phase {circumflex over (100 )}path is measured in the first transmission slot when data is transmitted. The angle θinp of the baseband input signal is measured, per symbol, as is the angle θout of each symbol of the signal Vf after analog to
digital converter 40. The angle is defined as the angle in the complex plane of value Ĩ+j{tilde over (Q)}. - The phase {circumflex over (φ)}path is the average value of the difference in the angles. Thus:
{circumflex over (φ)}path=avg(θout−θinp)Equation 10 - Dunng regular operation,
logical switches summers feedback path 12 produces signals with minimal, if any, demodulator DC offset and the transmitted signal may have the modulator DC offset removed. - If desired, and particularly during long transmission periods, the DC offset
estimators estimators - Reference is now made to
FIG. 2 , which illustrates a further embodiment of the invention implemented in a transmitter having a predistorter. Elements, which are similar to those ofFIG. 1 , have similar reference numerals. -
FIG. 2 showstransmission path 10,feedback path 12, apredistorter 14 and DC offsetestimator 16. Thetransmission path 10 generally comprises some or all of the following elements:baseband modulator 20, a finite impulse response (FIR)filter 22, digital to analog (D/A)converter 24, ananalog filter 26,IQ modulator 28 andpower amplifier 30.FIR filter 22 shapes the baseband signal as desired.Analog filter 26 filters the analog signal as necessary. -
Feedback path 12 comprises some or all of the following elements:attenuator 32,IQ demodulator 34, afilter 36 and analog to digital (A/D)converter 40.Filter 36 limits any noise to the bandwidth of the demodulated signal. -
Predistorter 14 comprises a predistorter (PD) lookup table (LUT) 42 and a PD 25LUT trainer 44.Pre-distorter 14 compensates for the non-linearity ofpower amplifier 30 and changes the signals enteringpower amplifier 30 such that the transmitted signals have substantially linear amplification (rather than the non-linear amplification, which occurs without the predistortion). Since the distortion changes due to temperature, aging and other characteristics ofpower amplifier 30, the predistortion values are updated byPD LUT trainer 44, based on feedback received from the output ofpower amplifier 30. - During regular transmission,
PD LUT 42 predistorts the signal frombaseband modulator 20 in order to compensate for the distortion produced bypower amplifier 30. To do so, the output ofPD LUT 42 is multiplied with the output of baseband modulator bymultipliers 46 intransmission path 10.PD LUT trainer 44 regularly updates the values ofPD LUT 42 based on data received alongfeedback path 12. - During regular operation,
logical switches summers PD LUT trainer 44 may receive signals with minimal, if any, demodulator DC offset and the transmitted signal may be both predistorted and may have the modulator DC offset removed. - DC offset
estimator 16 operates as described hereinabove. Specifically, it operates during non-transmission slots andPD LUT 42 is disabled by indicating tomultipliers 46 to pass the output ofbaseband modulator 20 rather than multiplying it by the output ofPD LUT 42. - The methods and apparatus disclosed herein have been described without reference to specific hardware or software. Rather, the methods and apparatus have been described in a manner sufficient to enable persons of ordinary skill in the art to readily adapt commercially available hardware and software as may be needed to reduce any of the embodiments of the present invention to practice without undue experimentation and using conventional techniques.
- It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the invention is defined by the claims that follow:
Claims (11)
1. A method of adaptively estimating a DC offset of an IQ modulator, the method comprising:
providing a predetermined signal to an input of said IQ modulator and transmitting said signal;
estimating a DC offset of an IQ demodulator from a received version of said signal;
generating a difference signal between said received signal and said estimated DC offset of said IQ demodulator; and
subtracting a modified rotated version of said difference signal from a previous value of said DC offset of said IQ modulator.
2. A method according to claim 1 , further comprising:
estimating a phase rotation of a transmission path of a transmitter and a feedback path of said transmitter; and
modifying said difference signal with said phase rotation.
3. A method according to claim 1 , wherein said estimating said DC offset of said IQ demodulator is undertaken during non-transmission slots.
4. A transmitter comprising:
a transmission path having an IQ modulator;
a feedback path having an IQ demodulator;
a demodulator DC offset estimator to average a received signal along said feedback path and to estimate a DC offset of said IQ demodulator; and
an adaptive modulator DC offset estimator to estimate a DC offset of said IQ modulator at least partially from said DC offset of said IQ demodulator,
wherein said adaptive modulator DC offset estimator is to generate a difference signal between said received signal and said DC offset of said IQ demodulator and to subtract a modified rotated version of said difference signal from a previous value of said DC offset of said IQ modulator.
5. A transmitter according to claim 4 , wherein said demodulator DC offset estimator and said adaptive modulator DC offset estimator are to operate during non-transmission slots.
6. A transmitter according to claim 5 , wherein said non-transmission slots are non-transmission slots of regular transmission.
7. A transmitter according to claim 4 , wherein said adaptive modulator DC offset estimator is to modify said difference signal with a phase rotation of said transmission and feedback paths.
8. An integrated circuit having a transmitter, the transmitter comprising:
a transmission path having an IQ modulator;
a feedback path having an IQ demodulator;
a demodulator DC offset estimator to average a received signal along said feedback path and to estimate a DC offset of said IQ demodulator;
an adaptive modulator DC offset estimator to estimate a DC offset of said IQ modulator by generating a difference signal between said received signal and said demodulator DC offset and subtracting a modified rotated version of said difference signal from a previous value of said DC offset of said IQ modulator.
9. An integrated circuit according to claim 8 , wherein said demodulator DC offset estimator and said adaptive modulator DC offset estimator are to operate during non-transmission slots.
10. An integrated circuit according to claim 9 , wherein said non-transmission slots are non-transmission slots of regular transmission.
11. An integrated circuit according to claim 8 , wherein said adaptive modulator DC offset estimator is to modify said difference signal with a phase rotation of said transmission and feedback paths.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/924,996 US20050025255A1 (en) | 2000-09-13 | 2004-08-25 | DC offset cancellation |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/661,127 US6801581B1 (en) | 2000-09-13 | 2000-09-13 | DC offset cancellation |
US10/924,996 US20050025255A1 (en) | 2000-09-13 | 2004-08-25 | DC offset cancellation |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/661,127 Continuation US6801581B1 (en) | 2000-09-13 | 2000-09-13 | DC offset cancellation |
Publications (1)
Publication Number | Publication Date |
---|---|
US20050025255A1 true US20050025255A1 (en) | 2005-02-03 |
Family
ID=33030227
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/661,127 Expired - Fee Related US6801581B1 (en) | 2000-09-13 | 2000-09-13 | DC offset cancellation |
US10/924,996 Abandoned US20050025255A1 (en) | 2000-09-13 | 2004-08-25 | DC offset cancellation |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/661,127 Expired - Fee Related US6801581B1 (en) | 2000-09-13 | 2000-09-13 | DC offset cancellation |
Country Status (1)
Country | Link |
---|---|
US (2) | US6801581B1 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20100048149A1 (en) * | 2008-08-21 | 2010-02-25 | Tang Clive K | Techniques for Adaptive Predistortion Direct Current Offset Correction in a Transmitter |
US20100118999A1 (en) * | 2008-11-07 | 2010-05-13 | Nec Electronics Corporation | Communication apparatus and offset canceling method |
EP2318600A1 (en) * | 2008-08-08 | 2011-05-11 | S.C. Johnson & Son, Inc. | Fluid dispenser |
US8437385B1 (en) * | 2012-02-24 | 2013-05-07 | National Instruments Corporation | Measuring the DC properties of a signal path between transmitter and receiver |
Families Citing this family (19)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7177366B1 (en) * | 2001-09-06 | 2007-02-13 | The Board Of Trustees Of The Leland Stanford Junior University | Automatic phase alignment for high-bandwidth cartesian-feedback power amplifiers |
US7450631B2 (en) * | 2001-10-26 | 2008-11-11 | Intel Corporation | Metric correction for multi user detection, for long codes DS-CDMA |
KR100448892B1 (en) * | 2002-06-04 | 2004-09-18 | 한국전자통신연구원 | Apparatus and Method for Pre-distortion for Nonlinear Distortion of High Power Amplifier |
US7412006B2 (en) * | 2003-07-24 | 2008-08-12 | Freescale Semiconductor, Inc. | Method and apparatus for RF carrier feedthrough suppression |
US7280612B2 (en) * | 2003-07-25 | 2007-10-09 | Zarbana Digital Fund Llc | Digital branch calibrator for an RF transmitter |
KR100548407B1 (en) * | 2003-09-17 | 2006-02-02 | 엘지전자 주식회사 | Method for removing dc offset of transmitting signal |
US7457379B2 (en) * | 2003-10-16 | 2008-11-25 | Broadcom Corporation | Adaptive multi-step combined DC offset compensation for EDGE 8-PSK |
US7526266B2 (en) * | 2005-02-14 | 2009-04-28 | Intelleflex Corporation | Adaptive coherent RFID reader carrier cancellation |
CN1854234B (en) | 2005-04-21 | 2013-03-20 | 安集微电子(上海)有限公司 | Polished sizing material, its use and using method |
US7653147B2 (en) * | 2005-08-17 | 2010-01-26 | Intel Corporation | Transmitter control |
TWI311244B (en) * | 2006-04-07 | 2009-06-21 | Hon Hai Prec Ind Co Ltd | System for cancelling dc offset |
US20080243047A1 (en) * | 2007-03-27 | 2008-10-02 | Babaev Eilaz P | Ultrasound wound care device |
JP5092982B2 (en) * | 2008-08-12 | 2012-12-05 | 富士通株式会社 | DC offset correction apparatus and method |
US8755756B1 (en) | 2009-04-29 | 2014-06-17 | Qualcomm Incorporated | Active cancellation of interference in a wireless communication system |
US8331485B2 (en) * | 2009-07-08 | 2012-12-11 | Qualcomm Incorporated | Spur cancellation in a digital baseband transmit signal using cancelling tones |
US8358164B2 (en) * | 2010-11-30 | 2013-01-22 | Infineon Technologies Ag | Square wave signal component cancellation |
US8615204B2 (en) | 2011-08-26 | 2013-12-24 | Qualcomm Incorporated | Adaptive interference cancellation for transmitter distortion calibration in multi-antenna transmitters |
US9025648B2 (en) * | 2013-02-22 | 2015-05-05 | Tektronix, Inc. | Measurement of DC offsets in IQ modulators |
US20140269985A1 (en) * | 2013-03-14 | 2014-09-18 | Analog Devices Technology | Dc bias estimation of a radio frequency mixer |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5751114A (en) * | 1996-05-24 | 1998-05-12 | International Business Machines Corporation | Apparatus, method and article of manufacture for carrier frequency compensation in a FM radio transmitter |
US5761259A (en) * | 1996-05-24 | 1998-06-02 | International Business Machines Corporation | Apparatus, method and article of manufacture for carrier frequency compensation in a FM radio |
US20020191713A1 (en) * | 2000-01-28 | 2002-12-19 | Mcvey James D. | Modulation system having on-line IQ calibration |
US6741662B1 (en) * | 2000-04-17 | 2004-05-25 | Intel Corporation | Transmitter linearization using fast predistortion |
Family Cites Families (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS647969A (en) * | 1987-06-29 | 1989-01-11 | Ueki Kokan Shokai Kk | Device for producing coated steel deck or the like |
US4878029A (en) * | 1988-12-05 | 1989-10-31 | General Electric Company | Complex digital sampling converter for demodulator |
US5870668A (en) * | 1995-08-18 | 1999-02-09 | Fujitsu Limited | Amplifier having distortion compensation and base station for radio communication using the same |
JP3549963B2 (en) * | 1995-11-02 | 2004-08-04 | 三菱電機株式会社 | Digital radio receiver |
US6018650A (en) | 1996-12-18 | 2000-01-25 | Aironet Wireless Communications, Inc. | Cellular communication devices with automated power level adjust |
FI107212B (en) * | 1999-03-26 | 2001-06-15 | Nokia Networks Oy | I / Q modulator DC offset correction |
US6504884B1 (en) * | 1999-05-12 | 2003-01-07 | Analog Devices, Inc. | Method for correcting DC offsets in a receiver |
JP4360739B2 (en) * | 1999-05-24 | 2009-11-11 | 株式会社アドバンテスト | Quadrature demodulation apparatus, method, and recording medium |
US6606359B1 (en) * | 2000-07-26 | 2003-08-12 | Motorola, Inc | Area-optimum rapid acquisition cellular multi-protocol digital DC offset correction scheme |
-
2000
- 2000-09-13 US US09/661,127 patent/US6801581B1/en not_active Expired - Fee Related
-
2004
- 2004-08-25 US US10/924,996 patent/US20050025255A1/en not_active Abandoned
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5751114A (en) * | 1996-05-24 | 1998-05-12 | International Business Machines Corporation | Apparatus, method and article of manufacture for carrier frequency compensation in a FM radio transmitter |
US5761259A (en) * | 1996-05-24 | 1998-06-02 | International Business Machines Corporation | Apparatus, method and article of manufacture for carrier frequency compensation in a FM radio |
US20020191713A1 (en) * | 2000-01-28 | 2002-12-19 | Mcvey James D. | Modulation system having on-line IQ calibration |
US6741662B1 (en) * | 2000-04-17 | 2004-05-25 | Intel Corporation | Transmitter linearization using fast predistortion |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP2318600A1 (en) * | 2008-08-08 | 2011-05-11 | S.C. Johnson & Son, Inc. | Fluid dispenser |
US20100048149A1 (en) * | 2008-08-21 | 2010-02-25 | Tang Clive K | Techniques for Adaptive Predistortion Direct Current Offset Correction in a Transmitter |
US8412132B2 (en) | 2008-08-21 | 2013-04-02 | Freescale Semiconductor, Inc. | Techniques for adaptive predistortion direct current offset correction in a transmitter |
US20100118999A1 (en) * | 2008-11-07 | 2010-05-13 | Nec Electronics Corporation | Communication apparatus and offset canceling method |
US8320482B2 (en) * | 2008-11-07 | 2012-11-27 | Renesas Electronics Corporation | Communication apparatus and offset canceling method |
US8437385B1 (en) * | 2012-02-24 | 2013-05-07 | National Instruments Corporation | Measuring the DC properties of a signal path between transmitter and receiver |
US8654828B2 (en) | 2012-02-24 | 2014-02-18 | National Instruments Corporation | Mechanism for the measurement of DC properties of a signal path |
Also Published As
Publication number | Publication date |
---|---|
US6801581B1 (en) | 2004-10-05 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US6801581B1 (en) | DC offset cancellation | |
US6771709B2 (en) | System and method for direct transmitter self-calibration | |
EP1224733B1 (en) | Adaptive linearization of power amplifiers | |
EP0881807B1 (en) | Tansmitter with linearised amplifier | |
KR100539874B1 (en) | Method and apparatus for self-calibrating in a mobile transceiver | |
US7409004B2 (en) | Hybrid polar modulator differential phase Cartesian feedback correction circuit for power amplifier linearization | |
US8009765B2 (en) | Digital polar transmitter | |
US6252912B1 (en) | Adaptive predistortion system | |
US8026762B2 (en) | High efficiency transmitter for wireless communication | |
US7596125B2 (en) | Adjusting the amplitude and phase characteristics of transmitter generated wireless communication signals in response to base station transmit power control signals and known transmitter amplifier characteristics | |
US7409007B1 (en) | Method and apparatus for reducing adjacent channel power in wireless communication systems | |
US20030197558A1 (en) | Adaptive predistortion system and a method of adaptively predistorting a signal | |
JPH1032435A (en) | Method for correcting nonlinearity of amplifier and radio transmitter using the method | |
JPH1013160A (en) | Method for correcting nonlinearity of amplifier and radio transmitter using the method | |
WO2004095715A2 (en) | Additive digital predistortion system employing parallel path coordinate conversion | |
US20130177105A1 (en) | Method and system for estimating and compensating non-linear distortion in a transmitter using calibration | |
US8090036B2 (en) | Transmitter and carrier leak detection method | |
KR20060064603A (en) | Method and system for suppressing carrier leakage | |
US7877060B1 (en) | Fast calibration of AM/PM pre-distortion | |
US7248642B1 (en) | Frequency-dependent phase pre-distortion for reducing spurious emissions in communication networks | |
JP2001507196A (en) | Pre-adaptive distortion application method | |
EP2954612B1 (en) | Signal predistortion by addition of a correction term depending on a predefined constellation symbol, a transmission model and a target constellation symbol | |
Nuñez Perez et al. | FPGA‐based system for effective IQ imbalance mitigation of RF power amplifiers | |
US7263136B2 (en) | Predistortion modulator | |
US20050201487A1 (en) | Pre-distortion method, measurement arrangement, pre-distorter structure, transmitter, receiver and connecting device |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: INTEL CORPORATION, CALIFORNIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:D.S.P.C. TECHNOLOGIES LTD.;REEL/FRAME:015755/0213 Effective date: 20030501 Owner name: D.S.P.C. TECHNOLOGIES LTD., ISRAEL Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FRANCOS, AMIR;BARAK, ILAN;YELLIN, DANIEL;REEL/FRAME:015753/0668 Effective date: 20010101 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |