Method and apparatus for minimizing baseband offset error in a receiver
First Claim
Patent Images
1. A dc averaging technique for a direct conversion receiver, comprising the steps of:
- receiving a radio frequency (RF) signal;
converting the received RF signal to a baseband signal, the baseband signal being subject to dc offset caused by a plurality of dc error sources;
calculating discrete dc error values independent of the plurality of dc error sources, over a variable number of samples using piece-wise continuous dc averaging to generate a dc compensation value;
updating the dc compensation value as a fixed value for each sample to approximate a high pass filter response with an equivalent corner;
applying the updated dc compensation value to the baseband signal;
wherein the step of updating the dc compensation value includes adjusting an alpha factor, used in the discrete error calculation, based on an allowable integration period and targeted accuracy.
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Abstract
An adaptive dc compensation technique (100) eliminates dc error for both digital and constant envelope modulation protocols (108). For analog modulation, a dc averaging technique utilizes piece-wise continuous dc averaging (110) that calculates discrete dc error values over a variable number of samples (112) and updates the dc compensation value as a fixed value for a specified sample length (114). The piece-wise “update-and-hold” technique (110) results in a pseudo high pass filter response with an equivalent corner. For digital modulation, a continuous high pass filter section of the receiver is enabled (120).
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Citations
11 Claims
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1. A dc averaging technique for a direct conversion receiver, comprising the steps of:
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receiving a radio frequency (RF) signal; converting the received RF signal to a baseband signal, the baseband signal being subject to dc offset caused by a plurality of dc error sources; calculating discrete dc error values independent of the plurality of dc error sources, over a variable number of samples using piece-wise continuous dc averaging to generate a dc compensation value; updating the dc compensation value as a fixed value for each sample to approximate a high pass filter response with an equivalent corner; applying the updated dc compensation value to the baseband signal; wherein the step of updating the dc compensation value includes adjusting an alpha factor, used in the discrete error calculation, based on an allowable integration period and targeted accuracy. - View Dependent Claims (2, 3, 4)
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5. A method of compensating dc offset error in a direct conversion receiver, comprising:
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receiving a Radio Frequency (RF) signal; converting the RF signal to a baseband signal; sampling the baseband signal over a sampling period of variable sample lengths; determining whether the received RF signal incorporates analog or digital modulation; for received RF signals incorporating analog modulation, implementing piece-wise continuous averaging comprised of; calculating discrete dc error values for each sample period; updating a dc compensation value as a fixed value for each sample period based on the discrete dc error values for each period; holding the dc compensation value for a particular sample period constant for that sample period; and for received RF signals incorporating digital modulation, disabling the piece-wise continuous averaging; and enabling a continuous high pass filter section of the receiver with corner sufficiently low to eliminate baseband dc errors response for digital protocols.
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6. An apparatus for compensating dc offset in a direct conversion receiver, including:
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means for converting an RF signal to a baseband signal, the baseband signal being subject to dc offset caused by a plurality of dc error sources; an amplifier for amplifying the baseband signal and providing an amplified signal; a low pass filter for filtering the amplified signal to provide a filtered signal; an analog-to-digital converter for converting the filtered signal to a digital signal; an integrator for sampling the digital signal over a sample period of variable lengths and calculating a discrete integrated dc error value for the sample period, regardless of the dc error source; a controller for receiving the calculated dc error value and updating and holding an updated dc compensation value as a fixed value for each period based on the discrete error value for each period; a digital signal processor for triggering the controller to update the dc compensation value; and a digital-to-analog converter for converting the updated dc compensation value to an analog signal to be applied to the baseband signal.
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7. A method for minimizing baseband offset error in a receiver, including the step of:
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receiving a radio frequency (RF) signal; converting the RF signal to a baseband signal; determining a modulation protocol of the received RF signal as being one of;
digital modulation and analog modulation;initiating a dc compensation value based on the modulation protocol; for the analog modulation protocol; holding the dc compensation value constant while initiating continuous piece-wise dc error correction to reduce error in the baseband signal; and for the digital modulation protocol; enabling a hardware dc offset correction in response to a second set of signal conditions to reduce error in the baseband signal. - View Dependent Claims (8, 9)
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10. A method of compensating dc offset error in a direct conversion receiver, comprising:
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receiving a radio frequency (RF) signal having an operating protocol; measuring an initial dc hardware offset error; performing an initial hardware dc offset correction using preset default DSP parameters;
alpha, integration period, update rate, and step size (a, Tp, Tu, and S respectively);determining whether the operating protocol is analog or digital; scaling the dc offset based on the operating protocol; resetting the DSP parameters based on the operating protocol; initiating I/Q integration to determine dc offset error; calculating an I/Q dc compensation value based on the determined dc offset error; comparing the calculated I/Q dc compensation value to a maximum dc update step size provided by the reset DSP parameter, S; updating the dc compensation value based on the step of comparing; remeasuring the hardware dc offset error; comparing the remeasured hardware dc offset error to predetermined limits; determining signal strength conditions, if the dc offset error does not exceed the predetermined limits; under weak signal conditions, returning to the step of initiating the I/Q integration; and under strong signal conditions, resetting the DSP parameters and adjusting the integration factor, a, prior to returning to the step of integration; determining a cause for the hardware dc offset error, if the dc offset error does exceed the predetermined limits; executing a hardware dc offset correction based on the cause of the hardware dc offset error; returning to the step of determining whether the operating protocol is analog or digital when the cause of the hardware dc offset error is due to a channel or scan change; and resetting the DSP parameters, adjusting the integration factor and returning to the step of initiating I/Q integration, when the cause of the hardware dc offset error is not due to channel or scan change. - View Dependent Claims (11)
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Specification