Direct current offset cancellation for mobile station modems using direct conversion
First Claim
1. A DC offset cancellation block in an RF receiver having a direct converter for direct down conversion of a received RF signal to a baseband signal, said DC offset cancellation block comprising:
- offset adjustment means for removing static DC components from said baseband signal;
a coarse-grain loop for removing large portions of said static DC components and time-varying DC components from said baseband signal;
a fine-grain loop for removing said static and said time varying DC components from said baseband signal; and
a digital-to-analog converter controller (DACC) for removing large portions of said static DC components and slowly time-varying DC components by means of updating a digital-to-analog converter in said direct converter with a DC offset based on gain setting, receive frequency changes, and temperature changes of a low noise amplifier (LNA), a mixer, a baseband filter and an analog-to-digital converter (ADC) from a front end of said RF receiver;
wherein said offset adjustment means, said coarse-grain loop, said fine-grain loop, and said DACC interact with one another to remove unwanted DC offsets in said RF receiver.
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Accused Products
Abstract
A system and method for canceling DC offset for Mobile Station Modems having direct conversion architectures. The present invention is a fast acquiring DC offset cancellation block that provides rapid and accurate DC offset estimates and cancellation techniques to support direct conversion architectures. The fast acquiring DC offset cancellation block combines four mechanisms to rapidly acquire and remove a DC offset estimate after power up, temperature changes, receiver frequency changes, and gain setting changes by increasing high pass loop bandwidth and adjusting DC offset levels at baseband. After removing the DC offset in large portions, the high pass loop bandwidth is decreased to fine tune the previous estimate and to remove any small variation in DC offset due to receiver self-mixing products.
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Citations
23 Claims
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1. A DC offset cancellation block in an RF receiver having a direct converter for direct down conversion of a received RF signal to a baseband signal, said DC offset cancellation block comprising:
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offset adjustment means for removing static DC components from said baseband signal; a coarse-grain loop for removing large portions of said static DC components and time-varying DC components from said baseband signal; a fine-grain loop for removing said static and said time varying DC components from said baseband signal; and a digital-to-analog converter controller (DACC) for removing large portions of said static DC components and slowly time-varying DC components by means of updating a digital-to-analog converter in said direct converter with a DC offset based on gain setting, receive frequency changes, and temperature changes of a low noise amplifier (LNA), a mixer, a baseband filter and an analog-to-digital converter (ADC) from a front end of said RF receiver; wherein said offset adjustment means, said coarse-grain loop, said fine-grain loop, and said DACC interact with one another to remove unwanted DC offsets in said RF receiver. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for cancelling DC offset in an RF receiver having a direct converter for direct down conversion of a received RF signal to a baseband signal, said method comprising the steps of:
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(1) applying a high gain to expand the bandwidth of a high pass filter when a gain change occurs in said RF receiver; (2) rapidly acquiring the DC offset within said baseband signal prior to the timing out of a timer; (3) applying a low gain to narrow the bandwidth of said high pass filter when the timer has timed-out; and (4) tracking the DC offset to fine tune the acquired DC offset, wherein the DC offset is removed from the baseband signal. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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22. A DC offset cancellation block;
- comprising;
offset adjustment means for removing static DC components from a baseband signal; a coarse-grain loop for removing large portions of said static DC components and time-varying DC components from said baseband signal; a fine-grain loop fur removing said static and time-varying DC components from said baseband signal; and a digital-to-analog converter controller (DACC) for removing large portions of said static DC components and slowly time-varying DC components by means of updating a digital-to-analog converter with a DC offset based on gain setting changes, frequency changes, and temperature changes of an amplifier and a mixer from a front end of a receiver. - View Dependent Claims (23)
- comprising;
Specification