DC offset cancellation circuits and methods
First Claim
1. A wireless receiver comprising:
- a mixer having a first input, a second input and an output, wherein the first input is coupled to a first amplifier to receive an amplified RF signal and the second input is coupled to a frequency synthesizer to receive a first signal having one of a plurality of frequencies; and
a plurality of parallel DC offset cancellation stages selectively coupled to the mixer output, wherein if the first signal has a first frequency, then a first one of the plurality of parallel DC offset cancellation stages is coupled to the mixer output, and if the first signal has a second frequency, then a second one of the plurality of parallel DC offset cancellation stages is coupled to the mixer output.
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Accused Products
Abstract
Embodiments of the present invention include circuits and methods for reducing DC Offset. In one embodiment the present invention includes storing DC offset on internal capacitances. In one embodiment, parallel stages are used to remove DC offset corresponding to different local oscillator frequencies. Embodiments of the invention further include changing the low cutoff frequency of the DC cancellation circuits for fast calibration. In a first state, a high pass filter may have a first low cutoff frequency, and in a second state the high pass filter may have a second cutoff frequency lower than the first low cutoff frequency. The present invention also includes a variable gain amplifier with reduced DC offset.
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Citations
20 Claims
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1. A wireless receiver comprising:
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a mixer having a first input, a second input and an output, wherein the first input is coupled to a first amplifier to receive an amplified RF signal and the second input is coupled to a frequency synthesizer to receive a first signal having one of a plurality of frequencies; and
a plurality of parallel DC offset cancellation stages selectively coupled to the mixer output, wherein if the first signal has a first frequency, then a first one of the plurality of parallel DC offset cancellation stages is coupled to the mixer output, and if the first signal has a second frequency, then a second one of the plurality of parallel DC offset cancellation stages is coupled to the mixer output. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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- 11. A wireless receiver comprising a first DC offset cancellation circuit, wherein in a first state, the first DC offset cancellation circuit has a first low cutoff frequency, and in a second state, the first DC offset cancellation circuit has a second low cutoff frequency less than the first low cutoff frequency.
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16. A wireless receiver including a DC offset cancellation circuit, the DC offset cancellation circuit comprising:
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a capacitor having a first terminal coupled to receive an input signal and a second terminal;
a first MOS transistor having a first terminal and a second terminal, the first terminal of the MOS transistor being coupled to the second terminal of the capacitor; and
a resistance coupled between the second terminal of the first MOS transistor and a reference voltage, wherein, in a first state, the resistance has a first value so that the circuit has a first low cutoff frequency, and in a second state, the resistance has a second value so that the circuit has a second low cutoff frequency less than the first low cutoff frequency. - View Dependent Claims (17, 18, 19, 20)
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Specification