Apparatus and methods for eliminating DC offset in a wireless communication device
First Claim
1. An amplifier system for amplifying signals having frequencies above a second frequency, the amplifier system having a frequency dependent direct current (DC) offset canceling system, comprising:
- a forward amplifier having a forward amplifier gain and providing a system output;
a feedback amplifier having an input coupled to the system output and having a feedback amplifier gain, wherein the product of said forward amplifier gain and said feedback amplifier gain is larger than one below a first frequency and substantially less than one above the second frequency, the second frequency being higher than the first frequency; and
, a summing unit coupled to combine an input signal and a feedback signal from said feedback amplifier, and providing the combined signal as an input to said forward amplifier.
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Abstract
Apparatus and methods for eliminating DC offset in a wireless communication device operable on a continuous basis or on a sampled basis. In a receive channel, the output of a forward variable gain amplifier is fed back to an RC circuit to charge the capacitor (C) to a voltage dependent on the DC offset in the variable gain amplifier output. The voltage on the capacitor is amplified and summed with the input to the variable gain amplifier. The RC circuit is configured to provide a high gain feedback at DC and very low frequencies, but very low gain at signal frequencies. Preferably the output of the forward variable gain amplifier is fed back to the RC circuit with a gain that is inversely proportional to the forward gain. Disconnection of the capacitor and feedback of the capacitor voltage provides sampled operation. Various embellishments and sample applications are disclosed.
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Citations
32 Claims
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1. An amplifier system for amplifying signals having frequencies above a second frequency, the amplifier system having a frequency dependent direct current (DC) offset canceling system, comprising:
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a forward amplifier having a forward amplifier gain and providing a system output;
a feedback amplifier having an input coupled to the system output and having a feedback amplifier gain, wherein the product of said forward amplifier gain and said feedback amplifier gain is larger than one below a first frequency and substantially less than one above the second frequency, the second frequency being higher than the first frequency; and
, a summing unit coupled to combine an input signal and a feedback signal from said feedback amplifier, and providing the combined signal as an input to said forward amplifier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A wireless receiver comprising:
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a low-noise amplifier having an input coupled to an antenna output;
a mixer coupled to receive a signal from said low-noise amplifier, said mixer being capable of mixing said signal from said low-noise amplifier with a local oscillator frequency and providing a mixer output signal;
a forward amplifier coupled to receive said mixer output signal and providing a receiver output signal, the forward amplifier having a forward amplifier gain;
a feedback amplifier coupled to receive an output from said forward amplifier and having a feedback amplifier gain, the magnitude of the product of said forward amplifier gain and said feedback amplifier gain being larger than one below a first frequency and substantially less than one above a second frequency higher than the first frequency; and
,a summing unit for combining said mixer output signal and a feedback signal from said feedback amplifier, and providing the combined signal as an input to said forward amplifier. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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Specification