RF front-end with signal cancellation using receiver signal to eliminate duplexer for a cordless phone

Claim 2

An adaptive signal canceler for a radio-frequency (RF) front-end comprising: a composite-signal input for a composite signal from an antenna, the composite signal including a receiver signal received by the antenna and a transmitter signal transmitted by the antenna; an output, the output coupled to a receiver for amplifying the receiver signal, the output for outputting an output receiver signal generated from the composite signal with the transmitter signal substantially cancelled, leaving the receiver signal; a limiting circuit, coupled to receive the composite signal, for limiting an amplitude of the composite signal to generate a clipped signal having a constant amplitude; a synchronous detector, coupled to receive the clipped signal from the limiting circuit, and coupled to receive the output receiver signal, for generating an adjust signal; a canceling-signal generator, coupled to receive the clipped signal and controlled by the adjust signal, for generating a canceling signal from the clipped signal by adjusting a phase and an amplitude of the clipped signal in response to the adjust signal; and a signal combiner, coupled to receive the composite signal and the canceling signal, for combining the canceling signal with the composite signal to generate the output receiver signal, whereby the canceling signal is generated from the composite signal that includes both the transmitter signal and the receiver signal from the antenna.

Claim 3

The adaptive signal canceler of claim 1 wherein the synchronous detector includes a minimizer for generating the adjust signal so as to minimize a time-averaged amplitude of the output receiver signal, wherein the adaptive signal canceler operates to minimize the time-averaged amplitude of the output receiver signal; wherein the receiver signal is asynchronous to the transmitter signal, the receiver signal operating at a different frequency than the transmitter signal, wherein the receiver signal has a time-averaged amplitude of zero when sampled at a rate synchronized to the transmitter signal, whereby the adaptive signal canceler removes the transmitter signal from the composite signal by minimizing the time-averaged amplitude of the output receiver signal.

Claim 4

The adaptive signal canceler of claim 2 further comprising: an integrator, coupled to the adjust signal from the synchronous detector, for time-averaging changes in the adjust signal instantaneously detected by the synchronous detector, whereby the adjust signal is time-averaged.

Claim 5

The adaptive signal canceler of claim 3 wherein the integrator is a servo integrator that generates a larger adjust voltage of the adjust signal when a larger phase or amplitude difference between the clipped signal and the output receiver signal is detected, the larger adjust voltage causing the canceling-signal generator to more rapidly change the phase or amplitude of the canceling signal.

Claim 6

The adaptive signal canceler of claim 1 wherein the adjust signal comprises: a phase-adjust signal and an amplitude-adjust signal, the phase-adjust signal indicating an amount of phase adjustment needed for the clipped signal to match a phase of the transmitter signal, the amplitude-adjust signal indicating an amount of amplitude adjustment needed to match an amplitude of the transmitter signal in the composite signal.

Claim 7

The adaptive signal canceler of claim 5 wherein the limiting circuit further comprises: a feedback limiter, receiving the canceling signal from the canceling-signal generator, for generating a second clipped signal, the second clipped signal coupled to the synchronous detector for detecting an amplitude of the output receiver signal; and wherein the synchronous detector further comprises: a phase detector, for comparing phases of the clipped signal to the second clipped signal, and for generating a phase-adjust signal to the canceling-signal generator.

Claim 8

The adaptive signal canceler of claim 5 further comprising: a low-pass filter on the clipped signal, for removing higher-frequency harmonics of the receiver signal from the clipped signal.

Claim 9

The adaptive signal canceler of claim 1 wherein the adaptive signal canceler is not connected to a transmitter generating the transmitter signal, the adaptive signal canceler generating the canceling signal from the composite signal and not from an isolated transmitter signal without the receiver signal.

Claim 10

The adaptive signal canceler of claim 8 wherein impedance changes of the antenna occur when a person touches the antenna, the impedance changes altering the phase and amplitude of the transmitter signal in the composite signal, whereby the canceling signal is adapted to the impedance changes of the antenna by extracting the transmitter signal from the composite signal after the antenna, the canceling signal being adjusted in phase and amplitude independent of the impedance changes that alter the transmitter signal.

Claim 11

The adaptive signal canceler of claim 1 wherein the signal combiner comprises a difference amplifier, the canceling signal being an inverse of the transmitter signal extracted from the composite signal.

Claim 12

A cordless phone comprising: a common antenna for both transmitting a transmit signal and for receiving a receive signal; an antenna coupler connected to the common antenna, the antenna coupler having an input for the transmit signal and an output for a composite signal that includes both the receive signal and the transmit signal; a transmitter, coupled to accept and frequency-modulate an audio signal to generate at a radio-frequency the transmit signal, the transmitter sending the transmit signal to the common antenna through the input of the antenna coupler, the transmitter operating at a transmit frequency; a receiver, coupled to accept the composite signal from the common antenna through the output of the antenna coupler, for generating an audio input signal from a radio-frequency of the receive signal, the receiver operating at a receive frequency different from the transmit frequency; and a signal canceler, within the receiver, for extracting a modified transmit signal from the composite signal, the signal canceler subtracting the modified transmit signal from the composite signal to generate a recovered receive signal, the recovered receive signal being used by the receiver to generate the audio input signal, wherein the modified transmit signal is significantly larger than the receive signal wherein voltage extremes of the composite signal contain the receive signal superimposed on the transmit signal, and wherein the signal canceler further comprises: a difference amplifier, receiving the composite signal and a canceling signal, for outputting the recovered receive signal as a difference of the composite signal and the canceling signal; a first voltage limiter, receiving the composite signal, for removing the voltage extremes of the composite signal to generate a clipped signal; a second voltage limiter, receiving the canceling signal, for outputting a second clipped signal having phase information of the canceling signal; a phase comparator, coupled to the clipped signal and the second clipped signal, for outputting a phase-difference signal; a phase shifter, receiving the clipped signal, for advancing or retarding a phase of the clipped signal in response to the phase-difference signal, the phase-shifter outputting a phase-altered signal; a synchronous detector, coupled to the second clipped signal and coupled to the recovered receive signal from the difference amplifier, for detecting an average amplitude of the recovered receive signal, the average amplitude being an average over a transmit-signal period of the second clipped signal; and a gain-controlled amplifier, coupled to the synchronous detector and to the phase-altered signal from the phase shifter, for amplifying the phase-altered signal by a gain controlled by the average amplitude detected by the synchronous detector to generate the canceling signal, whereby the composite signal is clipped, phase-adjusted, and gain-adjusted to generate the canceling signal and whereby the recovered receive signal is generated from the composite signal from the common antenna by canceling the modified transmit signal extracted from the composite signal by the signal canceler.

Claim 13

A cordless phone comprising: a common antenna for both transmitting a transmit signal and for receiving a receive signal; an antenna coupler connected to the common antenna, the antenna coupler having an input for the transmit signal and an output for a composite signal that includes both the receive signal and the transmit signal; a transmitter, coupled to accept and frequency-modulate an audio signal to generate at a radio-frequency the transmit signal, the transmitter sending the transmit signal to the common antenna through the input of the antenna coupler, the transmitter operating at a transmit frequency; a receiver, coupled to accept the composite signal from the common antenna through the output of the antenna coupler, for generating an audio input signal from a radio-frequency of the receive signal, the receiver operating at a receive frequency different from the transmit frequency; and a signal canceler, within the receiver, for extracting a modified transmit signal from the composite signal, the signal canceler subtracting the modified transmit signal from the composite signal to generate a recovered receive signal, the recovered receive signal being used by the receiver to generate the audio input signal, wherein the modified transmit signal is significantly larger than the receive signal wherein voltage extremes of the composite signal contain the receive signal superimposed on the transmit signal, and wherein the signal canceler further comprises: a difference amplifier, receiving the composite signal and a canceling signal, for outputting the recovered receive signal as a difference of the composite signal and the canceling signal; a first voltage limiter, receiving the composite signal, for removing the voltage extremes of the composite signal to generate a clipped signal; a second voltage limiter, receiving the canceling signal, for outputting a second clipped signal having phase information of the canceling signal; a phase comparator, coupled to the clipped signal and the second clipped signal, for outputting a phase-difference signal; a phase shifter, receiving the clipped signal, for advancing or retarding a phase of the clipped signal in response to the phase-difference signal, the phase-shifter outputting a phase-altered signal; a synchronous detector, coupled to the second clipped signal and coupled to the recovered receive signal from the difference amplifier, for detecting an average amplitude of the recovered receive signal, the average amplitude being an average over a transmit-signal period of the second clipped signal; and a gain-controlled amplifier, coupled to the synchronous detector and to the phase-altered signal from the phase shifter, for amplifying the phase-altered signal by a gain controlled by the average amplitude detected by the synchronous detector to generate the canceling signal, whereby the composite signal is clipped, phase-adjusted, and gain-adjusted to generate the canceling signal and whereby the recovered receive signal is generated from the composite signal from the common antenna by canceling the modified transmit signal extracted from the composite signal by the signal canceler.

Claim 14

The cordless phone of claim 11 wherein the modified transmit signal is not exactly equivalent to the transmit signal from the transmitter, the common antenna and the antenna coupler modifying the transmit signal to generate the modified transmit signal, whereby the signal canceler subtracts the modified transmit signal from the composite signal, the signal canceler adapting to alterations of the transmit signal by the common antenna and the antenna coupler.

Claim 15

The cordless phone of claim 12 further comprising: pre-amplifier means, coupled between the antenna coupler and the signal canceler, for amplifying the composite signal from the antenna coupler.

Claim 16

The cordless phone of claim 11 wherein the antenna coupler is a ferrite-core coupler attenuating the transmit signal and the receive signal by about a same attenuation, whereby the antenna coupler provides an insignificant selectivity between the transmit and receive signals.

Claim 17

The cordless phone of claim 14 wherein a duplexer is eliminated from the antenna coupler.

Claim 18

The cordless phone of claim 14 wherein the common antenna is less than one-quarter of a wavelength of the transmit frequency, the common antenna being sensitive to handling by a person and altering phase or amplitude of the transmit signal coupled to the receiver.

Claim 19

The cordless phone of claim 11 wherein the transmit frequency and the receive frequency are near 49 MHz.

Claim 20

A signal canceler for a cordless telephone receiver comprising: combiner means, receiving a composite signal that includes a transmit signal and a receive signal, the combiner means also receiving a canceling signal, for outputting a recovered receive signal as a difference or sum of the composite signal and the canceling signal; first voltage limiter means, receiving the composite signal, for removing voltage extremes of the composite signal to generate a clipped signal; phase comparator means, coupled to the clipped signal, for outputting a phase-difference signal indicating a phase difference between the clipped signal and the canceling signal; phase shift means, receiving the clipped signal, for adjusting a phase of the clipped signal in response to the phase-difference signal, the phase-shifter outputting a phase-altered signal; synchronous detect means, coupled to the recovered receive signal, for detecting an average of the recovered receive signal, the average being an average over a transmit-signal period; and gain-control means, coupled to the synchronous detect means and to the phase-altered signal from the phase shifter, for amplifying or attenuating the phase-altered signal by a gain that is controlled by the average detected by the synchronous detect means to generate the canceling signal, whereby the composite signal is clipped, phase-adjusted, and gain-adjusted to generate the canceling signal.

Claim 21

A signal canceler for a cordless telephone receiver comprising: combiner means, receiving a composite signal that includes a transmit signal and a receive signal, the combiner means also receiving a canceling signal, for outputting a recovered receive signal as a difference or sum of the composite signal and the canceling signal; first voltage limiter means, receiving the composite signal, for removing voltage extremes of the composite signal to generate a clipped signal; phase comparator means, coupled to the clipped signal, for outputting a phase-difference signal indicating a phase difference between the clipped signal and the canceling signal; phase shift means, receiving the clipped signal, for adjusting a phase of the clipped signal in response to the phase-difference signal, the phase-shifter outputting a phase-altered signal; synchronous detect means, coupled to the recovered receive signal, for detecting an average of the recovered receive signal, the average being an average over a transmit-signal period; and gain-control means, coupled to the synchronous detect means and to the phase-altered signal from the phase shifter, for amplifying or attenuating the phase-altered signal by a gain that is controlled by the average detected by the synchronous detect means to generate the canceling signal, whereby the composite signal is clipped, phase-adjusted, and gain-adjusted to generate the canceling signal.