Methods and apparatus for calibrating oscillators in a receiver
First Claim
1. A receiver, comprising:
- a reference signal generator comprising a first oscillator supplying a reference frequency signal, the reference signal generator producing both a first frequency conversion signal and a local calibration signal from the reference frequency signal, wherein the local calibration signal is generated from a harmonic of the reference frequency signal;
a first frequency converter responsive to the first frequency conversion signal to down-convert a frequency of a received signal during normal receive operation and to down-convert a frequency of the local calibration signal from the reference signal generator using the first frequency conversion signal from the reference signal generator during calibration processing;
a first switch in a path between an antenna and the receiver;
a second switch in a path between the reference signal generator and the first frequency converter, wherein the first switch is closed and the second switch is open during normal receive operation such that the received signal is supplied to the first frequency converter, and the first switch is open and the second switch is closed during calibration processing such that the local calibration signal is supplied to the first frequency converter;
a second oscillator having a lower accuracy than the first oscillator, the second oscillator generating a second frequency conversion signal;
a second frequency converter responsive to the second frequency conversion signal to further down-convert the frequency of the received signal during normal receive operation and to further down-convert the frequency of the local calibration signal during calibration processing;
a demodulator configured to demodulate the received signal at a demodulation frequency during normal receive operation; and
a frequency error processor configured to determine a frequency error from the local calibration signal at the demodulation frequency during calibration processing, wherein the reference signal generator adjusts a frequency of the first frequency conversion signal used during normal receive operation in response to the frequency error to compensate for the frequency error, wherein adjusting the frequency of the first frequency conversion signal compensates for frequency errors introduced by the second oscillator.
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Abstract
A receiver includes a first oscillator supplying a reference frequency signal; a reference signal generator producing a first frequency conversion signal and a local calibration signal from the reference frequency signal; a first frequency converter responsive to the first frequency conversion signal to down-convert the received signal during normal receive operation and to down-convert the local calibration signal during calibration processing; a second frequency converter responsive to a second frequency conversion signal from a second oscillator to further down-convert the received signal and the local calibration signal; a demodulator that demodulates the received signal at a demodulation frequency; and a frequency error processor that determines a frequency error from the local calibration signal at the demodulation frequency, wherein the reference signal generator adjusts a frequency of the first frequency conversion signal used during normal receive operation in response to the frequency error to compensate for the frequency error.
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Citations
27 Claims
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1. A receiver, comprising:
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a reference signal generator comprising a first oscillator supplying a reference frequency signal, the reference signal generator producing both a first frequency conversion signal and a local calibration signal from the reference frequency signal, wherein the local calibration signal is generated from a harmonic of the reference frequency signal; a first frequency converter responsive to the first frequency conversion signal to down-convert a frequency of a received signal during normal receive operation and to down-convert a frequency of the local calibration signal from the reference signal generator using the first frequency conversion signal from the reference signal generator during calibration processing; a first switch in a path between an antenna and the receiver; a second switch in a path between the reference signal generator and the first frequency converter, wherein the first switch is closed and the second switch is open during normal receive operation such that the received signal is supplied to the first frequency converter, and the first switch is open and the second switch is closed during calibration processing such that the local calibration signal is supplied to the first frequency converter; a second oscillator having a lower accuracy than the first oscillator, the second oscillator generating a second frequency conversion signal; a second frequency converter responsive to the second frequency conversion signal to further down-convert the frequency of the received signal during normal receive operation and to further down-convert the frequency of the local calibration signal during calibration processing; a demodulator configured to demodulate the received signal at a demodulation frequency during normal receive operation; and a frequency error processor configured to determine a frequency error from the local calibration signal at the demodulation frequency during calibration processing, wherein the reference signal generator adjusts a frequency of the first frequency conversion signal used during normal receive operation in response to the frequency error to compensate for the frequency error, wherein adjusting the frequency of the first frequency conversion signal compensates for frequency errors introduced by the second oscillator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 18)
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16. In a receiver employing a reference oscillator and a lower accuracy oscillator, a method for calibrating oscillator frequency to compensate for a frequency error caused by the lower accuracy oscillator, comprising:
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(a) isolating the receiver from external signals by opening a first switch between an antenna and the receiver during calibration processing; (b) generating a local calibration signal from a harmonic of a reference frequency signal supplied by the reference oscillator and supplying the local calibration signal to the receiver via a path including a second switch that is closed during calibration processing; (c) down-converting the frequency of the local calibration signal generated from the reference frequency signal using a first frequency conversion signal also generated from the reference frequency signal; (d) further down-converting the frequency of the local calibration signal in accordance with a second frequency conversion signal generated by the lower accuracy oscillator; (e) measuring the frequency error from the local calibration signal at a demodulation frequency; and (f) adjusting a frequency of the first frequency conversion signal used for subsequent reception of external signals to compensate for the frequency error caused by the lower accuracy oscillator. - View Dependent Claims (17, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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Specification