Patents by Inventor David N. Critchlow

David N. Critchlow has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Patent number: 5842137
    Abstract: A subscriber unit for a wireless digital telephone system is disclosed. An equalizer for receiving I and Q samples is disclosed which is in the form. The I and Q samples are complex sample pairs provided at a frequency. The equalizer receives a training signal in the form of complex I and Q sample pairs. A training signal is affected by undesirable characteristics that might be present in the I and Q samples. A comparator compares the actual input training signal with the desired output to obtain a set of weighting coefficients for the equalizer to produce the desired output. A frequency correction circuit provides a corrected frequency signal for the frequency of the sample pairs from the weighting coefficients.
    Type: Grant
    Filed: June 22, 1994
    Date of Patent: November 24, 1998
    Assignee: InterDigital Technology Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 5659576
    Abstract: A device and method for receiving a radio signal transmitted over a channel, selecting and deselecting an equalizer, and balancing processing in response to such selection. A radio frequency signal is received from a transmission channel into a receive path, and delay spread in the radio frequency signal is estimated using an analysis circuit. The analysis circuit also determines a threshold delay spread. In the event the estimated delay spread exceeds the threshold delay spread, an equalizer is selected, otherwise the equalizer is deselected. Similarly, in the event the estimated delay spread does not exceed the threshold delay spread, a high complexity processor is selected, otherwise a low complexity processor is selected. If the low complexity processor is selected, an output signal is generated using the low complexity processor, and if the high complexity processor is selected, the output signal is generated using the high complexity processor.
    Type: Grant
    Filed: July 25, 1994
    Date of Patent: August 19, 1997
    Assignee: Hughes Electronics
    Inventors: David N. Critchlow, Michael Parr, Long Huynh
  • Patent number: 5325396
    Abstract: A subscriber unit for wireless communication with a base station in a wireless subscriber communication system includes a FIR chip, a DIF (digital intermediate frequency) chip, a single processor chip and a radio. The processor chip transcodes a digital voice input signal to provide digital input symbols; demodulates an output signal received from the base station to provide digital output symbols; and synthesizes a digital voice output signal from the digital output symbols. The FIR chip FIR filters the digital input symbols and generates timing signals for timing the transcoding and synthesizing operations in the processor chip. The DIF chip digitally synthesizes a digital intermediate frequency signal by direct digital synthesis (DDS) and modulates the digital intermediate frequency signal with the filtered input symbols to provide a modulated intermediate frequency input signal. The radio further processes the modulated input signal for transmission to the base station.
    Type: Grant
    Filed: September 4, 1992
    Date of Patent: June 28, 1994
    Assignee: InterDigital Technology Corporation
    Inventors: David N. Critchlow, Moshe Yehushua, Graham M. Avis, Wade L. Heimbigner, Karle J. Johnson, George A. Wiley
  • Patent number: 5311545
    Abstract: A receiver designed for use in a mobile environment, which includes an adaptive equalizer driven by phase estimation and rotation circuitry, and which is operable in multipath fading channels. The present invention uses an AFC loop and a phase rotation circuit in front of the adaptive equalizer to improve equalizer performance in the fading channel. The present invention uses .pi./4 phase rotation circuitry before a phase quantization decision is made. This .pi./4 phase rotation circuitry allows for decisions to be made on a QPSK constellation, rather than on an input 8PSK constellation, thus improving detection performance.
    Type: Grant
    Filed: June 17, 1991
    Date of Patent: May 10, 1994
    Assignee: Hughes Aircraft Company
    Inventor: David N. Critchlow
  • Patent number: 5282226
    Abstract: A mobile station cellular telephone transmitting system having a digital data source, waveform map, FIR filter with eight taps, a zero force circuit, start/end burst detection circuit, quadrature modulator, upconverter, and power amplifier. The ramping of the power output at the beginning and end of each frame slot or burst is controlled by forcing the first and last symbol of the burst's FIR filter output to zero.
    Type: Grant
    Filed: April 27, 1992
    Date of Patent: January 25, 1994
    Assignee: Hughes Aircraft Company
    Inventor: David N. Critchlow
  • Patent number: 5276706
    Abstract: A system and method for frequency acquisition by a mobile receiver 14 in a cellular communication system. Data for part of a frame 10 is sampled. Synchronization pattern 36 is rotated by a pattern rotator 37 to simulate fixed frequency offsets. The known sync pattern 36 is correlated with the sampled data by correlator 30 for a number of phase advances corresponding to the simulated fixed frequency offsets. The peak outputs 54 and 58 of the correlator 30 for the number of fixed frequency offsets is interpolated by parabolic interpolator 46 to adjust the receivers voltage controlled crystal oscillator 49 to reduce the offset.
    Type: Grant
    Filed: May 20, 1992
    Date of Patent: January 4, 1994
    Assignee: Hughes Aircraft Company
    Inventor: David N. Critchlow
  • Patent number: 5177741
    Abstract: In a wireless digital telephone system, a circuit for determining in a subscriber unit whether a particular RF channel is of the type designated by the base station to be either a control channel or a voice channel and for determining whether the channel is in the transmit or receive mode; the circuit utilizing the duration of an AM hole to determine the type of the channel and utilizing a unique word for determining the mode.
    Type: Grant
    Filed: October 12, 1988
    Date of Patent: January 5, 1993
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham N. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 5168507
    Abstract: A digital wireless subscriber telephone unit for wireless communication with a base station. An IF is used within the subscriber unit and base station which is combined with a carrier signal generated by a synthesizer for RF transmission between stations. In intervals between actuation of the system, a training mode is used wherein a known training signal is compared with a known values to produce correction coefficients to compensate for undesirable variations in timing and/or frequency, these constants being stored for use in correcting actual received signals. During demodulation, the modulated digital signals are fed to the modem processor in the form of time multiplexed I and Q samples and are demultiplexed. The demultiplexed I and Q samples are fed to an equalizer and frequency correction circuit for minimization of errors for production of a frequency correction signal based upon the correction coefficients which is used to correct any errors in the timing and frequency of the system.
    Type: Grant
    Filed: November 9, 1989
    Date of Patent: December 1, 1992
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 5159705
    Abstract: A frequency synthesizer that generates two output signals at a set frequency apart from each other and in synchronization with each other. The output frequency is selected by a microprocessor and the set frequency difference between the two output signals is determined by a frequency divider and a voltage controlled oscillator.
    Type: Grant
    Filed: March 13, 1992
    Date of Patent: October 27, 1992
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana
  • Patent number: 5146473
    Abstract: A subscriber unit for wireless communication with a base station in a wireless subscriber communication system includes a FIR chip, a DIF (digital intermediate frequency) chip, a single processor chip and a radio. The processor chip transcodes a digital voice input signal to provide digital input symbols; demodulates an output signal received from the base station to provide digital output symbols; and synthesizes a digital voice output signal from the digital output symbols. The FIR chip FIR filters the digital input symbols and generates timing signals for timing the transcoding and synthesizing operations in the processor chip. The DIF chip digitally synthesizes a digital intermediate frequency signal by direct digital synthesis (DDS) and modulates the digital intermediate frequency signal with the filtered input symbols to provide a modulated intermediate frequency input signal. The radio further processes the modulated input signal for transmission to the base station.
    Type: Grant
    Filed: February 20, 1991
    Date of Patent: September 8, 1992
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Moshe Yehushua, Graham M. Avis, Wade L. Heimbigner, Karle J. Johnson
  • Patent number: 5101418
    Abstract: A digital wireless subscriber telephone unit for wireless connection with a base station. The subscriber unit has a baseband processor which is coupled to a storage for the baseband functions. The baseband processor is direct access coupled to a modem processor whereby the two processors may communicate with each other. The modem processor generally acts as the master in the system, although lock-out device may be used in certain circumstances. The signal from the modem processor is converted to an analog signal, which is subjected to deglitching, and the deglitched signal is then upconverted and filted to form an IF signal which is thereafter amplified. The amplified IF signal is combined with a signal generated by a synthesizer to provide an RF signal. On the basis of certain signals received from the base station, the baseband processor produces initiating signals which determine whether the subscriber unit will be in the transmit mode or the receive mode.
    Type: Grant
    Filed: October 12, 1988
    Date of Patent: March 31, 1992
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 5067141
    Abstract: An interpolator varies the sampling rate of a signal. The signal may comprise pairs of in-phase and quadrature components at a first rate which are serially input through a pair of memories connected in series. The serially connected memories operate at a second higher rate which is a multiple of the first rate. An output taps the signals being circulated by the serially connected memories which results in the output of a signal having the in-phase and quadrature components at the higher second rate.
    Type: Grant
    Filed: October 10, 1989
    Date of Patent: November 19, 1991
    Assignee: International Mobile Machine Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 5008900
    Abstract: A subscriber unit for wireless communication with a base station in a wireless subscriber communication system includes a FIR chip, a DIF (digital intermediate frequency) chip, a single processor chip and a radio. The processor chip transcodes a digital voice input signal to provide digital input symbols; demodulates an output signal received from the base station to provide digital output symbols; and synthesizes a digital voice output signal from the digital output symbols. The FIR chip FIR filters the digital input symbols and generates timing signals for timing the transcoding and synthesizing operations in the processor chip. The DIF chip digitally synthesizes a digital intermediate frequency signal by direct digital synthesis (DDS) and modulates the digital intermediate frequency signal with the filtered input symbols to provide a modulated intermediate frequency input signal. The radio further processes the modulated input signal for transmission to the base station.
    Type: Grant
    Filed: August 14, 1989
    Date of Patent: April 16, 1991
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Moshe Yehushua, Graham M. Avis, Wade L. Heimbigner, Karle J. Johnson, George A. Wiley
  • Patent number: 4996697
    Abstract: In a digital wireless subscriber telephone unit for wireless connection with a base station which includes a modem processor whose signal is converted to an analog signal which is then upconverted and filtered to form an IF signal, a deglitching circuit for removing glitch spikes occurring during the transition periods from digital signals to analog signals comprising a timing system, a detector for detecting the transistion periods in order to control the timing system, and a mixer coupled to the output of a D/A converter to mix a blanking signal from the timing system with the analog signal received from the D/A converter during the transistion periods, whereby the output of the mixer is returned to an intermediate reference level.
    Type: Grant
    Filed: October 12, 1988
    Date of Patent: February 26, 1991
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 4994802
    Abstract: An analog to digital converter system utilizable in a wireless digital telephone network, the system comprising a circuit to produce an analog signal, and a circuit for amplifying this signal, mixing the amplified signal with a signal from a timing circuit and applying the output of the mixer to a sample and hold circuit; the output of the sample and hold circuit being then applied to an analog to digital converter, the output of which is applied to a FIFO, whose output is then available for further processing.
    Type: Grant
    Filed: October 12, 1988
    Date of Patent: February 19, 1991
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 4943983
    Abstract: A digital wireless subscriber telephone unit for wireless connection with a base station. The subscriber unit has a baseband processor which is coupled to storage means for the baseband functions. The baseband processor is direct access coupled to a modem processor whereby the two processors may communicate with each other. The modem processor generally acts as the master in the system, although lock-out means may be used in certain circumstances. The signal from the modem processor is converted to an analog signal, which is subjected to deglitching, and the deglitched signal is then upconverted and filtered to form an IF signal which is thereafter amplified. The amplified IF signal is combined with a signal generated by a synthesizer to provide an RF signal. On the basis of certain signals received from the base station, the baseband processor produces initiating signals which determines whether the subscriber unit will be in the transmit mode or the receive mode.
    Type: Grant
    Filed: October 12, 1988
    Date of Patent: July 24, 1990
    Assignee: International Mobile Machines Corporation
    Inventor: David N. Critchlow
  • Patent number: 4893317
    Abstract: A digital wireless subscriber telephone unit for wireless connection with a base station. The subscriber unit has a baseband processor which is coupled to storage device for the baseband functions. The baseband processor is direct access coupled to a modem processor whereby the two processors may communicate with each other. The modem processor generally acts as the master in the system, although lock-out circuit may be used in certain circumstances. The signal from the modem processor is converted to an analog signal, which is subjected to deglitching, and the deglitched signal is then upconverted and filtered to form an IF signal which is thereafter amplified. The amplified IF signal is combined with a signal generated by a synthesizer to provide an RF signal. On the basis of certain signals received from the base station, the baseband processor produces initiating signals which determine whether the subscriber unit will be in the transmit mode or the receive mode.
    Type: Grant
    Filed: October 12, 1988
    Date of Patent: January 9, 1990
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 4881240
    Abstract: A digital wireless subscriber telephone unit for wireless connection with a base station. The subscriber unit has a baseband processor which is coupled to storage device for the baseband functions. The baseband processor is direct access coupled to a modem processor whereby the two processors may communicate with each other. The modem processor generally acts as the master in the system, although lock-out circuit may be used in certain circumstances. The signal from the modem processor is converted to an analog signal, which is subjected to deglitching, and the deglitched signal is then upconverted and filtered to form an IF signal which is thereafter amplified. The amplified IF signal is combined with a signal generated by a synthesizer to provide an RF signal. On the basis of certain signals received from the base station, the baseband processor produces initiating signals which determine whether the subscriber unit will be in the transmit mode or the receive mode.
    Type: Grant
    Filed: October 12, 1988
    Date of Patent: November 14, 1989
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling, Eric Paneth, Moshe Yehushua
  • Patent number: 4825448
    Abstract: A digital wireless subscriber telephone unit for wireless connection with a base station. The subscriber unit has baseband processor which is coupled to storage means for the baseband functions. The baseband processor is direct access coupled to a modem processor whereby the two processors may communicate with each other. The modem processor generally acts as the master in the system, although lock-out means may be used in certain circumstances. The signal from the modem processor is converted to an analog signal, which is subjected to deglitching, and the deglitched signal is then upconverted and filtered to form an IF signal which is thereafter amplified. The amplified IF signal is combined with a signal generated by a synthesizer to provide an RF signal. On the basis of certain signals received from the base station, the baseband processor produces initiating signals which determine whether the subscriber unit will be in the transmit mode or the receive mode.
    Type: Grant
    Filed: August 7, 1986
    Date of Patent: April 25, 1989
    Assignee: International Mobile Machines Corporation
    Inventors: David N. Critchlow, Graham M. Avis, Sandra J. K. Earlam, Karle J. Johnson, Bruce A. Smetana, Gregory L. Westling
  • Patent number: 4764940
    Abstract: A modulator for a modem, said modulator being adapted to convert a bit stream, wherein each given number of successive bits defines a symbol, into a phase modulated intermediate frequency (IF) signal, the symbols in the modulator section being phase modulated DPSK conversion. The phase modulated symbols are then digitally filtered to provide a filtered signal comprising time shared, digital in-phase and quadrature phase components that, when converted into an analog signal, provides a modulation signal of a frequency that is centered about a predetermined frequency and deviates therefrom in accordance with the value of the phase modulated symbol. The filtered signal, after being converted to an analog signal is then filtered and passed to a mixer for up conversion to an IF signal.
    Type: Grant
    Filed: November 24, 1986
    Date of Patent: August 16, 1988
    Assignee: International Mobile Machines Corporation
    Inventors: Eric Paneth, David N. Critchlow, Moshe Yehushua