Method and apparatus for improved zero intermediate frequency receiver latency

• US 5,901,344 A
• Filed: 09/09/1997
• Issued: 05/04/1999
• Est. Priority Date: 12/19/1995
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Opas, George Francis
• Primary Examiner(s): VO, NGUYEN THANH
• Application Number:
  US08/926,180
• Time in Patent Office: 602 Days
• Field of Search: 455/73, 455/76, 455/78, 455/82, 455/83, 455/84, 455/86, 455/324, 455/255
• US Class Current: 455/76
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04B 1/40 Circuits

Abstract

A transceiver (10) in a first embodiment includes a zero intermediate frequency (ZIF) receiver (11), which achieves high throughput operation by reducing receiver latency time due to receiver response within a receiver pass band to carrier spectral components of a modulated carrier frequency. During a receive mode, a receiver local oscillator (LO) frequency is offset from the carrier frequency within the receiver pass band, preferably as determined by worst case errors in the carrier frequency and the LO frequency. During a transmit mode, the receiver LO frequency is modulated in such a way as to suppress the LO center frequency component in the modulated spectrum.

Claims

1. A single frequency duplex transceiver comprising:

a zero intermediate frequency (ZIF) receiver having a receiver bandwidth and a first input for receiving a receiver carrier frequency having an associated carrier frequency error during a receive mode of the transceiver;

a receiver local oscillator source having a modulation input for receiving a modulating signal to modulate a receive local oscillator frequency during a transmit mode and an output which couples the local oscillator frequency to a second input of the ZIF receiver;

a transmit carrier source providing a transmit carrier output frequency; and

a transceiver reference source providing a first reference signal from a first reference output coupled to a reference input to the receiver local oscillator source, and providing a second reference signal from a second reference output coupled to a reference input to the transmit carrier source;

wherein the transceiver reference source is operable for providing the second reference signal having a same reference frequency as the first reference signal, and wherein the transmit carrier output frequency and the receiver carrier frequency are substantially the same allowing said transceiver to have substantially the same transmit and receive frequencies.

2. The transceiver of claim 1 wherein the transmit carrier output frequency is synthesized using the second reference signal as a reference.

3. The transceiver of claim 1, wherein the local oscillator source is adapted for receiving the modulating signal when the modulating signal has a constant level during the receive mode and a substantially symmetrical square wave characteristic having maximum and minimum values with an average value equal to the constant level during the transmit mode.

4. A method of reducing receiver latency time due to receiver response within a receiver bandwidth to carrier spectral components of a modulated carrier frequency, comprising the step of:

in a single frequency duplex transceiver having a zero intermediate frequency receiver, modulating a receive local oscillator frequency in response to a modulating waveform in a transmit mode;

providing a transmit carrier output frequency of the same frequency of said modulated carrier frequency; and

providing a first and second reference signals of a same reference frequency for synthesizing said transmit carrier output frequency and said receive local oscillator frequency allowing said transceiver to have substantially the same transmit and receive frequencies.

5. The method of claim 4, wherein the step of modulating the receive local oscillator frequency includes applying the modulating waveform to modulate the receive local oscillator frequency such that a center frequency component of a receive local oscillator is nulled.

6. The method of claim 5 wherein modulating the receive local oscillator frequency includes using a periodic symmetrical square wave for the modulating waveform to reduce a level of down-converted modulated transmitter carrier spectral components that occur at about zero Hertz.