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Direct conversion receiver with reduced even order distortion
| Details |
Inventors: Vagher, Michael R.;
Assignee: Rockwell Science Center, Inc. (Thousand Oaks, CA)
Primary Examiner: Bost; Dwayne D.
Assistant Examiner: Gantt; Alan T.
Attorney, Agent or Firm: Eppele; Kyle, O'Shaughnessy; James P.
A mixer for use in a direct conversion receiver includes a compensating differential amplifier which injects equal amplitude opposite phase currents with respect to even order distortion currents. The compensating differential amplifier utilizes an ideal current source. The mixer is an active mixer which utilizes four switching transistors. The even order distortion is introduced by non-linear components which demonstrate strong off-channel signals. |
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DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS In FIG.
1, a direct conversion receiver (DCR) system 10 includes an antenna 12, a band-pass filter 14, a mixer or conversion circuit 20, a low-pass filter 16, and a digital signal processor 18.
Radio frequency (RF) signals are received on antenna 12 and provided through a band-pass filter 14 to an input 22 of circuit 20.
The RF signals are preferably modulated high frequency signals and can be ultra-high frequency (UHF), very-high frequency (VHF), or other frequency signals.
System 10 can be utilized in a variety of communication applications, including aircraft radio receivers.
Circuit 20 utilizes an oscillator signal to convert the RF signal at input 22.
The oscillator signal can be produced by any frequency source, such as, a voltage controlled oscillator, a direct digital synthesizer, a divider or other high frequency signal source.
The oscillator signal can be in the UHF, VHF or other frequency range.
Circuit 20 provides a mixed or composite signal comprised of the local oscillator frequency, the carrier frequency of the RF signal, the local oscillator frequency plus the carrier frequency and the baseband signal.
The baseband signal represents the modulation on the RF signal.
Filter 16 is preferably a low-pass filter which separates or filters out the higher frequency signals from the composite signal leaving only the baseband signal.
The baseband signal is provided to processor 18 for further operations in the system 10.
Conversion circuit 20 is optimized to reduce even order distortion present in the composite signal.
Conversion circuit 20 preferably includes a cancellation or compensation circuit (not shown in FIG.
1) which injects a feedback signal 180 degrees out-of-phase from the even order distortion to reduce the even order distortion in the composite signal.
The even order distortion can typically be represented by second order distortion which is usually the largest component of even order distortion.
The even order distortion is generally introduced by non-linear components in circuit 20 which demodulate strong off-channel signals independently of the oscillator frequency
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