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Phase noise measurements utilizing a frequency down conversion/multiplier, direct spectrum measurement technique

  • US 5,337,014 A
  • Filed: 12/24/1992
  • Issued: 08/09/1994
  • Est. Priority Date: 06/21/1991
  • Status: Expired due to Term
First Claim
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1. A phase noise measuring circuit for measuring the noise a device under test, comprising:

  • a. a frequency mixer circuit, having a first input signal from a device under test and a second input signal from a reference stable oscillator having ultra low phase noise and a fixed center frequency, for mixing the first and second input signals to produce a down converted signal comprising the frequency difference signal of the first and second input signals;

    b. a down converted signal lowpass filter for passing the down converted signal;

    c. a frequency multiplier circuit, having the down converted signal as an input, for producing at its output a second harmonic signal, a fourth harmonic signal, an eighth harmonic signal, a sixteenth harmonic signal, and higher harmonic signals, of the down converted signal;

    d. a narrow bandpass filter, coupled to the output of said frequency multiplier circuit, for passing to its output one of the second harmonic, fourth harmonic, eighth harmonic, sixteenth harmonic, or higher harmonic, signals of the frequency multiplier circuit;

    e. an amplifier, coupled to the output of said narrow bandpass filter, for multiplying the output signal of the narrow bandpass filter and passing the amplified signal to its output; and

    f. a direct approach spectrum analyzer, connected directly to said amplifier output, for analyzing the output signal of said amplifier to measure the phase noise of the device under test.

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