Method and system for calibrating phases of comb teeth in comb signal with pilot tone and using calibrated comb teeth phases to measure a device under test

Patent metadata

Field	Value
Publication number	US-9810726-B2
Application number	US-201514848971-A
Country	US
Kind code	B2
Filing date	Sep 9, 2015
Priority date	Sep 9, 2015
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

A system and method sequentially measure phases of selected comb teeth of a comb signal using a local oscillator (LO) signal whose frequency and phase are changed for each sequential measurement, and adjust the measured phases to account for the change of phase in the LO signal from measurement of one selected comb tooth to the next to ascertain reference phase differences between the selected comb teeth. The measured phases of the selected comb teeth are adjusted by applying a phase offset determined from a first phase and a second phase of a pilot tone which are measured using the LO signal, respectively, before and after the frequency and phase of the LO signal change from measurement of one comb tooth to the next. The frequency of the pilot tone is maintained to be substantially the same when measuring the first phase and the second phase of the pilot tone.

First claim

The invention claimed is:

1. A method, comprising:
producing a pilot tone with a pilot tone generator;
receiving a comb signal having a plurality of comb teeth, wherein selected comb teeth among the plurality of comb teeth span a selected bandwidth of the comb signal;
sequentially converting the selected comb teeth to a first intermediate frequency (IF) signal in a first IF channel by mixing the comb signal with a local oscillator (LO) signal, wherein a frequency of the LO signal is changed for each sequential conversion such that for each frequency of the LO signal at least one of the selected comb teeth is converted to fall within the first IF channel, and sequentially measuring calibration phases of the converted selected comb teeth in the first IF channel using a first measurement device whose measurement bandwidth for any frequency of the LO signal is less than the selected bandwidth of the comb signal;
mixing the pilot tone with the LO signal to produce a converted pilot tone in a second IF channel,
during at least some of the sequential conversions,
measuring a first phase of the converted pilot tone with the converted pilot tone at a first frequency in the second IF channel prior to changing the frequency of the LO signal,
measuring a second phase of the converted pilot tone with the converted pilot tone at a second frequency in the second IF channel subsequent to changing the frequency of the LO signal, where the frequency of the pilot tone is maintained to be substantially the same in measuring the first phase of the converted pilot tone as in measuring the second phase of the converted pilot tone, and
after measuring the first and second phases of the converted pilot tone, and before changing the frequency of the LO signal again, changing the frequency of the pilot tone such that the converted pilot tone is at the first frequency in the second IF channel; and

ascertaining reference phase differences between the converted selected comb teeth using the measured calibration phases of the converted selected comb teeth and the measured first and second phases of the converted pilot tone.

2. The method of claim 1 , wherein a first IF bandwidth of the first IF channel is approximately the same as a second IF bandwidth of the second IF channel.

3. The method of claim 1 , wherein an amount by which the frequency of the LO signal is changed for each sequential conversion is about equal to a difference between adjacent comb teeth of the comb signal.

4. The method of claim 1 , wherein ascertaining reference phase differences between the converted selected comb teeth using the measured calibration phases of the converted selected comb teeth and the measured first and second phases of the pilot tone comprises:
for at least a current one of the sequential conversions, determining a phase adjustment as a difference between: (1) the first phase of the converted pilot tone with the converted pilot tone at the first frequency, as measured for the current one of the sequential conversions, and (2) the second phase of the converted pilot tone with the converted pilot tone at the second frequency, as measured for an immediately preceding one of the sequential conversions;
ascertaining a measured phase difference between the measured calibration phase of the converted selected comb tooth of the current one of the sequential conversions, and the measured calibration phase of the converted selected comb tooth of the immediately preceding one of the sequential conversions; and
applying the determined phase adjustment to the measured phase difference to obtain the reference phase difference between the converted selected comb tooth of the current one of the sequential conversions and the converted selected comb tooth of the immediately preceding one of the sequential conversions.

5. The method of claim 1 , wherein the comb signal is received from a repetitive pulse generator.

6. The method of claim 1 , further comprising:
receiving from a device under test (DUT) an output signal having an output signal spectrum;
sequentially converting portions of the output signal spectrum down to a second intermediate frequency (IF) signal in the second IF channel by mixing the output signal with the LO signal, wherein a frequency of the LO signal is changed for each sequential conversion of the portions of the output signal spectrum, and measuring an amplitude and phase of the second IF signal as a function of frequency for each of the sequentially converted portions of the output signal spectrum using a second measurement device whose measurement bandwidth for any frequency of the LO signal is less than a bandwidth of the output signal spectrum;
during at least some of the sequential conversions of the portions of the output signal spectrum, mixing the comb signal with the LO signal such that for each frequency of the LO signal at least the selected one of the comb teeth is converted to fall within the first IF channel, and sequentially measuring the phases of the converted selected comb teeth in the first IF channel using the first measurement device;
adjusting the measured phase of the second IF signal as a function of frequency for one or more of the sequentially converted portions of the output signal spectrum using the measured phases of the converted selected comb teeth and the reference phase differences between the converted selected comb teeth to produce phase-adjusted measurements of the second IF signal; and
stitching together the phase-adjusted measurements of the second IF signal to produce a measurement of the amplitude and phase of the output signal across the output signal spectrum as a function of frequency.

7. The method of claim 6 , wherein adjusting the measured phase of the second IF signal as a function of frequency for one or more of the sequentially converted portions of the output signal spectrum using the measured phases of the converted selected comb teeth and the reference phase differences between the converted selected comb teeth to produce phase-adjusted measurements of the second IF signal includes:
determining a phase difference between the measured phase of a converted selected comb tooth in the first IF channel in a current one of the sequential conversions of the portions of the output signal spectrum and the measured phase of a converted selected comb tooth in the first IF channel in a preceding one of the sequential conversions of the portions of the output signal spectrum to produce a measured comb tooth phase difference;
adjusting the measured comb tooth phase difference by applying a corresponding one of the reference phase differences to produce a phase adjustment for the second IF signal; and
applying the phase adjustment for the second IF signal to the measured phase of the second IF signal as a function of frequency to produce a phase-adjusted measurement of the second IF signal.

8. The method of claim 6 , further comprising:
receiving a second signal having a second signal spectrum;
during each sequential conversion of the portions of the second signal spectrum, sequentially converting portions of the second signal spectrum down to a third IF signal in a third IF channel by mixing the second signal with the LO signal, and measuring an amplitude and phase of the third IF signal as a function of frequency for each of the sequentially converted portions of the second signal spectrum using a third measurement device whose measurement bandwidth for any frequency of the LO signal is less than a bandwidth of the second signal spectrum;
adjusting the measured phase of the third IF signal as a function of frequency for one or more of the sequentially converted portions of the second signal spectrum using the measured phases of the co

Assignees

• Keysight Technologies Inc

Inventors

• Nielsen Troels Studsgaard
• Tafuri Felice Francesco

Classifications

• G01R25/00 Primary

  Arrangements for measuring phase angle between a voltage and a current or between voltages or currents · CPC title

• G01R35/007

  Standards or reference devices, e.g. voltage or resistance standards, "golden references" · CPC title

• H03L7/20

  using a harmonic phase-locked loop, i.e. a loop which can be locked to one of a number of harmonically related frequencies applied to it (H03L7/22 takes precedence) · CPC title