Test method for frequency converters with embedded local oscillators
View Patent ↗A method is presented where the phase trace is offset for each sweep such that the first point is always at zero degrees. The resulting traces are then averaged. The average reduces the noise in the phase trace and results in a less noisy group delay trace.
1. A method of measuring a response of a frequency converter, the method comprising:
for a vector network analyzer with a reference mixer of a receiver in one channel and a mixer of a device under test (DUT) in another channel, each mixer having a local oscillator;
measuring a response of a ratio of an output signal of the DUT mixer to an output signal of the reference mixer;
computing a phase response from the ratio of the output signal of the DUT mixer and the output signal of the reference mixer;
normalizing the phase response by a phase of a predetermined point in the phase response; and
averaging several traces of the phase response.
2. A method as in claim 1 , further comprising determining a frequency of the local oscillator of the DUT mixer.
3. A method as in claim 2 further comprising offsetting the local oscillator of the reference mixer to match a frequency of the local oscillator of the DUT mixer.
4. A method as in claim 3 further comprising offsetting the receiver in frequency to match the output signal of the DUT mixer.
5. A method, as in claim 3 , wherein offsetting the local oscillator of the reference mixer to match a frequency of the local oscillator of the DUT mixer comprises determining the frequency of the local oscillator of the DUT mixer.
6. A method as in claim 1 wherein the response of the ratio of the output signal of the DUT mixer and the output signal of the reference mixer is one of a phase and group delay response.
7. A method, as in claim 1 , comprising:
setting one of a source and the receiver to a fixed frequency;
sweeping the other of the source and the receiver; and
measuring a peak value of an amplitude to determine an IF frequency.
8. A method, comprising:
for a network analyzer;
determining a frequency of a local oscillator within a device under test (DUT) mixer by measuring with the network analyzer an IF frequency output by the DUT;
offsetting one of a source and a receiver frequency used by a reference channel of the network analyzer to accommodate offsets in the local oscillator within the DUT mixer with respect to the source; and
measuring a response of the DUT mixer.
9. A method as in claim 8 , wherein determining the frequency of the local oscillator within the DUT mixer comprises applying a frequency sweep to the DUT mixer.
10. A method as in claim 8 , wherein determining the frequency of the local oscillator within the DUT mixer comprises applying a phase versus time sweep.
11. A method as in claim 8 , wherein measuring the response of the DUT mixer comprises measuring a phase response, and further comprises normalizing the phase response by the phase at a predetermined point in the phase response.
12. A method as in claim 11 , wherein measuring the response of the DUT mixer further comprises averaging the phase response.
13. A method for determining a frequency of an unknown signal, the method comprising:
applying the unknown signal to one channel of a vector network analyzer;
applying a signal of known frequency to another channel of the vector network analyzer;
measuring a phase versus time response of a ratio of the unknown signal and the signal of known frequency; and
determining a frequency offset between the unknown signal and the signal of known frequency based on a change of phase versus a change in time.
14. A method as in claim 13 wherein:
the unknown signal is an output of a mixer of a device under test; and
the known signal is an output of a mixer of a reference channel.