avoiding mixer compression when acting as a phase detector - Page 1
Forum section: electronics / projects

author: john23
author_rank: Frequent Contributor
timestamp: June 11, 2025, 12:20:18 pm
content: Hello,I need to make my M1-0616 mixer in a phase detector, so phase difference between RF and Lo will be transformed into phase detector.However there is a certain dinamic range for the mixer in which it can act as a phase detector as shown below.The IF port acts by transforming the phase difference of LO and RF into IF?My LO input power is 10dB, accroding to the the table.What is the allowed RF input power allowed so the mixer wont get compressed?What is the RF and LO power law for good phase detection between them?If I put 10dBm on RF and LO then I am afraid the mixer will be compressed.How to configure RF and LO ports properly for this purpose?Thanks.https://markimicrowave.com/products/connectorized/mixers/m1-0616mp/datasheet/

author: ftg
author_rank: Frequent Contributor
timestamp: June 11, 2025, 02:02:07 pm
content: But by compressing the mixer you get that nice linear slope for the phase.And also reduce amplitude variations in the IF / phase detector output.As for the correct RF power, in the past +10dBm was fine, at least for the mixers where that was below the absolute maximums.

author: john23
author_rank: Frequent Contributor
timestamp: June 11, 2025, 05:07:48 pm
content: Hello,This is a real eye opener , So you reccomend to compress in order to get a linear slope?Why is that?is there some theory or a link where I could read about it?Thanks.But by compressing the mixer you get that nice linear slope for the phase.And also reduce amplitude variations in the IF / phase detector output.

author: KE5FX
author_rank: Super Contributor
timestamp: June 11, 2025, 05:29:53 pm
content: A bit of compression (not enough to damage or overheat the diodes) is not a bad thing when using a mixer as a phase detector. The only really important thing is the phase angle. The mixer acts as a phase detector when the inputs are in quadrature, and it acts as an AM detector when the inputs are in phase.Compression has the effect of changing the Kphi gain, and you can assess that by looking at the IF waveform. But that's really all.

author: john23
author_rank: Frequent Contributor
timestamp: June 11, 2025, 09:16:08 pm
content: Hello ,I am trying to understand the sentence below.Phase detector is converting the phase different between LO and RF into voltage at IF , so when the phase difference is 90 degrees its only one point on the plot, how its a phase detector?"The mixer acts as a phase detector when the inputs are in quadrature"

author: TimFox
author_rank: Super Contributor
timestamp: June 11, 2025, 10:01:58 pm
content: To operate as a normal mixer, the LO power is sufficient to saturate the diodes, but the RF power is much lower. Then, the IF output is linear in the RF input, but almost independent of the LO power.If the mixer drive on both RF and LO is sufficient to drive the diodes into full conduction, the result is equivalent to multiplying two square waves.A digital circuit that does the same thing is to apply both coherent square waves to an XOR (exclusive-or) gate and average the output to get a linear dependence of voltage on phase difference.Diagrams:https://people.engr.tamu.edu/spalermo/ecen620/lecture04_ee620_phase_detectors.pdf

author: KE5FX
author_rank: Super Contributor
timestamp: June 11, 2025, 11:11:45 pm
content: Quote from: john23 on June 11, 2025, 09:16:08 pmYou're measuring the deviation from 90 degrees. That's the point where the phase-to-voltage conversion gain is at its highest, and also where the IF output is at zero volts.As the phase angles change, the voltage at the IF output goes up or down from there (maximum positive voltage at 0 degrees where the waveforms are coincident and the mixer is basically squaring the voltage, maximum negative voltage at 180 degrees where a positive RF voltage is always multiplied by a negative LO voltage and vice versa.)

author: john23
author_rank: Frequent Contributor
timestamp: June 12, 2025, 11:20:33 am
content: Hello , Thank you very much for the responce.my LO port is 10dBm my RF is 0dbM .When I start tuning one phase shifter then the voltage of the IF port goes from 0.3V to -0.3V.The question is does it a linear slope? I only have an ausiloscope to test the IF port voltage.Is there a way to test if my slope is linear?Thanks.https://technionmail-my.sharepoint.com/:u:/g/personal/yefimv_technion_ac_il/ETHaHNDGd9hFgUueAG2vXoUBcsuT5TswScVQ6tWTjGJO5A?e=sAlthEhttps://technionmail-my.sharepoint.com/:u:/g/personal/yefimv_technion_ac_il/EUyNT1LgdvRIngfrwPrAjYMBzR5k9Ls0IrQwe8hyNpspdA?e=y3Hgcehttps://technionmail-my.sharepoint.com/:v:/g/personal/yefimv_technion_ac_il/EXiJuopdTJVEofg3wWnqH_wBEDSQ1PivUIn0Fv_D1ZxtTw?e=N06ldU

author: IconicPCB
author_rank: Super Contributor
timestamp: June 12, 2025, 12:24:51 pm
content: An airline would be a good way to test it.Otherwise coaxial cable cut to specific length(s) in absence of an airline.the other option is given a fixed length coax line varybthefrequency and measure phase signal.Given a fixed length calculate phase delay at various frequencies and draw the conclusion.

author: erikka
author_rank: Regular Contributor
timestamp: June 12, 2025, 05:16:01 pm
content: The slope is linear when the output voltage does not change when either the LO or RF input power changesThe slope is linear because the output of two square waves multiplied is linear with the overlap

author: TimFox
author_rank: Super Contributor
timestamp: June 12, 2025, 05:23:51 pm
content: Back to the original question:When used as a mixer, the DBM operating conditions should avoid compression (of the RF input) to get a proper IF output.When used as a phase detector, the operating conditions shouldmaximizecompression, so that the IF output depends only on the phase difference, and is independent of variations in the RF or LO input level.

author: john23
author_rank: Frequent Contributor
timestamp: June 13, 2025, 08:33:46 am
content: Hello , currently my LO=10dBm and RF port is 0dBm.I have plugged the IF port into an osciloscope and saw that the phase shifter varies the IF output from -0.3 till 0.3.We want the IF not to be dependant on RF amplitude, so i will put 6 or 8 dBM at the PORT and IF will not change.Only when I change the phase shifter then I will see the IF change , correct?Thanks.

author: john23
author_rank: Frequent Contributor
timestamp: June 15, 2025, 05:48:07 am
content: Hello ,suppose In the current situation I just want basic lock and I will handle 1/f noise after I have basic lock.I want to plug circulator PORT C straight into mixer RF port.As you can see in the diagram below I have a DBM mixer shown in the link which acts as a phase detector.I was told to compress it so the IF port voldate DC amplitude will depend purely on the phase difference.However as you can see as we go closer and closer to the cavity resonator the amplitude from port C will get smaller and smaller .There will be at least 20dB difference between the center of the resonance and 0dB points on the side.few questions:1.should I try and keep the DBM mixer saturated at all time?2.If I will have the mixer saturated at the center of the resonace then on the 0dbm frequency it will be saturated plus +20dBm (burned)How do you reccomend to handle such situation?Thanks.https://markimicrowave.com/products/connectorized/mixers/m1-0616mp/datasheet/

author: KE5FX
author_rank: Super Contributor
timestamp: June 15, 2025, 10:42:39 pm
content: Got a link to the paper you're working from?

author: TimFox
author_rank: Super Contributor
timestamp: June 15, 2025, 10:53:42 pm
content: If only one of the LO and RF ports is saturated, then the IF output will depend on the power level applied to the other of those two ports.However, the DC output should still go to zero at 90ophase difference.