TNP #20 - Stanford Research Systems SR830 DSP Lock-in Amplifier Teardown, Repair & Experiments

In this episode Shahriar takes a look at a SRS SR830 DSP Lock-in amplifier. The repair of the instrument is fairly simple and provides a quick look at the internal construction of the unit.
The instrument is then used for characterizing nonlinearities of a pair of matched diodes in large-signal operation. A Tektronix 4-Series is also used alongside the SR830 in DDC mode to show the harmonic behavior of the DUT in frequency domain. The SR830 is able to discern extremely small variation in temperature between the diodes and the resultant 2nd order harmonic changes in both amplitude & phase.
www.TheSignalPath.com
/ thesignalpath​​​
www.Patreon.com/TheSignalPath

[@danmenes3143]

I can think of two effects that might introduce a phase shift: (1) the bulk capacitance of the PN junction, in combination with the 50 ohm termination resistors, would create a phase shift network, and (2) the diodes have a finite carrier lifetime (reverse recovery time). But those look like fast signal diodes, so the t_rr is probably too fast to create a measurable effect. I'm going with the junction capacitance.

[@pabloibaceta5932]

The 4 degrees extra was for the parasitic capacitance of diodes?

[@jessicav2031]

I think the positive phase shift is because the diodes take a different amount of time to turn off vs. turn on. In this case becoming forward biased has to be slower than becoming reverse biased. So at the beginning of the forward bias part of the cycle it is still in reverse bias and the output is higher (less energy is going to ground), then towards the end of that cycle it is "on" (to the extent that it actually is "on" at this voltage) and output is lower. Really great thought-provoking question!

[@pabloibaceta5932]

Thank you as always for such detailed explanations, great video 👍. By the way the hp3400b modification video is my favourite so far, i recommend it at every people i know 😂, even my dog has watched that video..

[@uwezimmermann5427]

I am looking forward to looking at this video - we use three of these in our lab! Yes, these are great instruments - yet essentially quite simple in their function and construction...

[@DrFrank-xj9bc]

LIAs are made for physicists! I also repaired and used several single phase LIAs from P.A.R., EG&G 124A, during my diploma thesis and later for my PhD thesis a dual phase NF3961B for measuring magnetic field response, Χ' and Χ'', from High Tc Super Conductors. The 195Hz output signal was in the µV down to ~10nV level, but the LIA delivered very good SNR and smooth graphs. The Χ' or Real part showed the super conductivity, Χ'' or Imaginary part showed the losses in the S.C. bulk during the normal super conducting phase transition. Later I also measured in parallel the Higher Harmonics of this transition, with high resolution, but this usually required to stack several LIAs, each tuned to the 1st, 2nd, .. 11th, .. harmonics. You would also not be able to measure that in situ with the SR830 alone, as it is not possible to switch the harmonic detection as fast as required. My unique solution then was use of a fast and highly resolving A/D converter, i.e. with 16bit / 100Khz or 18bit/50kHz, giving real SNRs of -96 and -108dB . That was in 1990, so I used the brand new 3458A with frequency and phase locked sampling plus FFT in real time. That was a real challenge at that time, as the PC ran on 20MHz only.. requiring assembly code for the time critical parts of the program. I really love these LIAs as one can extract smallest signals of that specific frequency out of a sea of overwhelming noise.

[@JohnChuprun]

So cool! What an awesome video and experiment. The mind boggles. Thank you.

[@BruceNitroxpro]

This is a perfect video to show what happens in a "real life" application. The diodes are NOT the same... only close.

[@artursmihelsons415]

Great video, as always! Nice and simple demonstration! 👍

[@astronomylabYT]

I've been waiting for years for you or Dave Jones to make a video about this specific LIA. I used one in college for my senior project in Physics and always thought they were really cool!

[@ruhnet]

Fantastic video!

[@LiraLab]

I am really passionate about lock-in amplifiers and LNAs. I've made a capacitance meter (a classic!) with a lock-in amplifier during undergrad and followed up research in LNAs a couple of years later all the way up to the end of my PhD. It's all about those low level signals! This video is so cool! I wonder if you'd be able to model those weak nonlinearities using Volterra series and actually compare the results with the measurements. Anyway, this was an amazing video : )

[@GearAcquisitionSyndrome]

I already miss the 830 I had :(. Nice job! I'm trying to fix a 510 now, but the lack of schematics is frustrating

[@andrewphillip8432]

Hey its one of my favorite lock in amplifiers!

[@JigilJigil]

You should do a video tour of your lab and your equipment.

[@xDevscom_EE]

Null-meters of AC world. I like SRS instruments UI, they not fall for modern GUI world (over)simplification process and still old-school with lot of controls.

[@plemli]

Same here. When I needed an RF vector gen I was eyeing the Tek TSG4106A but found out on this channel that it was identical (save for the fancier UI) to the SRS SG396. The SRS even had all options standard which were $$$ on the Tek and saved me half a car. When you use equipment regularly a non-fancy UI makes sense. The only thing I miss is a RF on/off button that's dedicated instead of being a shift function.

[@christopherjackson2157]

Lock in amplifiers make the best video content. Complicated enough to be interesting ithout being so complicated and esoteric that the video is hard to understand.

[@fluffy_tail4365]

I used this exact instrument to measure raman spectroscopy in a prototype microscope....I had no idea on how it worked and it was pretty fun to figure out how it works

[@motherjoon]

Please do more Stanford research and EG&G instruments.

[@t1d100]

Maybe this is your common practice? For batteries that maintain critical data/calibrations/etc, when you build the new battery, add parallel ports, on the positive and negative leads, so that the next time the battery needs to be replaced, you can just plug in a temporary power source, to hold the settings, while the battery is swapped out.

[@gacherumburu9958]

👍👍

[@mc_cpu]

Didn't get to see inside the interesting bit!

[@karthikvenkat6932]

Can you show how to measure the noise current across the frequency of a photodetector please

[@JW-bd7em]

I used two of these for my PhD! With InGaAs photodiodes.. was wondering if you’d ever do a video on it :D

[@scottpelletier1370]

What do you measure? Tia performance?

[@alexmihai22]

How can I measure the noise of a transistor?

[@pnjunction5689]

Moooar please ;-)

[@nohandleleft]

I'm a former Navy tactical electronic warfare drone so in my case the phase difference would likely be from pop tart crumbs getting inside the patch cord plugs, or more probably I'm simply too lazy to grab another probe from the drawer so I end up routing the signal through the RF distribution unit and across the set room a few times just to reach the panel beside me - all without having to roll my chair the three feet it would take to get it.

[@mortlet5180]

Guys, I've spotted the chAir Force mole! Seriously though, thank you for your service, and for sharing that delightful look inside the Black Art of EW.

[@Creatortech95]

i want help from you I have 2kw pulse amplifier range of 1250 mhz to 1350mhz and 8 of these amp combine together and total out of power combiner expect more than 8kw but the output power is less than 4kw Is it happen because of phase machnig or impedance maching i have vector network anylizer znl 1to 4.5 ghz so why the power out less so much

[@Creatortech95]

also i connect coupler to signal genarator and vna connect to the rf out port and 20db coupler port then i measur the phase using VNA it show the phase angle pinpoint but after amplifier the phase angle of frequency varied i cant undurstand why it happen

[@neomage2021]

I used those every day for years working on spin based quantum computing chips. The programing interface on those is...annoying to say the least.

[@cessromer7078]

Here's an example of how you can implement the interface connection to the SE1022D lock-in amplifier using classes and objects in VBA: ```vba ' Add a reference to the VISA COM 3.0 Type Library ' Go to Tools > References > Browse > select 'National Instruments VISA COM 3.0 Type Library' ' Define a class for the SE1022D lock-in amplifier Class SE1022DLockInAmplifier Private rm As New ResourceManager Private instr As Visa Private timeout As Integer ' Constructor Public Sub Initialize() Set instr = rm.Open("GPIB0::10::INSTR") timeout = 1000 End Sub ' Method to configure the lock-in amplifier Public Sub ConfigureLockInAmplifier() instr.Write "*RST" ' Reset the device to default settings instr.Write "FREQ 1000" ' Set the frequency to 1000 Hz instr.Write "AMPL 1" ' Set the amplitude to 1 V End Sub ' Method to query and print the current settings Public Sub PrintCurrentSettings() instr.Timeout = timeout ' Set the timeout value for the query instr.Write "FREQ?" ' Send the query command Dim freq As String freq = instr.ReadString ' Read the response instr.Write "AMPL?" ' Send the query command Dim ampl As String ampl = instr.ReadString ' Read the response ' Print the current settings Debug.Print "Frequency: " & freq & " Hz" Debug.Print "Amplitude: " & ampl & " V" End Sub ' Destructor Public Sub Terminate() instr.Close rm.Close End Sub End Class ' Main subroutine Sub Main() Dim lockInAmp As SE1022DLockInAmplifier ' Declare a variable for the SE1022D lock-in amplifier ' Create an instance of the SE1022DLockInAmplifier class Set lockInAmp = New SE1022DLockInAmplifier ' Initialize and configure the lock-in amplifier lockInAmp.Initialize lockInAmp.ConfigureLockInAmplifier ' Query and print the current settings lockInAmp.PrintCurrentSettings ' Clean up and release the lock-in amplifier object lockInAmp.Terminate Set lockInAmp = Nothing End Sub ``` In this example, we define a class called `SE1022DLockInAmplifier` to encapsulate the functionality related to the SE1022D lock-in amplifier. The class has methods to initialize and configure the lock-in amplifier, query and print the current settings, and terminate the connection. The main subroutine creates an instance of the `SE1022DLockInAmplifier` class, initializes it, configures the lock-in amplifier, queries and prints the current settings, and then cleans up the resources. Note that you'll need to replace the `"GPIB0::10::INSTR"` with the actual VISA resource string for your SE1022D lock-in amplifier. Ensure that you have the correct VISA address for your specific device. Enjoy.