[SOLVED] Boxcar Averaging Hi-Resolution Mode. - Page 1
Forum section: electronics / testgear

author: Unknown
author_rank: Unknown
timestamp: September 01, 2013, 05:09:11 am
content: Boxcar Averaging Hi-Resolution ModeThe Hi-Resolution / Boxcar averaging Bug.?Is this "Normal" ?"Hi-Resolution Mode in the scope Performs boxcar averaging on thesamples. This reduces white noise and increases the verticalresolution of the waveform."so far so good,BUT have found something strange...just want to know if this is "normal" in other boxcar averaging scopes,or if its just a Firmware Bug, or a Memory Limitation, or a Decimation Bug.?The Bug is frequency dependant & has phase cancellations:At 10ms.124KHz SQuare wave measures 740mV~756mVat 263khz goes down to 240mV~250mV,but if i select Normal Sampling Mode, or Peak Detect, or Normal Average >2, the Bug disappears.At 1second Horizontal the SQR Waveform disappears at 3.03KHz & 6.11KHz & 9.12KHz & 12.23KHz,At:200ms/div Waveform disappears at 12.2KHz & 48.8KHz & 97.7KHz & 194.99KHz.100ms/div Waveform disappears at 48.8KHz & 97.7KHz & 194.99KHz & 244.74KHz.50ms/div Waveform disappears at 194.99KHz, etc...20ms/div Waveform disappears at 194.99KHz, etc...this goes on & on, the smaller the Horizontal/div, the fastest must be the Frequency to Resonate with the Boxcar algorithm.My question:This also happens in Tektronik DPO5000 ? Agilent X4000A ? Rigol DS6000? LeCroy Wavesurfer MXs-B ?any other 5GSa/s Scope?Scope:Instek GDS-3352FW v1.21Frequency Generator:Leader LAG-25have tested 50ohm in-line termination, 600ohm.is not a termination issue, normal sampling is ok, flat.Thanks.PS.found something interesting...http://www.wavemetrics.com/products/igorpro/dataanalysis/signalprocessing/smoothing.htmhttp://terpconnect.umd.edu/~toh/spectrum/Smoothing.html

author: larry42
author_rank: Regular Contributor
timestamp: September 01, 2013, 10:38:20 am
content: Check your sample rates. I'm sure it's an undersampling problem...

author: Unknown
author_rank: Unknown
timestamp: September 01, 2013, 09:04:43 pm
content: Quote from: larry42 on September 01, 2013, 10:38:20 amit's not a sampling problem...when i lay down in bed, blood flows easy into the brain, and the answer pops up easy.The Conclusion:Firmware v1.08: the Boxcar Average Filter "Hi-Resolution Mode" was controlled only by the HW Frequency Counter, controlled by the Trigger.does not matter how i moved the Horizontal/div knob, the Boxcar filter does not move, because it's following the Frequency counter.Firmware v1.21: Boxcar Filter is controlled by the Horizontal Knob,when i change time/div, the filter cutoff changes.That's why i thought it was a bug, + the lack of a ChangeLog.txt in the Firmware update.for example, 1st video:100ms/div = 10Hz/div100Hz/screenFilter Kicks-in at aprox. 24.4Khz, and Waveform noise is totally filtered "disappears" at 48.8KHz, the filter rings at 97.7KHz, 194.99KHz & 244.74KHz caracteristic of the Boxcard Lowpass algorithm.for:10ms/div is 100Hz/div.1KHz/screen.Filter kicks-in aprox. at 124KHz, "Square wave is flat upto",at 263khz goes down, because of the low pass filter slope.but if i select Normal Sampling Mode, or Peak Detect, or Normal Average >2, the "Bug" disappears, because is not a Bug.is the filter slope & the caracteristic ringing, following the screen not frequency counter.at 100uS/div = 10khz/div100KHz/screen.the 11.2896MHz frequency is falling, "the Boxcar filter has kick-in, much lower."because the filter kicks in near 10000KHz or 10MHz,the filter is designed to kick in at aprox. 100x the frequency of the total screen, and at aprox. 200x for the low freqs.the filter eliminates all frequencies at 200x times the frequency & rings at x2, x4, x8...at 50uS, the Square wave is Flat.50us/div = 20KHz/div200KHz/screen.the filter kicks in near 20000KHz or 20MHz,at 200us/div the 11MHz SQR waveform disappears completly "completly filtered".200us/div = 5KHz/div,50KHz/screen.the filter kicks in near 5000KHz or 5MHz,Not a Bug, just a change in the FW to increase DSP, FPGA, ASIC efficiency & how the filter kicks-in.I think this change is becouse the Alternate Trigger, is not able to Trigger dual Hardware Frequency Counters.This is a method allows to have dual, triple or quad channel {Hi-Resolution mode} Active with {Alternate Trigger} Active, but with 1 HW Frequency Counter.

author: larry42
author_rank: Regular Contributor
timestamp: September 01, 2013, 10:36:01 pm
content: Quote from: JuanPC on September 01, 2013, 09:04:43 pmI understand that English is not your first language, so it's very hard for me to follow your logical argument, but I still thinkn that it's a under-sampling issue -From what I can tell your scope is a 350MHz model with 5Gsps or something, but only 25kpts/channel.This means that in the slow time-base settings your sampling rate is memory limited.your write in teh first post:"200ms/div Waveform disappears at 12.2KHz & 48.8KHz & 97.7KHz & 194.99KHz."with 10 divisions per screen, those 25kpts are divided over 1sec of time, at 200ms/divThat means that the effective sampling rate is 25ksps, and you would expect a null in your spectrum at 25kHz, and multiples thereof.Now the boxcar filter probably operates on the sample memory, and if it takes an average of two samples, I would expect it to have a null at 12.5kHz (and odd multiples of that frequency)...Now if the boxcar filter is a average of two points, it will

author: Unknown
author_rank: Unknown
timestamp: September 02, 2013, 05:12:48 am
content: Quote from: larry42 on September 01, 2013, 10:36:01 pmIf it were a memory problem, Normal Sampling Mode would also be affected, and any other sampling mode, Peak & Normal Average."Problem" was that: when i upgraded the firmware,found that, when looking a frequency 200x times higher than the visible on the screen per time/div,makes the Square wave disappear, but only in Hi-Resolution mode.That didn't happened with older firmware,because the Hi-Resolution Boxcar algorithm, was following the Frequency counter of the waveform, not the screen time/div,if frequency moves up, the filter moves up, and i can never reach the other side of the filter.but because Scope has an Alternate Trigger On/Off "dual Trigger/one for each channel in a dual channel scope"*that feature was changed to allow Hi-Resolution Mode in every channel independently,that would be impossible with 1 hardware Frequency counter per Oscilloscope,the ideal method would be to have a hardware Frequency counter per channel, and each Boxcar algorithm following each frequency counter in every channel.*don´t know if the 4 channel version has 4 triggers.Relation of sample rate, memory & time is:Capture Interval = 1/Sample Rate X Memory.&Capture Interval/10 = Time Per Division.Every Scope has a Sweet Spot, where refresh rate, sample rate, wfm/s are the best.Because of Memory Depth Limitations the Sample Rate Changes,Because of Speed Limitations the wfm/s Changes.but the Boxcar algorithm is just a very strong brick wall low pass filter, at a very high frequency following the maximum visible screen frequency,Variable, not fixed like BW Limit,it´s like a super smart Bandwidth Limit, similar to a "Rocktron HUSH Noise Reduction." that follows an envelope follower,cleaning up the signal of sometimes unnecessary hi-frequency noise but keeping the super fast rise times & all the advantages of a high speed scope when working at low speed.As far as I know is Not Possible to Maintain max-settings constant in every setting, at least in this price range.Here is a table for this scope:Settings vs. Memory Depth.-Sample Rate vs. Time/div.:25 SPS: 100s/div <--- From Here Starts Roll. <--- 25Kpts can record 1000sec. or 16.6 minutes at this time/div.50 SPS: 50s/div <--- Records >8min.100 SPS: 20s/div250 SPS: 10s/div500 SPS: 5s/div.1 KSPS: 2s/div.2.5KSPS: 1second/div.5 KSPS: 500ms *** Here Starts the Fun.10KSPS: 200ms/div.25KSPS: 100ms/div. <--- Roll Mode Ends Here. <--- Records 1sec. Of data at this time/div.50KSPS: 50ms/div.100KSPS: 20ms/div.250KSPS: 10ms/div.500KSPS: 5ms/div.1 MSPS: 2ms/div.2.5MSPS: 1ms/div. ---> Records 10ms. data.5 MSPS: 500us/div. ---> Records 5ms. data.10MSPS: 200us/div. ---> Records 2.5ms. data.25MSPS: 100us/div. ---> Records 1ms. data.50 MSPS: 50us/div. ---> Records 500us. data.100 MSPS: 20us/div. ---> Records 250us. data.250 MSPS: 10us/div. ---> Records 100us. data.500 MSPS: 5us/div. ---> Records 50us. data.1 GSPS: 2us/div. ---> Records 25us. data.2.5GSPS: 1us/div. ---> Records 10us. data.5 GSPS: 500ns/div.5 GSPS: 200ns/div.5 GSPS: 100ns/div.5 GSPS: 50ns/div. *** Here Starts the Rising Edge Fun.!5 GSPS: 20ns/div. <-----Here is Real 5GSa/s, no ET, Measuring Jitter in all its Glory!******************** Here is the Limit of RealTime.25Kpts at 5GSa/s 20ns/div allows to record 5us. of data.Basically if you hit , and go back in <Horizontal Time/div>, the 25Kpts allows to capture a full screen at that resolution, and half screen at 1 time/div back, or 1/5 screen <<2 time/div back....if  at1ms/div, 25Kpts captures full screen, when moving the <<Horizontal to2ms, shows ½ screen of data, at 5ms shows 1/5 data., 10ms shows 1/10 data, 20ms/div shows 1/20 screen data.So when dealing with 25kpts memory [Run/Stop] it´s not a Magic button where you push and look everything, must be done meticulously,.******************** The Equivalent Time Starts Here.ET 10 GSPS Equivalent Time, or 5 GSPS [sin(x)/x]: 10ns/div.ET 20 GSPS or 5 GSPS: 5ns/div.ET 50 GSPS or 5 GSPS: 2ns/div.ET 100 GSPS or 5 GSPS: 1ns/div. ***Here is how it would look in a $1/4 Million dollar scope in RealTime.The Scope has 2 modes, Equivalent Time &/or [sin(x)/x]ET looks digital without VPO, with VPO-Active works the same way, but with average sampling, not real sampling, a bit slow.[sin(x)/x] looks Amazing, like Real Time VPO.Equivalent Time was designed to increase the time divisions "less than <20ns/div" and increase resolution.5GSa/s has 200ps per sampling point,This scope cannot go lower than 1ns.1ns = 1000ps, has 5 sampling points at 1ns, but ET & [sin(x)/x] looks like if it had more SamplingPoints.10sp at 2ns,25sp at 5ns50sp at 10ns …100sp at 20ns RT.5 sampling points are needed minimum to measure a Sine wave, like a Triangle.!.. . ..

author: larry42
author_rank: Regular Contributor
timestamp: September 02, 2013, 09:09:31 am
content: Quote from: JuanPC on September 02, 2013, 05:12:48 amPlease explain what you were expecting to see here: "when looking a frequency 200x times higher than the visible on the screen per time/div". When you're undersampling by that much then all bets are of (and this is what peak-detect mode is for)I don't know what you mean by "because the Hi-Resolution Boxcar algorithm, was following the Frequency counter of the waveform" - I don't understand the term "frequency counter" that you keep on referring to.

author: BravoV
author_rank: Super Contributor
timestamp: September 02, 2013, 09:31:57 am
content: Larry42, save your energy, here a hint and read thoroughly to get a clue ->HERE

author: Unknown
author_rank: Unknown
timestamp: September 02, 2013, 09:44:57 pm
content: Quote from: larry42 on September 02, 2013, 09:09:31 amAlmost All DSO have a built-in Hardware Frequency counter, excluding Agilent X3000A its a software counter, this one is 20ppm high precision.it measures the frequency of the waveform, and shows in the right bottom corner of the screen [(F) XX.XXXX Hz].http://en.wikipedia.org/wiki/Frequency_counterhttp://en.wikipedia.org/wiki/Parts_per_millionwas trying to see Aliasing Artifacts,good scopes have less or none.bad scopes have severe aliasing artifacts.didn´t see.http://en.wikipedia.org/wiki/Aliasing

author: larry42
author_rank: Regular Contributor
timestamp: September 03, 2013, 11:17:33 am
content: Quote from: BravoV on September 02, 2013, 09:31:57 amI don't understand how that post helps, but ok, I'm kind of done trying to help people on this forum, as the language barriers make many technical discussions nearly impossible (FWIW, English is not my mothertongue either, nor do I live an in an english speaking country)

author: BravoV
author_rank: Super Contributor
timestamp: September 03, 2013, 11:24:06 am
content: Quote from: larry42 on September 03, 2013, 11:17:33 amI believe the OP knowledge on test & measurement area ...err.. lets say "abit" lacking, and doubt he understand it at all.Read that thread again, see how he proposed using a "PC based sound card"to measure a clock jitter and "rise time" of < 100 ps (pico second) signal.

author: Unknown
author_rank: Unknown
timestamp: September 03, 2013, 06:14:57 pm
content: Quote from: BravoV on September 03, 2013, 11:24:06 ami have my first enemydude 192Khz x 2 channels x 32 bits (24-signal + 8 control bits) = 12288000 bits per second. = 81.38ns period.Rise Time & Jitter of 1% period is too much.1% of a period @ 12.288MHz = 0.8138ns = 813ps.0.1%=81.3ps0.01%=8.13ps0.002%=1.628psSaw waves are even harmonic,Square waves are odd harmonic,jitter causes misalignment of the harmonics, easy to see with most audio softwares like Sonar.-more misalignment = more jitter.less misalignment = less jitter.the test just needs a mathematically generated Saw wave, with no misalignment.& record DA-AD with different clocks.done it, here is the result:

author: macboy
author_rank: Super Contributor
timestamp: September 03, 2013, 11:31:32 pm
content: ^^^ Oh my!

author: BravoV
author_rank: Super Contributor
timestamp: September 04, 2013, 12:31:01 am
content: Quote from: JuanPC on September 03, 2013, 06:14:57 pm