Zen -> Cen -> Sen, evolution of a minimalistic IV Converter - Page 138 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd March 2013, 10:41 AM   #1371
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
Here is the spectrum according to my Spice model of the cascoded SEN.


Patrick
Attached Images
File Type: png Cascoded SEN FFT.png (63.3 KB, 478 views)
__________________
xen-audio.com
  Reply With Quote
Old 3rd March 2013, 11:02 AM   #1372
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
I have try to cascode the input Jfet , but as you said, doing that causes stability issues.
And stability is the main reason to use this type of circuit.

I prefer the solution that I present in post #1370. I have include the LTspice file. Try it.

edit: for ascurate distortion test and ftt, go to control panel in LTspice and disable compression.


Patrick I am reading your article.
__________________
Sérgio Santos

Last edited by smms73; 3rd March 2013 at 11:12 AM.
  Reply With Quote
Old 3rd March 2013, 03:03 PM   #1373
diyAudio Member
 
Join Date: Apr 2003
Location: Eastern Pennsylvania
Quote:
Patrick I am doing some tests with your circuit ( CEN ) , I think it can be very good solution for PCM1794 as this type of DAC has very high output impedance.
Hi, Sergio,

As you know, one of the complications in designing an I/V for the PCM1794A is how to handle the 6.2mA output bias current. The need to handle this current keeps rearing it's ugly head in the many grounded base/gate circuits that I've designed, where it causes severe D.C. current imbalance and D.C. voltage offset. Summing an offsetting current at the I/V stage's input via an external C.C.S. is one solution, but this adds additional complexity and represents one more element which must be hand trimmed.

Another issue, I feel, complicating the use of grounded base/gate type I/V circuits is the band-limiting of the input signal current. I'm not so concerned about about I/V stage upper harmonics, which are often relatively low and/or out-of-band in grounded base/gate. I'm more concerned about in-band IMD products. Perhaps, the best way to reduce IMD is to band-limit the input signal before applying it to the stage in question. However, simply placing a small capacitor from the DAC's current output to ground seems to upset the grounded base/gate type circuit's THD performance. I suspect this may be because such a bypass cap. transforms what was a high DAC source impedance (good) in to a much lower source impedance (bad). These issues keep driving me back to a simple, low value, passive resistor I/V followed by voltage amplifiction, at least for DAC chips such as the PCM179x series, and the AD1955.

Grounded base/gate circuits attract me becuse of their elegance and wideband performance, but then seem to get tripped up by the implementation details. I suspect that majority of my attraction has to do with their ability to track the wideband DAC output signals relatively accurately, hence, this circuit's popularity in RF signal applications. However, do we really desire accuracy in the handling of signal content above 20KHz, or do we really simply want to ensure that above band signal content does not cause harm to the in band 20Hz-20KHz content? Just my thoughts.
__________________
Ken

Last edited by Ken Newton; 3rd March 2013 at 03:19 PM.
  Reply With Quote
Old 4th March 2013, 12:04 AM   #1374
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Hi Ken,

There is no need to bother too much about the IMD, as the switching frequency of the DAC are much higher than the audio band, the IMD products will be very futher away from the audio band .
I posted a picture of a 5khz sine modulated by 500khz pulse, as you can see, there is harmonics produced by the IMD around the 500khz , 1Mhz and so one but nothing in the audio band.

I think that the high frequency noise from the output of the DAC can be problematic with I/V converters that use feedback , but not with this type of I/V converters, thats the reason I am so interested in this type of I/V converters, of course passive resistor I/V is also a good option , at least with pcm1794 as we see in another thread, but do not forget to filter the high frequency noise before the feedback amplifier.

And as you said adding a capacitor to ground in the input will bring down the impedance , and that is a bad thing, we are better without it.

I will talk about the bias current later.

the 2º and 3º image is the output of the PCM1794 I/V without output capacitor and with 2n2 in parallel with 750 ohms.
Attached Images
File Type: png CEN_IMD.png (84.9 KB, 445 views)
File Type: png output_no_filter.png (557.5 KB, 437 views)
File Type: png output_filter.png (423.0 KB, 307 views)
__________________
Sérgio Santos
  Reply With Quote
Old 4th March 2013, 12:39 AM   #1375
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
This is the SEN version with the conditions of post#1370 the distortion is 0.00009% with 2sk170
Attached Images
File Type: png SEN_Sergio.png (15.3 KB, 333 views)
File Type: png SEN_Sergio_fft.png (49.7 KB, 204 views)
__________________
Sérgio Santos
  Reply With Quote
Old 4th March 2013, 12:47 AM   #1376
diyAudio Member
 
Join Date: Apr 2003
Location: Eastern Pennsylvania
Hi, Sergio,

Yes, the IMD products of 500KHz and 5KHz will be far up at 495KHz and 505KHz. My IMD worries are over the many closely spaced ultrasonic image frequencies produced at multiples of the sampling (or, oversampling) rate. Which, of course, could produce a range of audible baseband components. So, no worries about 5KHz and 500KHz, but worries about 500KHz and 501KHz. The IMD components themselves could even intermodulate with each other. That's the basis of my concern. So, while circuit linearity at high frequencies helps us here, as does bandlimiting the input signal. Grounded base/gate circuits are good at the former, but make difficult to implement the latter.
__________________
Ken
  Reply With Quote
Old 4th March 2013, 07:06 AM   #1377
heb1001 is offline heb1001  China
diyAudio Member
 
Join Date: Sep 2011
Quote:
Originally Posted by smms73 View Post
This is the SEN version with the conditions of post#1370 the distortion is 0.00009% with 2sk170
This is what I was trying to do with #998. Your version is better in simulation. Does it work?
  Reply With Quote
Old 4th March 2013, 10:26 AM   #1378
heb1001 is offline heb1001  China
diyAudio Member
 
Join Date: Sep 2011
Default On the quest for an alternative to batteries...

How about a low frequency (say <100Hz) switched capacitor power supply using low output capacitance solid state relays?

i.e. use solid state relays to switch both sides of a bucket capacitor from a supply to a floating reservoir capacitor followed by a floating regulator.

This one has 1.1pF typical output capacitance:

http://www1.futureelectronics.com/do...0R-1A-F3-A.pdf

So, 4 relays, 2 capacitors and a regulator per floating supply. Some shared logic to sequence the relays. Resulting in 2.2pF stray capacitance from each floating supply to ground.

Any chance of this working?
  Reply With Quote
Old 4th March 2013, 11:13 AM   #1379
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by Ken Newton View Post
Hi, Sergio,

Yes, the IMD products of 500KHz and 5KHz will be far up at 495KHz and 505KHz. My IMD worries are over the many closely spaced ultrasonic image frequencies produced at multiples of the sampling (or, oversampling) rate. Which, of course, could produce a range of audible baseband components. So, no worries about 5KHz and 500KHz, but worries about 500KHz and 501KHz. The IMD components themselves could even intermodulate with each other. That's the basis of my concern. So, while circuit linearity at high frequencies helps us here, as does bandlimiting the input signal. Grounded base/gate circuits are good at the former, but make difficult to implement the latter.
Ken , I have made a test with the circuit of post #1370 that consist in feeding the input with 3 current sources of 10000khz 10005khz and 10002khz. (picture 1 and 2)

Another test with 4 current sources at the input, the 3 of the previous test and with the addicion of 10khz 6ma p-p (picture 3 and 4 )

Picture 1 is the fft at the output without the output filter capacitor , the IMD products are at -93dB

Picture 2 is the fft at the output with the output filter capacitor (2n2) , the IMD products are at -150dB

picture 3 is from the second test and is the input current and the output voltage with the output filter capacitor (2n2)

Picture 4 is the fft at the output with the output filter capacitor (2n2) and the 10khz signal.

In resume : the output filter capacitor in this type of circuit serves also for lowering the distortion caused by the intermodulation of the high frequency noise.

edit: this results are also valid for the original CEN designed by Patrick
Attached Images
File Type: png 10M_IMD_no_filter.png (49.3 KB, 101 views)
File Type: png 10M_IMD_filter.png (45.4 KB, 71 views)
File Type: png IMD_test_waves.png (76.0 KB, 62 views)
File Type: png 10M_IMD_filter_10Khz_6ma.png (46.5 KB, 59 views)
__________________
Sérgio Santos

Last edited by smms73; 4th March 2013 at 11:26 AM.
  Reply With Quote
Old 4th March 2013, 11:14 AM   #1380
heb1001 is offline heb1001  China
diyAudio Member
 
Join Date: Sep 2011
Quote:
Originally Posted by heb1001 View Post
How about a low frequency (say <100Hz) switched capacitor power supply using low output capacitance solid state relays?
PS7901D-1A is 0.75pF typical 1.1pF max and good for 120mA continuous - enough to make a 60mA supply?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
FOR REGA Turntable>>> The heavy weight + Vta adjuster+ceramic ball prooptiki Swap Meet 1 22nd May 2010 05:57 PM
Multi-DAC: Lynx AES16 -> DIR9001/SRC4392 (-> SRC4192) -> PCM1794A novec Digital Line Level 11 11th May 2010 11:57 AM
> Audio <> music <> quick <> synergy <> angst>? rick57 Everything Else 0 4th May 2007 04:03 PM
&gt;&gt;&gt; cheap 50,000uF 60V capacitors here &gt;&gt;&gt; Lubomir Swap Meet 0 1st February 2007 03:36 PM


New To Site? Need Help?

All times are GMT. The time now is 09:00 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2