Audio Signal Isolation Techniques - Analog Optocouplers
Sometimes it desirable to isolate analog signals.
This can be done in some different ways.
We can use separate power supplies for the source
and the receiver. But then we still have a common
earth rail. This rail can transmitt disturbance, noise, hum
and distort the signal.
- One way is to use diffential amplifiers or use balanced configuration.
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If we want to separate the common ground, and isolate
the source and receiver totally there are also
some different techniques.
- Transformers. There are very high quality audio transformers
nowadays. The can cost some money and are not commonly available.
------------------------------------------------
Light can be used to transmitt, like we do in infra-red remote controls. This can be done in several ways.
- LDR, light dependent resistors are around
with good analog linearity.
VacTec VTL5C3 is good fotoresistor.
- Optocouplers use light to transmitt. Linearity is not so good, what I have found out from todays constructions.
Optocouplers are mostly used for digital signals. Very high speeds can be used for digital tranfers.
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There are however some optocouplers that maybe can be used for analog, audio signals.
Hewlett Packard CNR200 is one.
Texas Instruments TIL300 is another.
This one is interesting because it allows feedback correction of the signal. Light is shared by 2 light sensing fotodiodes.
This TIL300 was used in a circuit in my Swedish Elektor 1/98 (can be last editon of 1997 in original Elektor).
See the diagram of the princip, taken from TIL300 datasheet.
http://www.taosinc.com/pdf/til300.pdf
The circuit used simple OP-amps TLC271, but still distortion was low
with a signal 10Vpp at single 12Vdc supply.
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Does anyone know about other good devices for audio signal isolation?
They can be used in feedback, both in amplifiers and power supplies.
And wherever it is needed some total isolation of signals,
to avoid unwanted disturbances.
/halo - not completely isolated - as long as he has diyaudio.com
Sometimes it desirable to isolate analog signals.
This can be done in some different ways.
We can use separate power supplies for the source
and the receiver. But then we still have a common
earth rail. This rail can transmitt disturbance, noise, hum
and distort the signal.
- One way is to use diffential amplifiers or use balanced configuration.
---------------------------------------------------------------
If we want to separate the common ground, and isolate
the source and receiver totally there are also
some different techniques.
- Transformers. There are very high quality audio transformers
nowadays. The can cost some money and are not commonly available.
------------------------------------------------
Light can be used to transmitt, like we do in infra-red remote controls. This can be done in several ways.
- LDR, light dependent resistors are around
with good analog linearity.
VacTec VTL5C3 is good fotoresistor.
- Optocouplers use light to transmitt. Linearity is not so good, what I have found out from todays constructions.
Optocouplers are mostly used for digital signals. Very high speeds can be used for digital tranfers.
-----------------------------------------------
There are however some optocouplers that maybe can be used for analog, audio signals.
Hewlett Packard CNR200 is one.
Texas Instruments TIL300 is another.
This one is interesting because it allows feedback correction of the signal. Light is shared by 2 light sensing fotodiodes.
This TIL300 was used in a circuit in my Swedish Elektor 1/98 (can be last editon of 1997 in original Elektor).
See the diagram of the princip, taken from TIL300 datasheet.
http://www.taosinc.com/pdf/til300.pdf
The circuit used simple OP-amps TLC271, but still distortion was low
with a signal 10Vpp at single 12Vdc supply.
------------------------------------------------------
------------------------------------------------------
Does anyone know about other good devices for audio signal isolation?
They can be used in feedback, both in amplifiers and power supplies.
And wherever it is needed some total isolation of signals,
to avoid unwanted disturbances.
/halo - not completely isolated - as long as he has diyaudio.com
Attachments
Re: Transformer ?
An orignal idea of mine. I have never seen it before.
Of course is has to do with Amplifiers, as this is
my special area of interest.
Thanks for asking, Dave.
/halo - has Top Secret Folders - in his FTP-Server
Beware - Curiosity Killed My Cat .....
Yes, I really have.DRC said:
An orignal idea of mine. I have never seen it before.
Of course is has to do with Amplifiers, as this is
my special area of interest.
Thanks for asking, Dave.
/halo - has Top Secret Folders - in his FTP-Server
Beware - Curiosity Killed My Cat .....Well, even I Halojoys intended use is top secret, there is a
common problem which is not secret: Connecting a PC to the
stereo. This can cause various types of problems, depending
on circumstances, and which could be solved by galvanic
isolation of one sort or another. Hence, I have also been
thinking about this problem and considered various solutions,
including opto-couplers. I am somewhat sceptical towards
using optocouplers, but I have no experience with using them,
so maybe it is unfounded. I have also been considering those
optocouplers with "feedback" that Halojoy referred to. I haven't
built or tested anything yet, since this is not of priority
concern to me, but I lean towards using differential drivers and
receivers with a capacitive barrier in between.
common problem which is not secret: Connecting a PC to the
stereo. This can cause various types of problems, depending
on circumstances, and which could be solved by galvanic
isolation of one sort or another. Hence, I have also been
thinking about this problem and considered various solutions,
including opto-couplers. I am somewhat sceptical towards
using optocouplers, but I have no experience with using them,
so maybe it is unfounded. I have also been considering those
optocouplers with "feedback" that Halojoy referred to. I haven't
built or tested anything yet, since this is not of priority
concern to me, but I lean towards using differential drivers and
receivers with a capacitive barrier in between.
I have a bunch of these
these devices are used in biomedical applications for isolation of the patient from the mains outlet ! useful also if you have a microprocessor application hooked into your PC and you want to protect an ADC and MCU from stray high voltages getting onto your motherboard and frying your machine.
I have both HCNR-200 and 201, the latter is a mil-spec device, let me know at jack@tech-diy.com if you need them to play around with. Agilent states linearity of 0.01% for the HCNR-201 and I can confirm that this figure is beaten most of the time.) I also have some HCPL-7840's but these are tricky to implement.
since you are using an op-amp with a photo-diode (and what the PDF's don't tell you) is that you have to be pretty careful compensating for the photodiode capacitance. these things are easy to get oscillating. Burr-Brown (at www.ti.com ) has about the best application notes on taming photodiode amplifiers.
the TIL300 is made by Texas Advanced Optical ( www.taosinc.com ) -- they purchased a lot of TI's analog optics product line. I use their TSL230's and TSL235's. They also make pretty acurate RGB sensors. The TIL300 line is distributed by Future-Active in the US. There is another product, the IL300 from Vishay, but I haven't played with these.
these devices are used in biomedical applications for isolation of the patient from the mains outlet ! useful also if you have a microprocessor application hooked into your PC and you want to protect an ADC and MCU from stray high voltages getting onto your motherboard and frying your machine.
I have both HCNR-200 and 201, the latter is a mil-spec device, let me know at jack@tech-diy.com if you need them to play around with. Agilent states linearity of 0.01% for the HCNR-201 and I can confirm that this figure is beaten most of the time.) I also have some HCPL-7840's but these are tricky to implement.
since you are using an op-amp with a photo-diode (and what the PDF's don't tell you) is that you have to be pretty careful compensating for the photodiode capacitance. these things are easy to get oscillating. Burr-Brown (at www.ti.com ) has about the best application notes on taming photodiode amplifiers.
the TIL300 is made by Texas Advanced Optical ( www.taosinc.com ) -- they purchased a lot of TI's analog optics product line. I use their TSL230's and TSL235's. They also make pretty acurate RGB sensors. The TIL300 line is distributed by Future-Active in the US. There is another product, the IL300 from Vishay, but I haven't played with these.
Halo,
What about ...
RF coupling ? With optical coupling / transformers / capasitors that pretty much covers the usable electromagnetic spectra.
Acoustic / vibrational coupling ? I doubt if this would be useful in audio ! (I did once use ultrasonics to get a signal through a 600mm thick steel wall but the quality was poor, to say the least)
Dave - only slightly curious
What about ...
RF coupling ? With optical coupling / transformers / capasitors that pretty much covers the usable electromagnetic spectra.
Acoustic / vibrational coupling ? I doubt if this would be useful in audio ! (I did once use ultrasonics to get a signal through a 600mm thick steel wall but the quality was poor, to say the least)
Dave - only slightly curious
I only looked at the dynamic range over a 3 decade interval -- take a look at the application notes from Vishay very carefully -- you can bias the servo diode and increase the range very dramatically (at the cost of more parts, you need a CCS). <p> If you were really creative you could also use the diode to take a logarithm and then exponentiate on the other side -- the temperature dependency would null out since you would be using a diode with the same temperature on the same substrate to exponentiate.<p>At any rate, these were beyond the scope of my project -- interesting for an EE student, I am sure.
If you have a DAC ...
Christer,
I had a big problem with this due to RF interferance
from a cable TV / cable modem.
No amount of ferite seem to make any difference !!
I now use a cheap sound-blaster 5.1 and
use the SPDIF output to drive a coaxial /
optical buffer (£15 GBP) and then into a DAC.
Only problem with this setup is the SB uses
a 48K sample rate with upsampling if I
play a CD
. I think the Audigy cards
can run the DSP's at different speeds though ..
Dave
Christer,
I had a big problem with this due to RF interferance
from a cable TV / cable modem.
No amount of ferite seem to make any difference !!
I now use a cheap sound-blaster 5.1 and
use the SPDIF output to drive a coaxial /
optical buffer (£15 GBP) and then into a DAC.
Only problem with this setup is the SB uses
a 48K sample rate with upsampling if I
play a CD
. I think the Audigy cardscan run the DSP's at different speeds though ..
Dave
I believe that CPClare isolators have the best linearity on the market right now. That info may be old, but it was true not too long ago, though I think a transformer would be better. I had a crazy idea once to isolate the power stage of an amplifier from the other stages. I could use a bit of feedback with another optocoupler to lower the overall distortion. However, I came to the conclusion I could achieve the same results with good grounding.
On a completely different topic, the adum1100 is probably the best digital coupler you can get in terms of not adding time distortion.
Alvaius
On a completely different topic, the adum1100 is probably the best digital coupler you can get in terms of not adding time distortion.
Alvaius
Yes, that is what I think also.PMA said:
Hope for some development of New Optocouplers for Analog.
The demand for digital opto has driven those ones
forward to very high levels.
Still there is much to wish for, both in low noise, linearity and analog bandwidth.
How are those LDR-devices?
I have heard they are suitable for Audio.
VacTec VTL5C3 - VTL5C3/2 is a resistor divider.
Found some datasheet at www.aikenamps.com
Also there a datasheet of a PhotoFET - H11F1 PhotoFET optocoupler - (.pdf format)
http://www.aikenamps.com/TI_datasheets.htm
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Optical Isolators (VACTROLs®)
/halo
According to Horowitz and Hill, isolation amplifiers use one of three methods:
1. Transformer isolation of a high-frequency carrier signal - for relatively low bandwidth signal (DC to around 10 kHz) - made by Analog Devices, and Burr-Brown (3656)- require DC power on only one side - can isolate up to 3.5 kV and typically have bandwidths to 2kHz.
2. Optically coupled signal transmission (signal sent by LED, received by photodiode) - typified by Burr-Brown ISO100 - requires power supplies at both ends - can isolate up to 750 volts and has 60 kHz bandwidth.
3. Capacitively coupled isolation of high-frequency carrier signal - tpyified by Burr-Brown's ISO102, ISO106, ISO122 - most models requires power supplies at both ends - ISO106 isolates to 3.5 kV and has 70 kHz bandwidth.
Costs range from $25 to $100 each. Burr-Brown offers a wide selection of isolation amplifiers.
There are also analog optocouplers available which provide close to linear output. Andy suggested the Hewlett Packard CNR200/CNR201 which has 0.01% nonlinearity and wide bandwidth of DC to > 1MHz. They are available for about $2.50/ea.
Another option is the CP Clare LOC110 series (datasheet available). Also worth checking out is the NEC PS8601 (available at Mouser so no minimum order).
http://web.mit.edu/tas/www/2JOC/notes/2joc-not.htm
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High-Linearity Analog Optocouplers Technical Data - HCNR200
/halo - bureau of investigation at work
1. Transformer isolation of a high-frequency carrier signal - for relatively low bandwidth signal (DC to around 10 kHz) - made by Analog Devices, and Burr-Brown (3656)- require DC power on only one side - can isolate up to 3.5 kV and typically have bandwidths to 2kHz.
2. Optically coupled signal transmission (signal sent by LED, received by photodiode) - typified by Burr-Brown ISO100 - requires power supplies at both ends - can isolate up to 750 volts and has 60 kHz bandwidth.
3. Capacitively coupled isolation of high-frequency carrier signal - tpyified by Burr-Brown's ISO102, ISO106, ISO122 - most models requires power supplies at both ends - ISO106 isolates to 3.5 kV and has 70 kHz bandwidth.
Costs range from $25 to $100 each. Burr-Brown offers a wide selection of isolation amplifiers.
There are also analog optocouplers available which provide close to linear output. Andy suggested the Hewlett Packard CNR200/CNR201 which has 0.01% nonlinearity and wide bandwidth of DC to > 1MHz. They are available for about $2.50/ea.
Another option is the CP Clare LOC110 series (datasheet available). Also worth checking out is the NEC PS8601 (available at Mouser so no minimum order).
http://web.mit.edu/tas/www/2JOC/notes/2joc-not.htm
################################################################
High-Linearity Analog Optocouplers Technical Data - HCNR200
/halo - bureau of investigation
at workAnother method is to use a Voltage to Frequency chip (or discrete circuit) which converts your analog input signal to a frequency. From there you use a standard (but fast) opto-isolator or opto-coupler IC. On the Secondary (!) you then use a Frequenct to Voltage chip to convert back to Analog.
I have used a Bur-Brown products such as a VFC320.
I have used a Bur-Brown products such as a VFC320.
Yes, that is one method for sending signals.crown300 said:
Another one is using, ADC - opto - DAC.
I want to use applications that are more direct
that can be a part of a circuit like a component.
This is Hewlett Packard HCNR200
High Linearity Analog Optocouplers, uses 2 photodiode techniques.
One can be used to correct the signal via feedback.
Attachments
Crown,
that's right, but imagine that you would like to achieve SNR of 100dB and THD better than 0.01%. Not easy with VFC/FVC. Voltage to frequency to voltage conversion gives you about 60 - 70 dB SNR only and fast response by high order filters must be assured. Linearity in order of 0.1% when fast enough. This is how I transfer analog signals/transients by optical fibre from high-voltage potential.
Pavel
that's right, but imagine that you would like to achieve SNR of 100dB and THD better than 0.01%. Not easy with VFC/FVC. Voltage to frequency to voltage conversion gives you about 60 - 70 dB SNR only and fast response by high order filters must be assured. Linearity in order of 0.1% when fast enough. This is how I transfer analog signals/transients by optical fibre from high-voltage potential.
Pavel
halojoy,
I use ISO122 and AD215 as a standard. Especially AD215 is a remarkable circuit. But again - it is not enough for true hi-end audio.
Pavel
P.S. you can visit my professional web page, i.e. http://www.pha.inecnet.cz/macura
I use ISO122 and AD215 as a standard. Especially AD215 is a remarkable circuit. But again - it is not enough for true hi-end audio.
Pavel
P.S. you can visit my professional web page, i.e. http://www.pha.inecnet.cz/macura
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