differences between shunt and series voltage references?

Discussion in 'Electronic Design' started by Michael Noone, Jul 11, 2005.

  1. Hi - I need a 4.096 voltage reference for an ADC. I'd like it to be as
    accurate as possible, naturally. I've been looking at the various 4.096
    voltage references (Maxim alone makes about 45) - and I've noticed that
    they for the most part can be grouped as either shunt or as series voltage
    references. From what I can tell a shunt V reference is just a zener diode
    of the rated voltage. A series V reference is just a voltage regulator. Is
    this right? Does one have a major advantage over the other? Thanks for your
    help!

    -Michael Noone
    Michael Noone, Jul 11, 2005
    #1
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  2. Michael Noone

    Guy Macon Guest

    Michael Noone wrote:

    >Hi - I need a 4.096 voltage reference for an ADC. I'd like it to be as
    >accurate as possible, naturally. I've been looking at the various 4.096
    >voltage references (Maxim alone makes about 45) - and I've noticed that
    >they for the most part can be grouped as either shunt or as series voltage
    >references. From what I can tell a shunt V reference is just a zener diode
    >of the rated voltage. A series V reference is just a voltage regulator. Is
    >this right? Does one have a major advantage over the other? Thanks for your
    >help!


    Look here:
    Understanding Voltage-Reference Topologies and Specifications
    [ http://pdfserv.maxim-ic.com/en/an/AN719.pdf ]

    --
    Guy Macon <http://www.guymacon.com/>
    Guy Macon, Jul 11, 2005
    #2
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  3. On Sun, 10 Jul 2005 20:03:47 -0500, the renowned Michael Noone
    <mnoone.uiuc.edu@127.0.0.1> wrote:

    >Hi - I need a 4.096 voltage reference for an ADC. I'd like it to be as
    >accurate as possible, naturally. I've been looking at the various 4.096
    >voltage references (Maxim alone makes about 45) - and I've noticed that
    >they for the most part can be grouped as either shunt or as series voltage
    >references. From what I can tell a shunt V reference is just a zener diode
    >of the rated voltage. A series V reference is just a voltage regulator. Is
    >this right? Does one have a major advantage over the other? Thanks for your
    >help!
    >
    >-Michael Noone


    Aside from series vs. shunt, some ADCs are quite demanding as far as
    the reference output impedance goes.

    This is a pretty accurate (0.05%) and stable (and low current)
    reference for the price:

    http://www.analog.com/UploadedFiles/Data_Sheets/564838270REF19x_h.pdf



    Best regards,
    Spehro Pefhany
    --
    "it's the network..." "The Journey is the reward"
    Info for manufacturers: http://www.trexon.com
    Embedded software/hardware/analog Info for designers: http://www.speff.com
    Spehro Pefhany, Jul 11, 2005
    #3
  4. Michael Noone wrote:
    > Hi - I need a 4.096 voltage reference for an ADC. I'd like it to be as
    > accurate as possible, naturally. I've been looking at the various 4.096
    > voltage references (Maxim alone makes about 45) - and I've noticed that
    > they for the most part can be grouped as either shunt or as series voltage
    > references. From what I can tell a shunt V reference is just a zener diode
    > of the rated voltage. A series V reference is just a voltage regulator. Is
    > this right?


    Yes.

    Does one have a major advantage over the other? Thanks for your
    > help!


    You have to compare the specs for noise and disturbance rejection.
    The series reference often uses less current than a shunt reference
    fed by just a resistor, if the raw voltage varys over a wide range.
    John Popelish, Jul 11, 2005
    #4
  5. Michael Noone

    Robert Baer Guest

    Michael Noone wrote:

    > Hi - I need a 4.096 voltage reference for an ADC. I'd like it to be as
    > accurate as possible, naturally. I've been looking at the various 4.096
    > voltage references (Maxim alone makes about 45) - and I've noticed that
    > they for the most part can be grouped as either shunt or as series voltage
    > references. From what I can tell a shunt V reference is just a zener diode
    > of the rated voltage. A series V reference is just a voltage regulator. Is
    > this right? Does one have a major advantage over the other? Thanks for your
    > help!
    >
    > -Michael Noone

    I strongly suggest you look for *any* other brand; Maxim has the bad
    habit of advertising vaporware.
    Robert Baer, Jul 11, 2005
    #5
  6. Michael Noone

    Ban Guest

    Spehro Pefhany wrote:
    > On Sun, 10 Jul 2005 20:03:47 -0500, the renowned Michael Noone
    > <mnoone.uiuc.edu@127.0.0.1> wrote:
    >
    >> Hi - I need a 4.096 voltage reference for an ADC. I'd like it to be
    >> as accurate as possible, naturally. I've been looking at the various
    >> 4.096 voltage references (Maxim alone makes about 45) - and I've
    >> noticed that they for the most part can be grouped as either shunt
    >> or as series voltage references. From what I can tell a shunt V
    >> reference is just a zener diode of the rated voltage. A series V
    >> reference is just a voltage regulator. Is this right? Does one have
    >> a major advantage over the other? Thanks for your help!
    >>
    >> -Michael Noone

    >
    > Aside from series vs. shunt, some ADCs are quite demanding as far as
    > the reference output impedance goes.
    >
    > This is a pretty accurate (0.05%) and stable (and low current)
    > reference for the price:
    >
    > http://www.analog.com/UploadedFiles/Data_Sheets/564838270REF19x_h.pdf
    >
    >
    >
    > Best regards,
    > Spehro Pefhany


    But the dropout voltage is so high, it cannot be fed from the +5V rail, here
    is a brand new reference REF3240
    http://focus.ti.com/docs/prod/folde...P=hpa_dc_general&HQS=NotApplicable PR sc05144
    it needs only 100mV for an output current of 8mA, and just 1mV if the
    current is 1uA.
    --
    ciao Ban
    Bordighera, Italy
    Ban, Jul 11, 2005
    #6
  7. Michael Noone

    PeteS Guest

    Just to add another option...

    I also like the National LM4120 for A-D references. I am using this as
    a reference for an existing A-D subsystem (not high speed, I must admit
    - system voltage monitoring in this application).

    I am using the LM4120AIM5-4.1 which has the following specs:

    180mV dropout at 1mA (worst case, typical = 120mV)
    +/-5mA sink OR source
    50ppm tempco
    Output noise voltage 20uV p-p 0.1Hz - 10Hz, 36uV p-p 10Hz - 10kHz
    Zo < 1 ohm for F < 10kHz ( at Iout = 1mA)

    Comes in a nice SOT23-5 package.

    Cheers

    PeteS
    PeteS, Jul 11, 2005
    #7
  8. Robert Baer <> wrote in
    news:NeqAe.6294$:

    > I strongly suggest you look for *any* other brand; Maxim has the
    > bad
    > habit of advertising vaporware.


    Do you mean that they advertise alot of products that they never bring to
    market? I noticed they had a couple really nice SOT-23 V-regs - and then I
    realized that I couldn't find a distributor for *any* of the accurate ones.
    I also noticed they don't have samples available for these parts - so it
    seems to me that any parts that they have samples available for
    available... Thus I was lookin at the Maxim MAX6126:

    http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3623

    ..06% initial accuracy and it comes in a 8-uMAX package. (it says .02% on
    the above page but the 4.096 8-uMAX part is .06% if you look at pg. 16 of
    its datasheet) It does need a couple external components though (some small
    capacitors). It also seems to be available as a sample - though I couldn't
    find any distributor that stocked it. This is not a big deal as a total of
    6 of these units will be made. I have made a sample request of this part -
    I guess I'll have to see if it actually comes.

    Does that look like a good choice?

    -Michael
    Michael Noone, Jul 11, 2005
    #8
  9. On Sun, 10 Jul 2005 22:24:48 -0400, Spehro Pefhany
    <> wrote:

    ><snip>
    >Aside from series vs. shunt, some ADCs are quite demanding as far as
    >the reference output impedance goes.
    ><snip>


    I wanted to emphasize this. I've had to follow a reference with an
    op-amp.

    Jon
    Jonathan Kirwan, Jul 11, 2005
    #9
  10. Guy Macon <http://www.guymacon.com/> wrote in
    news::

    >
    >
    >
    > Michael Noone wrote:
    >
    >>Hi - I need a 4.096 voltage reference for an ADC. I'd like it to be as
    >>accurate as possible, naturally. I've been looking at the various
    >>4.096 voltage references (Maxim alone makes about 45) - and I've
    >>noticed that they for the most part can be grouped as either shunt or
    >>as series voltage references. From what I can tell a shunt V reference
    >>is just a zener diode of the rated voltage. A series V reference is
    >>just a voltage regulator. Is this right? Does one have a major
    >>advantage over the other? Thanks for your help!

    >
    > Look here:
    > Understanding Voltage-Reference Topologies and Specifications
    > [ http://pdfserv.maxim-ic.com/en/an/AN719.pdf ]
    >


    Thanks - that was very helpful. I had been looking for something like that
    and just couldn't find it for some odd reason.

    -Michael
    Michael Noone, Jul 11, 2005
    #10
  11. Michael Noone

    Robert Baer Guest

    Michael Noone wrote:
    > Robert Baer <> wrote in
    > news:NeqAe.6294$:
    >
    >
    >> I strongly suggest you look for *any* other brand; Maxim has the
    >> bad
    >>habit of advertising vaporware.

    >
    >
    > Do you mean that they advertise alot of products that they never bring to
    > market? I noticed they had a couple really nice SOT-23 V-regs - and then I
    > realized that I couldn't find a distributor for *any* of the accurate ones.
    > I also noticed they don't have samples available for these parts - so it
    > seems to me that any parts that they have samples available for
    > available... Thus I was lookin at the Maxim MAX6126:
    >
    > http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3623
    >
    > .06% initial accuracy and it comes in a 8-uMAX package. (it says .02% on
    > the above page but the 4.096 8-uMAX part is .06% if you look at pg. 16 of
    > its datasheet) It does need a couple external components though (some small
    > capacitors). It also seems to be available as a sample - though I couldn't
    > find any distributor that stocked it. This is not a big deal as a total of
    > 6 of these units will be made. I have made a sample request of this part -
    > I guess I'll have to see if it actually comes.
    >
    > Does that look like a good choice?
    >
    > -Michael

    If you do not mind waiting for a long time or possibly forever...
    Robert Baer, Jul 12, 2005
    #11
  12. Michael Noone

    PeteS Guest

    Maxim does not have the best reputation for delivering on their
    'products', especially in their reference stuff.

    Even though they have claimed to me in the past that they have 'changed
    their ways' and will ship even if you don't want to buy 100k units of
    something, I have found their delivery very spotty. That can be a big
    problem if your system fundamentally relied on the function of the
    device you want from them, and they blithely quote 8-14 weeks lead
    time, when their reps etc. have promised there is sufficient stock on
    hand for the build you wanted to schedule in 3 weeks.

    I always try and find an alternative (or multiply sourced) part when I
    see Maxim on the datasheet / suggested list.

    Cheers

    PeteS
    PeteS, Jul 12, 2005
    #12
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