op-amp schematic analysis

Discussion in 'General Electronics Chat' started by eng_alaakaa, Sep 28, 2011.

  1. eng_alaakaa

    Thread Starter New Member

    Sep 21, 2011
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    Hi all,
    my graduation project about RFID , and this schematic is concern reader, my problem is the function of every op-amp that concern the receiver part of the reader.......... the picture is attached with my post.
    and thank you all:).
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    1 - Voltage follower
    2 - Inverting amplifier
    3 - High pass active filter
    4 - Inverting amplifier
    5 - Comparator with hysteresis
     
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  3. SgtWookie

    Expert

    Jul 17, 2007
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  4. colinb

    Active Member

    Jun 15, 2011
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    The Microchip schematic shows the LM339MA op-amp with inputs floating. Is that a Bad Thing? I remember reading that unused op-amps should be not have their inputs left unconnected (e.g., configure as voltage follower).
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    LM339's are comparators that have open collector outputs.
    The unused inputs should be grounded. The unused outputs can be left disconnected.
     
  6. colinb

    Active Member

    Jun 15, 2011
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    Has anyone else thought that op-amps and comparators should have different schematic symbols?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Well, they actually have a lot of similarities - it's just that they are optimized for their particular functions.

    In a limited way, you can use one for the other - at low speeds, and if you don't really care about optimal response.

    You'll quite frequently see schematics where someone used 3 of a quad opamp as opamps, and the remaining one as a comparator - or something similar.

    A new member posted a schematic of a PWM circuit, and wanted an explanation of how it worked. It used two channels from an LM324; one as an opamp to create a triangle wave, and the other as a comparator. They could have just as well used an LM393 dual comparator. National actually markets an IC that has an opamp for one channel, and a comparator for the other; that would be a good device to use for such circuits.
    The LM392 opamp/comparator:
    http://www.national.com/ds/LM/LM392.pdf
    The opamp is like a channel from an LM158/LM358.
    The comparator is like a channel from an LM193/LM393.
     
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