communication ckts using OTAs

Discussion in 'Wireless & RF Design' started by Lubna, Jun 13, 2013.

  1. Lubna

    Thread Starter New Member

    May 5, 2013
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    I recently read in a journal that the compander and the adaptive delta modulator circuit could be implemented through OTAs. it was mentioned that the value of step size and µ ( they were using a µ law compander circuit) could be varied by varying the transconductance of the otas used. how are these parameters varied in conventional compander and delta modulator ckts? I want to know the advantage of using otas for these ckts.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,414
    3,353
    I don't know what OTA means.

    So I had to do a search.

    OTA stands for Operational Transconductance Amplifier.

    Now I know.
     
  3. Lubna

    Thread Starter New Member

    May 5, 2013
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    0
    sorry I did not elaborate upon OTA. it is a voltage controlled current source whose transconductance can be varied through an external bias current. it is a low power device so it can be used in micro power applications. I just want to know that how are the values of step size and
    µ controlled in conventional delta modulator and compander circuits so that I can understand the purpose of using OTAs for implementing these ckts.
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,039
    287
    An OTA is ideal for doing this....though there are newer methods. By a simple DC control voltage, you can control the gain over a very wide range. The key to A law and U-law implementation is how you derive the FEEDBACK to control the DC voltage

    A typical compressor would rectify a small sample of the output signal and apply this to the gain control of the OTA. The matching expander would use the same method, but with a simple polarity reversal of the feedback voltage.

    Eric
     
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