communication ckts using OTAs

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

  1. Lubna

    Thread Starter New Member

    May 5, 2013
    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


    Oct 2, 2009
    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
    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
    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.