impedance matching for reactive loads

Discussion in 'General Electronics Chat' started by MiG, Jun 15, 2010.

  1. MiG

    Thread Starter New Member

    Mar 13, 2009
    hi guys,

    Got an issue with a power amplifier, it is delivering it's power to a Surface Acoustic Wave (SAW) device. I'm not sure how to handle the impedance matching required at the output of the amp and the input of the Saw transducer given that the load is purely capacitive at resonance, where I expect the device to operate.

    Thus, how do you handle the design of a impedance mathcing network where the source is resistive and the load is purely reactive with no real part to it's impedance?

    any help greatly appreciated.
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    If the SAW device is absorbing power (which is then delivered to the medium in which the SAW device is immersed, be it air or something else), then its impedance will have a real part.

    That real part of its impedance may be difficult to measure if the Q of the device is high, but it will have a real part.
  3. Papabravo


    Feb 24, 2006
    Do you have access to a VNA? That's a vector network analyzer. If not then your problem has no practical solution. To buy they are north of $100K, but you can rent them for a short period of time if your wallet allows.

    This way you can characterize the device and the amplifier. Once you can see the behavior of source and load you can do the complex conjugate match.

    Typical data-sheets seldom have enough information to do this by hand.
  4. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    What is your operating frequency?
  5. sweaterlife

    New Member

    Mar 24, 2010
    Hi, just bumping this to see how you solved your problem, MiG?

    I'm currently working with SAW transducers, however I have access to a very nice Agilent network analyser, which can produce smith charts on the fly for me and make it easy to match the impedance for a specific frequency. I'm using various combinations of RC networks, depending on whether the load is inductive or capacitive at a certain frequency.

    However as we sometimes need to drive the transducers at a couple of frequencies, I'm wondering if anyone has any advice on building a wideband or even an active tuning network?

    Any help is much appreciated!