RF Power Detector


All RF devices and equipment must carefully monitor and control their transmit power in order to comply with wireless communication standards and minimize RF interference with other radio devices. RF power detectors are used to measure power of RF signals in transmit/receive chains in wireless communication systems. A RF power detector produces DC output voltage proportional to the RF signal power at the input of detector.

Classification

RF power detectors are broadly classified into two categories

  1. Logarithmic type : The DC output voltage is proportional to the log of RF power of the input signal
    Eg.: For power measurement and control applications
  2. RMS type : The DC output voltage is proportional to RMS value of the input signal
    Eg: For high PAPR signals such OFDM signals in WiMaX, WCDMA standards

The choice of RF detector depends on the type of the RF signal and application

Applications

  • Tx side : power measurement(to comply with standards) and power control
  • Tx/Rx gain control
  • RSSI in receivers
  • Envelope detection in envelope tracking PAs
  • Voltage standing wave ratio (VSWR) measurement and control at PA and antenna interface

Performance metrics

The performance of RF power detector is evaluated based on the following metrics

  • Linearity
  • Dynamic range
  • Temperature stability
  • Ease of use and calibration
  • Frequency range
  • Form factor

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