Self-balancing drift-free, high-frequency phase detector circuit


A phase detector (PD) is a circuit that compares the phases of an oscillation with a referential oscillation that has been defined in the phase. With phase detectors, time units and frequencies can be measured.

Fields of application

The new technology opens up a wide field of application:

  • in high-precision PLL circuits
  • for long-term stable continuous phase measurement of RF signals in the 10 fs-100 fs range (peak to peak)
  • for long-term stable frequency distribution
  • in optical metrology (highly precise measurement of time and reflectometry)
  • in the generation of stable frequencies for radar systems and applications
  • generally, in the metrology and communication technology with extremely high requirements for low noise and nearly drift-free phase detectors


PLLs are currently state of the art and are available as an IC component on the market. Previously, low noise in PLLs could only be achieved by a reduction in the freedom from drift or vice versa. Existing detector systems are subject to temperature-dependent drift of several pico-seconds. Concerning the drift and noise characteristics, the currently available phase detectors do not meet the high demands of the synchronisation in the femto-second range for the subcomponents of a particle accelerator for free-electron laser (FEL) and especially not for X-ray laser (XFEL), for example.
This patented technical advancement is now also available to other high technology industrial applications.


A combined detector, consisting of a self-balancing, nearly drift-free and a low noise phase detector, has been combined in order to meet the drift and noise demands.
The actual self-balancing nearly drift-free PD is optimized using a power splitter by introducing a zero balance during a calibration phase. Here, the phase drifts and low frequency 1/f-phase noise components of the reference generator, of the phase detector, of the leads and of the amplifier are being suppressed within the calibration loop. In case of different frequencies for the comparison, the matching principle can be extended in order to suppress the drift and 1/f-noise of HF splitters.


Phase detectors in PLLs (Phase Locked Loop) are being used for measuring and synchronising high frequency signals.


  • low-noise, self-balancing and nearly drift-free RF phase detector circuit
  • self-calibrating properties
  • reduction of the temperature-dependent long-term drift to 10-100 femto-second (peak-to-peak)