UHF-PID Quad PID/PLL Controller

The UHF-PID option consists of 4 configurable PID (proportional - integral - derivative) controllers. Based on a variety of different measurement data they can provide fast feedback to a number of instrument parameters and output values. Seamlessly integrated with the lock-in amplifier, the programmable PIDs enable operation in a wide range of applications such as the setup of PLLs (phase-locked loops) for phase synchronization of two lasers, CEO stabilization and fast AFM modes. The PID Advisor helps to quickly find suitable parameters and displays step responses and transfer functions to support in depth understanding of the setup. With the Auto Tune feature the loop filter settings are automatically adjusted to find the point with minimal residual PID error.

UHF-PID Key Features

  • 4 independent PID controllers
  • PID Advisor with multiple DUT models, transfer function and step function modeling to achieve an adjustable target bandwidth
  • Auto Tune PID that automatically minimizes the average PID error signal by adjusting various set of parameters and bandwidth
  • High speed operation with up to 300 kHz loop filter bandwidth
  • Input parameters: demodulator data, auxiliary inputs, auxiliary outputs and arithmetic unit
  • Output parameters: Output Amplitudes, Oscillator frequencies, Demodulator Phase, Auxiliary Outputs and Signal Output Offsets
  • Phase unwrap for demodulator Θ data (± 1024 π), e.g. for optical phase locked loops
  • Low pass filter for derivative branch

UHF-PID Upgrade and Compatibility

  • Option upgradeable in the field
  • Compatible to all other UHF options

UHF-PID Applications

  • Laser frequency stabilization
  • Optical Phase locked loop, e.g. carrier envelope offset stabilization (CEO)
  • High-speed AFM, e.g. automatic gain control (AGC)
  • MEMS measurements, e.g. gyroscopes
  • Interferometer stabilization
  • Nano-mechanical oscillators

UHF-PID Functional Diagram

Phase Locked Loop

One important application of the PID controllers is the phase coherent synchronization of two oscillators - Phase Locked Loop or PLL. The most simple case is whenever a signal is provided to the lock-in amplifier as an external frequency reference and then automatically mapped to one of the internal oscillators by setting either demodulator 4 or 8 to ExtRef. One PID would then take the phase information from one of the demodulators as an input and provide feedback to the frequency of one of the internal oscillators. It is important to know that this principle can also be reversed and the good phase noise properties of the internal oscillators can for example be transferred to an external setup such as a laser system.

Arithmetic Unit

The Arithmetic Unit can be used in combination with the PID controllers and allows to perform basic mathematical operations for instance on demodulator data before providing the result as input for the PID. A simple example is the stabilization of an interferometer where the calculation of a phase angle based on atan2(Y/X), where the X component is taken from the fundamental frequency and the Y component of the 2nd harmonic multiplied with a normalization factor, can be used for feedback.

PID Advisor and Auto Tune

While the PID Advisor and the Auto Tune feature allow for easy and convenient setup of control loops even for the inexperienced user, the LabOne toolset provides all means to characterize the achieved performance. The Plotter visualizes PID error and PID output in the time domain and shows a histogram for the data, the SW Trigger can be used to record step responses when the PID set point is changed. These step responses can directly be compared to the model functions of the PID Advisor. The integrated Spectrum Analyzer displays the frequency domain data of the control loop signals to see "servo bumbs" and potential noise sources and the Sweeper allows to characterize transfer functions to gather a thorough understanding of the entire setup.

UHF-PID Specifications

Configuration 4 PID controllers with PLL capability
PID input parameters X, Y, R, and Theta from demodulators 1 to 8, auxiliary inputs 1 and 2, auxiliary outputs 1 to 4
PID output parameters Amplitude of signal outputs 1 and 2, signal output offsets, frequency of oscillators 1 to 8, auxiliary outputs 1 to 4
PID bandwidth up to 300 kHz
PID minimum propagation delay 1.5 µs (Signal Input to Signal Output)
PLL frequency range 10 Hz - 600 MHz
PLL bandwidth up to 300 kHz

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