The UHF-PID option consists of 4 configurable PID (proportional – integral – derivative) controllers. Seamlessly integrated with the UHFLI Lock-in Amplifier, the programmable PIDs feature in several applications including the setup of phase-locked loops (PLLs) for phase synchronization of two lasers, CEO stabilization, and fast AFM modes. The PID Advisor helps to identify suitable parameters, and displays step responses and transfer functions to support in-depth understanding of the experimental setup. Thanks to the Auto Tune feature, the loop filter settings are automatically adjusted to find the point with minimal residual PID error.
Quad PID/PLL Controller Option
- 4 independent PID controllers
- PID Advisor (for adjustment of target bandwidth)
- Auto Tune PID (for minimization of average PID error signal)
- High-speed operation with up to 300 kHz loop filter bandwidth
- Input parameters including demodulator data, auxiliary inputs, auxiliary outputs, and Arithmetic Unit
- Output parameters including output amplitudes, oscillator frequencies, demodulator phase, auxiliary outputs, and signal output offsets
- Phase unwrap for demodulator phase data (± 1024 π), e.g. for optical PLLs
- Low-pass filter for derivative branch
UHF-PID upgrade and compatibility
- Field-upgradeable option
- Compatible with all other UHF options
- Laser frequency stabilization
- Interferometer stabilization
- Optical phase-locked loops, e.g. carrier envelope offset stabilization (CEO)
- High-speed AFM, e.g. automatic gain control (AGC)
- MEMS characterization
One important application of PID controllers is the phase-coherent synchronization of two oscillators. The simplest case is that of a signal provided to the lock-in amplifier as an external frequency reference and then automatically mapped onto one of the internal oscillators by setting either demodulator 4 or 8 to ExtRef. One PID takes the phase information from one of the demodulators as the input and provides feedback to the frequency setting of one of the internal oscillators. Importantly, this principle of operation can be reversed so that the good phase noise properties of the internal oscillators can be transferred onto an external laser system, for example.
The Arithmetic Unit can be used in combination with the PID controllers to perform basic mathematical operations on demodulator data, for instance, before providing the result as an 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) (with the X component 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 make the setup of control loops straightforward, 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 data histogram, whereas the SW Trigger can be used to record step responses when the PID setpoint is changed; these step responses can be directly compared to the model functions of the PID Advisor. The integrated Spectrum Analyzer displays frequency-domain data to highlight "servo bumps" and identify potential noise sources. The Sweeper tool helps to study transfer functions to gather a more thorough understanding of the entire experimental setup.
|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|