The MF-PID option consists of 4 configurable PID (proportional – integral – derivative) controllers. Seamlessly integrated with the MFLI 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 with PLL capability
- PID Advisor (for adjustment of target bandwidth)
- Auto Tune PID (for minimization of average PID error signal)
- 50 kHz maximum loop filter bandwidth
- Phase unwrap for demodulator phase data (± 1024 π)
- Low-pass filter for derivative branch
MF-PID upgrade and compatibility
- Field-upgradeable option without the need for hardware changes
- Compatible with all other MF options
- Laser frequency stabilization
- Fiber noise cancellation
- Optical phase-locked loops, e.g. carrier envelope offset stabilization (CEO)
- Advanced AFM modes, e.g. Kelvin probe force microscopy and tip protection
- MEMS characterization
One important application of PID controllers is the phase-coherent synchronization of two oscillators. In the simplest case, a modulated signal is sent to the lock-in amplifier and the PLL is used to recover and track the frequency of the signal. 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 optional phase unwrapping in PLL mode extends the input range to ±1024π, ensuring a reliable feedback at the start-up and robust operation throughout.
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 manually or automatically in toggle mode; 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.
AFM tip protection with the Threshold Unit
The MF Threshold Unit can be used in combination with the PID controllers. In addition to tracking demodulator amplitude and phase values, it is possible to monitor PID errors, PID shifts, and PID output signals with the Threshold Unit. Whenever any of these signals leaves the adjustable safety corridors for a defined temporal interval, logical outputs can be generated to take action and avoid damage on the setup. Tip protection in AFM applications is a typical example where this functionality is used successfully.
|Configuration||4 PID controllers with PLL capability|
|PID input parameters||X, Y, R, and Theta from demodulator, auxiliary inputs 1 and 2, auxiliary outputs 1 to 4|
|PID output parameters||Amplitude of signal outputs, signal output offset, internal oscillator frequencies, auxiliary outputs 1 to 4, demodulator phase offsets|
|Maximum PID bandwidth||up to 50 kHz|
|PID minimum propagation delay||2.5 µs (Signal Input to Signal Output)|
|PID Advisor DUT models||All pass, low pass 1st order, low pass 2nd order, VCO/laser setup, resonator frequency, resonator amplitude, internal PLL|
|PID Advisor graphical display options||Bode magnitude, Bode phase, step-response, impulse-response; closed loop and open loop|
|Setpoint toggle rate||64 mHz to 1 MHz|
|PID data streaming||PID error, PID shift and PID output values can be streamed at an adjustable rate, synchronized with demodulator data|
|PLL frequency range||1 to 500 kHz; 1 to 5 MHz, requires MF-F5M option|
|PLL bandwidth||Up to 50 kHz|
|Phase unwrap range||±1024 π|