Open Source SPM Controller & PLL
Model Mk3-PLL

The Open Source SPM Controller & PLL can be used as:
ü a SPM controller
ü a controller with an embedded PLL, orü a stand alone PLLThis MK3-PLL model is fully compatible with the SPM control softwaredeveloped by the GXSM Group. This model has more computational power andmemory than the MK2-A810 model for further developments and improvementsof the next generation of the GXSM control code.
One of the great innovation of this model is an embedded PLL function.

“Ultrathin Bi(111) film ona Si(111)-7x7 substrateImages provided by, C.A. Bobisch,M.C. Cottin, J. Schaffert and R. Möller”

Key Features of the PLL ModuleThis highly optimized software PLL module is based on an innovative
phase/amplitude detector. This module is embedded in the SPM controller
firmware code.

“Si(111)-7x7 reconstruction
Image provided by, D.v.Vörden,M.Lange and R. Möller”“Schematic Diagramof the PLL”

The analog I/O board of this SPM controller Mk3-PLL model also includes a TCXO (temperature compensated crystaloscillator), which greatly improves the PLL’s thermal stability and reduces its noise at low frequencies.

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Key Features of the PLL Module• The PLL module is based on an innovative (patent-pending) phase/amplitude measurement technique. This technique does
not rely on narrow-band filtering like traditional demodulation techniques. The result is signal capture and tracking capabilities
that encompass the whole frequency range, with better noise and precision/time-constant trade-offs that are independentof frequency range.
• Allows the control of both the phase and amplitude of the resonator signal.
• Implemented as a module of the SPM controller’s firmware. This way, high resolution input and output signals are directly
accessible in digital form. No DAC/ADC conversions take place between the PLL and SPM controller, as is the case witha stand-alone PLL. This provides greater precision and lower group-delay for a faster loop response.
• Includes a function to automatically measure the resonator-frequency response and characteristics:
ü Frequency and phase at resonanceü Q factor
ü Gain at resonance• Includes a special auto-set feature to simplify the loop-gain set-up. With the auto-set feature, the user only needs to specify
the desired closed-loop response for both controllers. The module automatically sets the loop gains to achieve the desiredresponse.
• Includes a unique step-response function that allows the in-circuit measurement of the closed-loop response for both thephase and amplitude loops.
• The PLL module generates the excitation frequency, the excitation amplitude, the resonator phase and amplitude signals.
• Both phase and amplitude loops have an additional output low-pass filter to reduce the noise on all PLL signals.
This filter is automatically adjusted to reduce noise without altering controller bandwidth.
• The PLL module includes a function for long-term analysis of PLL signals. This can be used to assess thermal drift
and low frequency noise.

Stand-Alone PLL
The SPM controller Mk3 unit can also be used as a stand-alone PLL. Soft dB provides an open source
Windows/LabVIEW-based interface to run the SPM controller Mk3 unit as a stand-alone PLL with four output signals:

ü Excitation frequency

ü Excitation amplitude

ü Resonator phaseü Resonator amplitude“PLL stand-aloneuser-interface”

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Open Source SPM Controller & PLL
Model Mk3-PLL

PLL MODULE SPECIFICATIONS
Input Range± 10 V

Output Range± 10 V (external 1/100 and 1/1000 attenuators provided)

Frequency Range

3.2 kHz to 75 kHz

Resonator Test Board

An active resonator board is included with the SPM controller for easy testing and setup of the PLL module

PLL Output Signal Ranges(Stand-Alone Operation)

Excitation Frequency
Excitation Amplitude
Resonator Phase
Resonator Amplitude± 2.85 mHz± 1.19 μV± 6.83 μ degree± 1.19 μV

to ± 23.9 kHz
to ± 10 V
to ± 57.3 degree
to ± 10 V

Phase Controller
Bandwidth: 1 kHz

Phase Controller
Bandwidth: 5 Hz

60 mHz RMS
4 m degree RMS

20 μHz RMS
200 μ degree RMS

Amplitude Controller
Bandwidth: 7.5 Hz

Amplitude Controller
Bandwidth: 1.5 Hz

Excitation Amplitude

400 μV RMS

50 μV RMS

Resonator Amplitude

5 μV RMS

2 μV RMS

Excitation Frequency
PLL Signal Noise Levels*

Resonator Phase

Phase/Amplitude (PAC)
Detector Bandwidth

100Hz to 10kHz. The bandwidth is automatically adjusted when the loop auto-set function is used

Software Features• Resonator frequency sweep for automatic measurement of resonator frequency characteristics• Loop-gain auto-set for amplitude and phase controllers. Gains are set according to desired
closed-loop bandwidth• In-circuit closed-loop step response measurement function validates the setup of both controllers• Adjustable low-pass filter on PLL signals: Excitation amplitude/frequency and Resonatorphase /amplitude. These filters can be adjusted from 1.5 Hz to 16 kHz or bypassed.
• R eal time monitoring of all PLL signals• L ong term monitoring of PLL signals to assess the low frequency stability and noiseTemperature Coefficient• T
 CXO Stability• T
 CXO Precision

140 ppb over a temperature range from -20 °C to 70 °C
2 ppm* Note: Noise levels are measured using the resonator board included with the SPM controller (gain –13 dB at the resonance) and the auto-setof loop gains for both controllers. The new PLL technique ensures that the noise levels are independent of measurement ranges.

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