The DME Lock-In Amplifier

The DME Lock-In Amplifier is a combination of the following components:

• Lock-In Amplifier with X/Y/Amplitude output
• 14 bit, 2 channel 40 MHz Digital Storage Oscilloscope
• Frequency generator with variable phase and nth harmonic generation
• Phase-Locked-Loop (PLL) for optional control of the frequency generator
• Feedback system (PI controller)
• Digital Spectrum Analyzer
• Two inputs and two outputs

Both inputs are samples with 14 bit high speed digital analog converters. All other functions are realized fully digitally (FPGA based). This results in a linearity unreached by conventional analog systems and allows arbitrary combining of the different functional groups without disadvantages in signal bandwidth and cross talk.

The user front end is realized in Java and runs on all suited operating systems as for example Windows / MAC / Linux etc. No drivers are needed, all communication runs via standard ethernet. A screen shot of the user front end can be seen here. The data curves displayed by the oscilloscope functions can be saved as a two column text file on the hard disk.

The following table gives an overview of the technical parameters

Input / Output Configuration: 2 Eingangs- und 2 Ausgangskanäle In-/Output voltage range: ±10 V Oszilloskop sampling speed range: 0,61 kHz … 40 MHz Number of data points per oscilloscope curve: 512 Spectrum analyzer frequency resolution: sampling-frequency / 1024 A/D converter dynamics: 14 bit at 40 MHz Frequency generator base frequency: 80 MHz Frequency generator frequency dynamic: 32 bit Frequency generator waveform look-up table depth: 4096 Frequency generator phase resolution: 0,088 ° Lock-In amplifier dynamics: 28 bits Lock-In amplifier filter dynamics: 54 bits PI controller integrator dynamics: 30 bits Overall noise: typ. <6 nV / √ Hz Processing units: 1 FPGA and 1 32 bit DSP Analog bandwidth: Limited to approx. 5 MHz, optionally up to 40 MHz

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