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Digital Lock-in amplifier pulls signal out of noise floor

*NEW*
Completely new design of lock-in firmware available.
Supports multiple references, both external and internal complex references.
Sample Rate SR up to 2 MSPS using new modular product range
Up to 32 channels per unit and configurable 4 or more references typical.
New design uses a high-order FIR to decouple REF frequency from SR.
Complex reference is insensitive to phase error.
example complex spectrum of lock-in signal, compared to raw signal in time domain showing 4 REF with varying mix-down frequency typical ACQ1001 appliance
Please contact D-TACQ for details. email: info@d-tacq.co.uk

Special DSP firmware allows ACQ196CPCI to function as a 96-channel digital lock-in amplifier.
This is a digital integrator that will yield huge processing gain when an incoming signal is correlated with a reference signal.
lock-in amplifier definition [Wikipedia]

The D-TACQ implementation is somewhat unique in that there are many simultaneous channels. The standard implementation uses a single reference
(either a single analog input channel, or internal reference). The logic is capable of generating a stimulus waveform to the plant, and the reference may be either the digital representation of this exact waveform, or any other digital waveform defined in a lookup-table.

There are several implementations of the logic:

96 Channels, single reference
32 Channels, 4 references
96 Channels, multiple references {1, 3 or 5}.

In addition, the FPGA logic can include a downstream FIR LP filter.

Typical applications include

  • Array magnetometer using in medical imaging
  • Digitizing output of Photo Elastic Multiplier in Motional Starck Effect diagnostic
  • Digital integrator for long term magnetics monitoring with low drift.

Example


Test using a small signal. The lock-in is able to extract a DC value corresponding to the signal;
In the presence of intense noise, the small signal is invisble in the noise floor, however the lock-in is still able to resolve it as before.
The signal would benefit from some additional LP filtering, this can easily be done in software, since the output data rate is low.

FFT without lock-in Lock-in output
Without Noise Small signal, no noise, no processing Small signal, after lock-in processing
With Noise Small signal, intense noise, no processing Small signal, intense noise, after lock-in processing