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](images/lock-in-example-opi.png) |
![showing 4 REF with varying mix-down frequency](images/lock-in-multiple-refs.png) |
![typical ACQ1001 appliance](images/acq1001-acq435-oblique.jpg) |
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](images/lock-in/acq196LockIn-SmallSig.1.31fft.png) |
![Small signal, after lock-in processing](images/lock-in/ACQ196_LockIn_63_Tap_Filter.png) |
With Noise |
![Small signal, intense noise, no processing](images/lock-in/acq196LockIn-SmallSig+Noise.1.31fft.png) |
![Small signal, intense noise, after lock-in processing](images/lock-in/ACQ196_LockIn_63_Tap_Filter+Noise.png) |