60MHz Digital Lock-in Amplifier

With the low-noise analog pre-amplifier, the signal input of DXA-004 can be switched to operate in the single-ended or differential voltage mode, and the input noise is 6 nV/√Hz@100 kHz. The input impedance is 50 Ω or 10 MΩ and the full-scale input voltage sensitivity ranges from 1 nV to 1V. Two line filters (50/60 Hz and 100/120 Hz) are designed to eliminate line related interference. The programmable gain amplifier is provided to adjust the dynamic reserve of the system according to the magnitude of the input signal, so that DXA-004 has an inherently large dynamic reserve up to 120dB. The sampling rate of 250MSPS is determined by a precision 14-bit A/D converter and a specific filter is designed to avoid aliasing.

In order to provide the reference signal for DXA-004, an externally applied sine wave or square wave, or its own internally synthesized reference source could be used. When the instrument is set to internal reference mode, the internal precision stabilized oscillator and the digital synthesized algorithm are used to generate sinewave output that multiplies the input signal, there is virtually no reference phase noise when choosing internal reference mode. Taking advantage of the digital phase-shifting technique, the reference signal phase could be adjusted with 0.001° resolution. The internal reference mode can operate at a fixed frequency from 1 mHz to 60 MHz. In addition, the external reference is also applicable to DXA-004, including the sinewave reference signal and TTL logic reference signal. The rising and trailing edge of the external reference signal are applied to trigger off the internal Phase Locking Loop (PLL). Based on the frequency of the reference signal, harmonic detection can be performed by DXA-004. The maximum frequency of the measurable harmonics is 32767 times of basic frequency, and it is also less than the maximum operational frequency 60 MHz.

The key component of the DXA-004 is the digital demodulator. Compared to traditional analog lock-in amplifiers, the DXA-004's internal digital demodulator effectively rejects the measurement errors caused by DC drift and offset. In addition, by optimizing the multiplication of the internal coherent signal of the digital demodulator, the calculation error is minimized so that the instrument can accurately detect the input weak signal. Time constants of the output low-pass filter from 30 ns to 4.4 ks can be selected with a choice of 6,12, 18, 24, 30, 36, 42 and 48 dB/oct roll off. This low-pass digital filter is implemented using a high performance digital filter with a sample rate of 250 MHz. The digital demodulation and the low-pass filter used in DXA-004 guarantee a high dynamic reserve (>120dB), and accurate phase (absolute phase error <1 deg). Moreover, when the frequency of the input signal is lower than 200 Hz, A synchronous filter can be used to eliminate the harmonic influence of the reference signal, ensuring that DXA-004 can detect a low frequency signal quickly and effectively.

DXA-004 has a 5.6-inch 640 x 480 color TFT-LCD. The measurement results of DXA-004, such as X, Y, R, and θ, are shown in numerical form and bar graph on the display. In X-Y chart, DXA-004 shows the trend of measurement results over time, and checks the value by using a knob control cursor.

Users can use a PC to control DXA-004 through communication interfaces, including setting the parameters and reading the measurement data. DXA-004 is equipped with a free LabVIEW program, which makes it easy to use in complex scientific experiments.

USB2.0 , RS-232(DB-9) and 1000Mbps Enthernet

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1. What is a lock-in amplifier?

Answer: A lock-in amplifier is a precise electronic instrument used to measure and amplify specific frequency components in a signal. By phase-locking with the input signal, it can accurately extract weak signals buried in noise background. Lock-in amplifiers are commonly used in experimental research and precise measurements in fields such as optics, electronics, and magnetism.

2. How does a lock-in amplifier work?

Answer: The basic principle of a lock-in amplifier is to phase-synchronously lock the signal to be measured with a reference signal, and after filtering, amplification, etc., it outputs a signal in which both amplitude and phase information have been measured. This method effectively extracts weak signals, suppresses background noise, and improves measurement sensitivity and accuracy.

3. What are the application areas of lock-in amplifiers?

Answer: Lock-in amplifiers are widely used in scientific research, industrial production, and precision instrumentation fields. In optical experiments, lock-in amplifiers are used to measure optical interference, optical scattering, and other phenomena; in the electronics field, they are used to detect weak signals and noise interference; in the biomedical field, they are used for control and monitoring of treatment devices, and so on. In general, lock-in amplifiers play an important role in improving signal measurement accuracy and noise suppression.