DXA-003 Lock-in Amplifier

DXA-003 Lock-in Amplifier

Input signal channel

The low-noise analog front-end amplifier used in the lock-in amplifier DXA-003 can effectively process single-ended or differential signals, and its equivalent input noise is 6nV/√Hz@100kHz. The input impedance of this channel is 50Ω or 10MΩ, and the input signal level that can be detected at full scale output is 1nV to 1V. The dynamic range of DXA-003 can reach more than 120dB, and it can adjust the internal programmable gain amplifier according to the amplitude of the input signal to change the dynamic reserve of the whole system. The sampling rate of the high-precision 14-bit ADC is 250MSPS, and the anti-aliasing filter in front of the ADC can effectively prevent signal aliasing.

 

Reference signal channel

The reference signal of DXA-003 digital lock-in amplifier can choose sine wave signal or square wave signal according to the actual situation of the user, and can also use the reference signal synthesized by digital inside the instrument. When the DXA-003 is set to the internal reference signal mode, the high-precision oscillator and digital synthesis algorithm inside the instrument can generate a sine wave signal for multiplying the input signal, and the internal reference signal at this time is hardly affected by phase noise. Impact. Using digital phase shifting technology, the phase of the internal reference signal can achieve a resolution accuracy of 0.001°. The instrument's internal reference signal mode can operate normally in the frequency range of 1mHz to 10 MHz. In addition, DXA-003 can also use external reference signal mode, sine wave signal and TTL logic level can be used as external reference signal. The rising or falling edge of the external reference signal triggers the internal phase-locked loop (PLL). Based on the frequency of the reference signal, the DXA-003 can detect the signal harmonics. The maximum harmonic signal frequency it can detect is 32767 times the fundamental frequency, but the maximum harmonic frequency cannot exceed the instrument’s highest measurement frequency of 10 MHz.

Digital Modulators and Output Filters

The core component of the DXA-003 is the modulator. Compared with the analog signal multiplier, the digital modulator inside this instrument can effectively suppress the potential measurement error caused by DC offset and offset. At the same time, by optimizing the multiplication operation of the coherent signal inside the digital modulator, the calculation error is minimized, so that the instrument can accurately detect the weak signal input. The time constant of the DXA-003 can be set from 10ns to 4.4ks. The roll-off rate of the output low-pass filter can be set to 6, 12, 18, 24, 32, 36, 42, and 48dB/octave. This low-pass digital filter is implemented using an infinite impulse response (IIR) filter structure with a signal processing sample rate of 250 MHz. The digital modulation method and filter structure adopted by DXA-003 ensure that it has higher dynamic reserve (>120dB), accurate phase (absolute phase error <1°), zero DC drift and good orthogonality. In addition, when the frequency of the input signal is lower than 200 Hz, the DXA-003 can turn on the synchronous filter to eliminate the harmonic influence of the reference signal, ensuring that the instrument can quickly detect effective low-frequency signals.

 

Oscillator

The lock-in amplifier DXA-003 internal oscillator can provide the instrument with a low-distortion (–80dBc) reference signal. The frequency of the single sine wave reference signal can be varied from 1mHz to 10MHz, and the frequency resolution of the generated reference signal can reach 1mHz. Using the DXA-003's front panel or computer communication, the frequency and amplitude of the reference signal generated by the internal oscillator can be set. When the instrument selects the external reference signal mode, the signal generated by the internal oscillator and the external reference signal maintain a phase-locked relationship.

Signal generator

Based on a 16-bit digital-to-analog converter (DAC), DXA-003 can generate a sine wave signal with a frequency range of 1mHz to 10MHz. Its signal frequency is related to the oscillator inside the instrument and can be set through the instrument's control catalog. The amplitude of the sinusoidal signal produced by the instrument. The maximum amplitude of the sine wave signal that the signal generator of DXA-003 can generate is 1Vrms, and the resolution is 1uVrms.

 

Display function

The 5.6-inch TFT color screen with a resolution of 640×480 is used as the main display screen of the instrument for DXA-003. The data that can be detected by this lock-in amplifier, such as X value, Y value, R value, and θ value of the signal, can be displayed in numerical value and bar graph display at the same time.

 

Manual operation

While displaying the test data, the TFT LCD screen is also used to display the control list of the instrument. Combined with the soft keys around the main screen of the instrument and the numerical keyboard on the front panel of the instrument, the user can effectively adjust the working parameters of the instrument, such as: input signal measurement mode, reference mode, frequency of internal oscillator, output amplitude of sinusoidal signal, and interface display.

Automatic function

The digital lock-in amplifier DXA-003 can automatically adjust the working parameters of the instrument to obtain the optimal measurement mode required for different input signals. Using the independent different buttons in the instrument's control menu, the user can reasonably adjust the overall gain of the instrument, the phase of the internal reference signal, the dynamic reserve and the display ratio of the instrument. Based on the automatic adjustment function, the instrument can automatically and easily measure the input signal to be tested.

 

PC software operation

         DXA-003 has three interfaces: RS232, USB2.0 and Ethernet, which can set all the functions of the instrument to ensure that users can effectively use all the test functions of DXA-003 on the control computer, including setting the reasonable control parameters of the instrument and Read the data measured by the instrument. At the same time, in order to allow users to use various functions more conveniently, this instrument is equipped with a corresponding LabVIEW program, which can read and save the measured data in real time. This enables DXA-003 to be easily applied to complex scientific experiments.