DXA-004 60MHz Digital Lock-in Amplifier
Input Channel
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.
Reference Channel
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.
Digital Demodulator and Output Filter
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.
Display
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.
Remote Operation
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.
Signal Channel
Voltage input Mode Single-ended or Differential
Full-scale Sensitivity 1 nV to 1 V in a 1-2-5 sequence
Impedance
Voltage 50 Ω // 5pF or 10 MΩ // 5pF,AC or DC coupled
C.M.R.R >70 dB to 100 Hz
>50 dB to 100 kHz
Dynamic reserve >120 dB
Gain accuracy 0.5% typ(<1MHz), 3% max
Voltage Noise
14 nV/√Hz at 997 Hz
6nV/√Hz at 99.99 kHz
Line filters 50/60 Hz and 100/120 Hz
Grounding BNC shield can be grounded or floated via 10 kΩ to ground
Reference Channel
Input
Frequency range 1 mHz to 60 MHz
Reference input TTL or Sine
Input impedance 1 MΩ
Square reference level VIH>3V， VIL<0.5V
Sine reference signal >1 Hz
> 400 mVpp
Phase
Resolution 0.001°
Absolute phase error <1°
Relative phase error <1 mdeg
Phase noise
Internal ref. Synthesized, <0.0001 deg at1 kHz
External ref. 0.001 deg at 1 kHz (100 ms time constant, 12 dB/oct)
Drift
<0.01 deg/℃ below 100 kHz
<0.1 deg/℃ above 100 kHz
Harmonic detection 2F, 3F, …nF to 60 MHz (n<32,767)
Acquisition time
Internal Ref. Instantaneous acquisition
External Ref. (2 cycles + 5 ms) or 40 ms, whichever is larger
Demodulator
Stability
Digital outputs no zero drift on all sets
Display no zero drift on all sets
Analog outputs <5 ppm/℃ for all dynamic reserve settings
Harmonic rejection -90 dB
Time constants 30 ns to 4.4 ks (6,12,18,24,30,36,42,48 dB/oct roll off)
Synchronous filters Available below 200 Hz(18,24,30,36,42,48 dB/oct roll off)
Internal Oscillator
Frequency Range 1 mHz to 60 MHz
Accuracy 2 ppm + 10 µHz
Resolution 1 mHz
Distortion -80 dBc (f<10 kHz)，-60 dBc (f>1 MHz)
Amplitude 1uVrms to 1 Vrms ( Resolution:1 uVrms)
Accuracy 0.5%
Stability 50 ppm/℃
Sine Outputs
Sine signal， output impedance 50 Ω
TTL Outputs 5V TTL/CMOS level，output impedance 50Ω
Display
Screen 5.6 inch, 640×480 TFT
Screen format Single or dual display
Display quantities Each display shows one trace,
traces can be defined as X,Y,R,θ
Display types Numerical form, bar graph
AUX Inputs and Outputs
AUX Inputs
Function 4 Channel Inputs
Amplitude ±10 V，1 mV resolution ratio
Impedance 1 MΩ
AUX/CH Outputs
Function 4 Channel Outputs
Amplitude ±10 V，0.1 mV resolution ratio
Drive current 30mA max
Interfaces
USB2.0 , RS-232(DB-9) and 1000Mbps Enthernet
General
Power requirements
Voltage 220~240 V AC
100~120 VAC(optional)
Frequency 50/60 Hz
Power 60 W
Power supply rejection 70dB@1MHz
Weight 12 KG
Dimensions
Width 448 mm
Depth 513 mm
Height
With feet 148 mm
