SSI Modular Lock-In Amplifier OE1311/OE1351

Overview

The OE1311/OE1351 module lock-in amplifier is our latest core-technology product: a high-performance, cost-effective measurement instrument. Built on digital modulation, output filters, and a high-precision 24-bit DAC (ADC), and employing a new Zynq architecture, it accurately and rapidly extracts valid signal components buried in large noise. The OE1311/OE1351 lock-in amplifier also measures both amplitude and phase of the input signal simultaneously, and its core specifications—measurement accuracy, operating frequency range, signal-to-noise ratio, and dynamic reserve—rival the best in the international industry. Newly developed capabilities, including multi-harmonic measurement, an oscilloscope, and a spectrum analyzer, extend the OE1311/OE1351 to a wide range of research and industrial applications.

Input Signal Channel

The low-noise analog front-end amplifier in the OE1311/OE1351 lock-in amplifier handles differential or single-ended signals effectively, with an equivalent input noise of 10 nV/√Hz. The channel's input impedance is 10 MΩ, and the detectable input signal level at full-scale output ranges from 1 nV to 5 V. In addition, the OE1311/OE1351 supports input current measurement with a variable front-end current gain of 10^6  V/A. The OE1311/OE1351 achieves a dynamic range exceeding 120 dB and adjusts its internal programmable gain amplifier according to input signal amplitude to vary the overall dynamic reserve. The high-precision 24-bit ADC samples at 4 SPS, and the anti-aliasing filter ahead of the ADC effectively prevents signal aliasing.

Reference Signal Channel

The reference signal of the OE1311/OE1351 digital lock-in amplifier can be selected as either a sine wave or a square wave according to the user's requirements, and the instrument's internally synthesized digital reference signal can also be used. When the OE1311/OE1351 is set to internal reference mode, the high-precision internal oscillator and digital synthesis algorithm generate the sine wave used for multiplication with the input signal, and this internal reference is virtually immune to phase noise. Digital phase-shifting technology allows the internal reference phase to be set with a resolution of 1 µdeg. The internal reference mode operates over a frequency range from 1 µHz to 100/500 kHz. In addition, the OE1311/OE1351 supports external reference mode, in which a sine wave or TTL logic level can serve as the external reference. The rising or falling edge of the external reference triggers the internal phase-locked loop (PLL). Based on the reference frequency, the OE1311/OE1351 can detect signal harmonics up to the 65,535th harmonic of the fundamental, provided the maximum harmonic frequency does not exceed the instrument's 100/500 kHz operating frequency.

Filters

The core component of the OE1311/OE1351 is the modulator. Compared with analog signal multipliers, the instrument's internal digital modulator effectively suppresses potential measurement errors caused by DC offset and drift. Optimized multiplication of the internal coherent signal within the digital modulator minimizes computational error, ensuring accurate detection of weak input signals. The time constant of the OE1311/OE1351 is adjustable from 1 μs to 3 ks. The output low-pass filter roll-off can be set to 6, 12, 18, 24, 30, 36, 42, or 48 dB/oct. This low-pass digital filter is implemented using an infinite impulse response (IIR) filter structure with a signal processing sampling rate of 4 MHz. The digital modulation method and filter architecture of the OE1311/OE1351 deliver higher dynamic reserve (>120 dB), accurate phase (absolute phase error <1°), zero DC drift, and excellent quadrature performance compared with analog lock-in amplifiers. In addition, when the input signal frequency is below 1 kHz, the OE1311/OE1351 engages a synchronous filter to eliminate harmonic effects from the reference signal, enabling fast detection of valid low-frequency signals.

Oscilloscope

The oscilloscope features a 4 MSa/s analog input channel with 2 MHz analog bandwidth, a 5 Vrms input voltage range, and user-configurable AC/DC coupling and 10 MΩ impedance. 

Spectrum analyzer

The spectrum analyzer observes input signals from DC to 2 MHz in the frequency domain, with resolution bandwidth down to 1 Hz and a minimum span of 100 Hz. 

Multi-Demodulator

A conventional lock-in amplifier can measure only the fundamental or a single harmonic component at any one time. When multiple frequency components must be measured simultaneously for amplitude and phase, a traditional lock-in amplifier cannot meet the requirement. The digital section of the OE1311/OE1351 combines FPGA and ARM technology to deliver higher processing bandwidth and a more flexible digital architecture, with digital processing accuracy up to 48 bits, enabling simultaneous analysis of up to 8 signal inputs at user-defined frequencies. The 8 demodulators can be freely configured for amplitude and phase, allowing flexible combinations. 

Signal Generator

Built on a 16-bit DAC, the OE1311/OE1351 generates sine waves from 1 µHz to 100/500 kHz. The amplitude and phase of the output are referenced to the instrument's internal oscillator, and the sine wave amplitude can be set through the instrument's control menu. The maximum sine wave amplitude of the OE1311/OE1351 signal generator is 5 Vrms.

Interfaces

The OE1311/OE1351 offers a 1000 Mbps RJ45 Ethernet port and an XH 2.54-4 pin serial port. Through either interface, users can access all test functions of the OE1311/OE1351 from a control computer, including setting appropriate control parameters and reading measured data.

PC Software

Comes with a graphical host software application featuring quick-access graphical buttons and extensive graphical manipulation capabilities. The software also provides clear numeric and waveform displays for real-time measurement data, and results can be exported and saved in Excel format for subsequent analysis with specialized software, making testing effortless. In addition, we offer full support for Python, MATLAB and LabVIEW application programming interfaces (APIs).

Signal channels
        Voltage input mode                Single-ended or differential input
        Full-scale sensitivity                1 nV to 5 V, stepping in 1-2-5 multiples
        Current input gain                106V/A
        Input impedance
                Voltage                      10 MΩ//10 pF, AC or DC coupling
                Current                      1 kΩ to virtual ground
        Common-mode rejection ratio                    >70 dB to 10 kHz, decreasing at 6 dB/oct
        Dynamic reserve                       >120 dB
        Gain accuracy                        Standard 0.5%, maximum 2%
        Voltage noise
                at 997 Hz              5 nV/√ Hz

Reference channel
        Input
                Frequency range               1 uHz to 100/500 kHz
                Reference input               Square wave or sine wave
                Input impedance               10 MΩ
                Square-wave reference level         VIH>3V， VIL<0.5V
                Sine reference signal         >2 Hz
                                             >400 mVpp
        Phase
                Resolution                   1udeg
                Absolute Phase Error         <1deg

                Relative phase error         <0.001deg

                Orthogonality
                        Internal reference         At 1 kHz: <0.0001°rms
                        External reference         At 1 kHz: 0.005°rms (time constant 100 ms, 12 dB/oct)
                Temperature drift
                        Below 10 kHz     <0.01°/℃
                        Above 10 kHz     <0.1°/℃

        Harmonic detection                           2F, 3F, …nF to 100/500 kHz (n<65,535)

        Acquisition Time

                Internal reference                  Instant acquisition

                External reference                (3 cycles + 5 ms) or 40 ms

Demodulator

        Stability

                Digital Output                 No zero drift for all settings

                Display                        No zero drift for all settings

                Analog output                 All dynamic reserve settings less than 5 ppm/℃

        Harmonic suppression                         -90 dB

        Time constant                         1 us to 3 ks, 6, 12, 18, 24, 30, 36, 42, 48 dB/oct steep roll-off

        Synchronous filter                      Effective steep roll-off below 1 kHz and greater than 18 dB/oct

Signal generator

        Frequency

                Range                         1 uHz to 100/500 kHz

                Accuracy                         2 ppm + 10 uHz

                Resolution                      1 uHz

        Distortion                                 -70 dBc 

        Sine Amplitude                           0.001Vrms to 5 Vrms (resolution 1 mVrms)

                Error                         Standard 0.5% (f<10 kHz), max 2%

                Temperature stability               100 ppm/℃

        Sine output                           Sine signal, output impedance 50 Ω

        TTL sync output                     5V TTL/CMOS level, output impedance 200Ω

Auxiliary inputs and outputs

        CH 1 and CH 2

                Features                          Outputs X, Y, R, θ and harmonics

                Amplitude                          ±10 V

                Drive current                   ±30mA max

        AUX Inputs

                Features                          2-channel input

                Amplitude                          ±10 V, 1 mV resolution

                Impedance                          1 MΩ

Communication interface

        UART                               XH2.54-4PIN

        Ethernet port                                  Isolated 1000Mbps RJ45 interface

Others

        Power requirements

                Voltage                          12VDC±5%

                Power                          18 W typical, 24 W maximum

        Dimensions

                长                              180 mm

                深                              106 mm

                高                               44 mm

Scanning microscope            AFM, STM, SPM

Materials science                Carrier mobility, carrier density, Hall effect, ultrasonic materials

Transport measurement                Conductance measurement, impedance measurement

Noise characterization                Noise density, cross-correlation measurement

Optical experiments                Spectral analysis, spectral measurement, THz measurement, TDLAS

Sensor measurement            Gyroscopes, photoelectric sensors, resonators, accelerometers

Magnetic Sensing                SQUIDs, NV centers, atomic magnetometers, VSM

Biomedical                Microfluidics