OE1201 Digital Lock-In Amplifiers

Overview
Now OE1201 DSP Lock-In Amplifier is the newest product of core technology with high performance. Based on the high-speed 4-core architecture, high-precision stabilized
ADC and excellent analog performance, it is ideal to detect the weak signals, which are overwhelmed by greatly larger noise components. And OE1201 could measure the
magnitude and phase of a signal simultaneously. It could be comparable with the international leading technology in some core parameters, like accuracy of measurement, range of operating frequency, SNR, dynamic reserve and so on.

Input Channel

With the excellent low-noise analog pre-amplifier, the signal input of OE1201 can be switched to operate in the single-ended or differential voltage mode, and the input noise is 10nV/√Hz. The input impedance is 10 M? and the full-scale input voltage sensitivity ranges from 1 nV to 1V. Besides,OE1201 can also be used for current measurements with6 8variable current gains of 10 or 10 V/A. 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 OE1201 has inherently large dynamic reserve up to 100dB.

Reference Channel

The reference signal for Oe1201 can be 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 sine wave output that multiplies the input signal,there is virtually no reference phase noise when choosing internal reference mode. Taking advantage of digital phase-
shifting technique, the reference signal phase could be adjusted with 0.01° resolution. The internal reference mode can operate at a fixed frequency from 50 mHz to 120 kHz. In addition, the external reference is also applicable to OE1201,including the sine wave reference signal and TTL logic
reference signal. The rising and trailing edge of external reference signal are applied to trigger off the internal Phase Locking Loop (PLL). Based on the frequency of reference signal, harmonic detection can be performed by OE1201. The maximum frequency of the measurable harmonics is 32767 times of basic frequency, and it is also less than the maximum operational frequency 120 kHz.

Digital Demodulator and Output Filter

The core of Lock-In Amplifier OE1201 is demodulator. This digital demodulator could be effectively immune from the potential errors caused by DC drift and offset found in analog multipliers or switches. The coherent signal multiplication has been optimized for very low calculation error. The time constants of OE1201 could be configured extending from 10 μs to 30 ks. The roll-offs of the output low-pass filter on OE1201 are 6, 12, 18 and 24 dB/octave. This low-pass filter is carried out by the architecture of digital infinite impulse response (IIR) filters and updated at 485 kHz signal sampling rate. The advantages of this design over common analog instruments are higher dynamic reserve (>100dB), accurate phase shifts (absolute phase error <1°), zero drift, and orthogonality. Meanwhile, below 20 Hz, OE1201 can perform synchronous filtering, which is used to notch out multiples of the reference frequency. This function ensures that OE1201 works quickly at low frequency.

Display

OE1201 uses the 3.5 inch 320×240 TFT color display as its screen. Data measured by OE1201, such as, X, Y, R, θ, is stored in up to four traces.

Internal Oscillator

The internal oscillator helps to generate a very low distortion (–80 dBc) reference signal. The single frequency of sine waves can be extended from 50 mHz to 120 kHz while the resolution generated is 0.1 mHz. Both frequency and amplitude can be set from the front panel or a computer. When choosing external reference mode, the internal oscillator is phase-locked to the external reference signal.

Signal Generator

OE1201 generates one sinusoidal signal in range from 50mHz to 120 kHz, using 16-bit low noise D/A converter. The frequency and phase shift of this sinusoidal signal are corresponding to that of the internal reference signal, and its amplitude could be set with control menu. The maximum amplitude provided by signal generator is 1Vrms.

Manual Operation

In addition to displaying data, the color TFT display panel is also used to display the control menu. In conjunction with keys grouped around the screen and numeric keypad,customers could adjust instrument's parameters effectively, such as oscillator frequency, which can be set to a fixed value and to a high precision.

Interface

OE1201regards 9-pin RS-232 and RS-232 to USB interfaces as standard. And, all instrument functions can be controlled and read through USB or RS-232 interfaces. To debug conveniently, all of the interfaces could be viewed on front panel. For convenient debugging, characters received and sent via interfaces can be viewed on front panel.

Remote Operation

The built-in RS232 to USB interfaces on OE1201 allow full manual operation from a controlling computer, including setting or interrogating control and reading out data. Free LabVIEW program is provided. It makes it easy to set up and run complex experiments, such as remote control of every
instrument function. The display menu offered by the LabVIEW program allows customers observe all command received and responses generated by instrument.