With the low-noise analog pre-amplifier, the signal input of OE2042 can be switched to operate in the single-ended or differential voltage mode, and the input noise is 10nV/√Hz@100kHz. The input impedance is 50Ω 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 OE2042 has 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 OE2042, an external sine or TTL signal, 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 digital phaseshifting technique, the reference signal phase could be adjusted with 0.01° 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 OE2042, including the sinewave reference signal and TTL logic reference signal. The rising and falling 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 OE2042. The maximum frequency of the measurable harmonics is 32767 times of basic frequency, and it is limited to the maximum operational frequency 60MHz.
The core of Lock-In Amplifier OE2042 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 OE2042 could be configured extending from 30ns to 4.4ks. The roll-offs of the output low-pass filter on OE2042 are 6, 12, 18, 24, 30 ,36,42 and 48 dB/octave. This low-pass filter is carried out by the architecture of digital infinite impulse response (IIR) filters and updated at 250MHz signal sampling rate. The advantages of this design over
common analog instruments are higher dynamic reserve (>120dB), accurate phase shifts (absolute phase error <1°), zero drift, and orthogonality. Meanwhile, below 200 Hz, OE2042 can perform synchronous filtering, which is used to notch out multiples of the reference frequency. This function ensures that OE2042 works quickly at low frequency.
The internal oscillator helps to generate a very low distortion (–80 dBc) reference signal. The single frequency of sine waves can be extended from 1 mHz to 60MHz while the resolution generated is 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.
OE2042 generates one sinusoidal signal in range from 1mHz to 60MHz, using 14-bit 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 with 1uVrms accuracy.
OE2042 uses the 5.6 inch 640×480 TFT color display as its screen. Data measured by OE2042, such as, X, Y, R, θ, is stored in up to four traces. Trace values can be displayed as a bar graph or as a strip chart showing the trace values as a function of time.
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.
OE2042 has the ability to adjust measurement parameters to optimum setting for input signal. Gain, phase, dynamic reserve and display scaling could all be set with different independent key presses from the control menu. With this function, the input signals could be measured easily and automatically.
The built-in RS232、 USB 2.0 and enthernet interfaces on OE2042 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 and save the data. The display menu offered by the LabVIEW program allows customers observe all command received and responses generated by instrument.