Digital Lock-In Amplifiers SR850 — DSP lock-in amplifier with graphical display SR850 DSP Lock-In Amplifier The SR850 is a digital lock-in amplifier based on an innovative DSP (Digital Signal Processing) architecture. The SR850 boasts a number of significant performance advantages over traditional lock-in amplifiers—higher dynamic reserve, lower drift, lower distortion, and dramatically higher phase resolution. In addition, the CRT display and 65,536 point memory make it possible to display and process data in a variety of formats unavailable with conventional lock-ins. · 1 mHz to 102.4 kHz frequency range · >100 dB dynamic reserve · 0.001 degree phase resolution · Time constants from 10 µs to 30 ks (up to 24 dB/oct rolloff) Digital Precision · Auto-gain, -phase, -reserve and -offset At the input of the SR850 is a precision 18-bit A/D converter which digitizes the input signal at 256 kHz. The A/D converter, together with a high-speed DSP chip, replace the analog demodulator (mixer), low-pass filters and DC amplifiers found in conventional lock-ins. Instead of using analog components, the SR850 is implemented by a series of precise mathematical calculations which eliminate the drift, offset, non-linearity and aging inherent in analog components. The same DSP chip digitally synthesizes the reference oscillator, providing a source with less than –80 dBc distortion, 100 mHz frequency resolution, and 2 mV of amplitude resolution. · Data logging (up to 65k samples) · Smoothing, curve fitting & statistics · GPIB & RS-232 interfaces Digital Flexibility The SR850 has a 7" CRT display which supports a large selection of display options. Data can be viewed numerically or graphically in bar graph, polar plot and strip chart formats. With 65,536 points of memory and data acquisition rates up Stanford Research Systems

to 512 Hz, you are able to see exactly how your data changes in time—not just what the current output value is. After the data has been acquired, the SR850 offers a variety of data reduction options, such as Savitsky-Golay smoothing, curvefitting and statistical analysis. A built-in 3.5” disk drive, along with standard RS-232 and GPIB interfaces, makes it easy to transfer data to your computer. Because the SR850 uses a digital phase-shifting technique rather than analog phase-shifters, the reference phase can be adjusted with one millidegree resolution. In addition, the X and Y outputs are orthogonal...

defining an appropriate trace. Trace values can be displayed as a bar graph with an associated large numerical display, or as a strip chart showing the trace values as a function of time. Additionally, you can display polar plots showing the phasor formed by the in-phase and quadrature components of the the SR850’s frequency scans. Both the A/D inputs and the D/A outputs have a ±10 V range. Analysis Features The SR850’s performance doesn’t stop once data has been acquired—a full set of data processing features is also included. Multiple-range Savitsky-Golay smoothing can be applied to any of...

Signal Channel Voltage inputs Single-ended or differential Sensitivity 2 nV to 1 V Current input 106 or 108 V/A Input impedance Voltage input 10 MΩ + 25 pF, AC or DC coupled Current input 1 kΩ to virtual ground Gain accuracy ±1 % (±0.2 % typ.) Noise (typ.) 6 nV/√Hz at 1 kHz 0.13 pA/√Hz at 1 kHz (106 V/A) 0.013 pA/√Hz at 100 Hz (108 V/A) Line filters 50/60 Hz and 100/120 Hz (Q = 5) CMRR 100 dB at 10 kHz, decreasing by 6 dB/oct above 10 kHz Dynamic reserve >100 dB (without prefilters) Interfaces X, Y outputs CH1 output CH2 output Aux. A/D inputs Aux. D/A outputs Sine out TTL out Trigger In Remote...