Digital Lock-In Amplifiers SR810 and SR830 — DSP lock-in amplifiers SR810 & SR830 DSP Lock-In Amplifiers The SR810 and SR830 DSP Lock-In Amplifiers provide high performance at a reasonable cost. The SR830 simultaneously displays the magnitude and phase of a signal, while the SR810 displays the magnitude only. Both instruments use digital signal processing (DSP) to replace the demodulators, output filters, and amplifiers found in conventional lock-ins. The SR810 and SR830 provide uncompromised performance with an operating range of 1 mHz to 102 kHz and 100 dB of driftfree dynamic reserve. · 1 mHz to 102.4 kHz frequency range · >100 dB dynamic reserve · 5 ppm/°C stability · 0.01 degree phase resolution · Time constants from 10 µs to 30 ks (up to 24 dB/oct rolloff) Input Channel The SR810 and SR830 have differential inputs with 6 nV/√Hz input noise. The input impedance is 10 MΩ, and minimum full-scale input voltage sensitivity is 2 nV. The inputs can also be configured for current measurements with selectable current gains of 106 and 108 V/A. A line filter (50 Hz or 60 Hz) and a 2× line filter (100 Hz or 120 Hz) are provided to eliminate line related interference. However, unlike conventional lock-in amplifiers, no tracking band-pass filter is needed at the input. This filter is used by conventional lockins to increase dynamic reserve. Unfortunately, band pass filters also introduce noise, amplitude and phase error, and drift. The DSP design of these lock-ins has such inherently large dynamic reserve that no band pass filter is needed. · Auto-gain, -phase, -reserve and -offset · Synthesized reference source · GPIB and RS-232 interfaces Extended Dynamic Reserve Stanford Research Systems The dynamic reserve of a lock-in amplifier, at a given fullscale input voltage, is the ratio (in dB) of the largest interfering

signal to the full-scale input voltage. The largest interfering signal is defined as the amplitude of the largest signal at any frequency that can be applied to the input before the lock-in cannot measure a signal with its specified accuracy. signal is quickly nulled with the auto-offset function, and resolution is increased by expanding around the relative value by up to 100×. Harmonic detection isn’t limited to 2F — any harmonic (2F, 3F, ... nF) up to 102 kHz can be measured. Conventional lock-in amplifiers use an analog demodulator to mix an input signal with a reference signal. Dynamic reserve...

Signal Channel Voltage inputs Single-ended or differential Sensitivity 2 nV to 1 V Current input 106 or 108 V/A Input impedance Voltage 10 MΩ + 25 pF, AC or DC coupled Current 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 = 4 ) CMRR 100 dB to 10 kHz, decreasing by 6 dB/oct above 10 kHz Dynamic reserve >100 dB (without prefilters) Stability <5 ppm/°C Displays Channel 1 Channel 2 (SR830) Offset Expand Reference Reference Channel Frequency range 0.001 Hz...