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. Conventional lock-in amplifiers use an analog demodulator to mix an input signal with a reference signal. Dynamic reserve is limited to about 60 dB, and these instruments suffer from poor stability, output drift, and excessive gain and phase error. Demodulation in the SR810 and SR830 is accomplished by sampling the input signal with a high-precision A/D...

Signal Channel Voltage inputs Sensitivity Current input Input impedance Voltage Current Gain accuracy Noise (typ.) Line filters CMRR Dynamic reserve Stability Reference Channel Frequency range Reference input Input impedance Phase resolution Absolute phase error Relative phase error Orthogonality Phase noise Internal ref. External ref. Phase drift Harmonic detection Acquisition time Single-ended or differential 2 nV to 1 V 106 or 108 V/A 10 MQ+25 pF, AC or DC coupled 1 kQ to virtual ground ±1 % (±0.2 % typ.) 6 nV/yHz at 1 kHz 0.13 pA/VHz at 1 kHz (106 V/A) 0.013 pA/VHz at 100 Hz (108 V/A) 50/60...