Analog Lock-In Amplifiers SR124 — Analog lock-in amplifier SR124 Analog Lock-In Amplifier For over a half century, the lock-in amplifier has been the instrument of choice for measuring small AC signals in the presence of noise. Early instruments were designed with analog electronics, multi-gang mechanical switches, needle indicators, etc., and measurements were often monitored with chart recorders. Microprocessor based designs emerged in the 1980s, and by the early 1990s even the lock-in’s analog demodulators were replaced by high-resolution ADCs and digital signal processors (DSP). Remote computer control, digital readouts and user-friendly front panels all resulted. · Low-noise, all analog design · No digital interference · 0.2 Hz to 200 kHz measurement range · Low-noise current and voltage inputs · Harmonic detection (f, 2f, or 3f) The capabilities of the modern DSP lock-in amplifier in stability, dynamic reserve, and flexibility were revolutionary, making it a mainstay for researchers and engineers across multiple fields. But in moving forward, something was left behind. For a core group of users, including low-temperature researchers in particular, the new instruments became a potential source of high-frequency interference. This is best reflected in the persistence of one instrument — the PAR124A — still actively used by many researchers decades after discontinuation by its long-gone manufacturer. · Selectable input filtering Recognizing that one size shouldn’t have to fit all, SRS is proud to introduce the SR124 Analog Lock-In Amplifier. Inspired by the best of an earlier generation’s lock-ins, but availing itself of today’s low-noise analog components and design methodologies, the SR124 is an uncompromising tour de force in low-noise, high-performance analog instrumentation. Stanford Research Systems

SR124 Analog Lock-In Amplifier Architecture The SR124 design follows two basic themes. First, the signal path is entirely built from low-noise analog electronics: the best JFETs, transistors, op-amps, and discrete components. Second, configuration control is managed by a microcontroller whose system clock only oscillates during the brief moments needed to change gains or filter settings. This “clock-stopping” architecture, first introduced by SRS in the SR560 Voltage Preamplifier, eliminates the inconvenience and reliability issues associated with mechanical panel controls, and makes full remote...

SR124 Analog Lock-In Amplifier first chosen in the reference section of the front panel — either manually or by the auto Ref Range feature. be measured at a range of different bias values. Bias values can be set up to ±1000× the reference amplitude, depending on amplitude. In external reference mode, the SR124 will lock to external signals with at least 100 mVpp amplitude. The reference oscillator will phase-lock to the positive zero-crossings of the external reference input. Locking at f, 2f (second harmonic), or 3f (3rd harmonic) is supported. Phase Control The SR124 is a single phase lock-in...

Frequency accuracy 0.1 % Frequency resolution 3½ digits or 1 mHz, whichever is greater Amplitude 1 µV to 20 Vpp into 10 kΩ, 50 Ω output impedance. Amplitude stability 50 ppm/°C Signal Channel Voltage inputs Single-ended or differential Sensitivity 100 nV to 500 mV Current input 106 or 108 V/A Input impedance Voltage 10 MΩ + 35 pF, AC or DC coupled Current 1 kΩ to virtual ground Gain accuracy ±1 % Gain stability 100 ppm/°C (flat mode, normal reserve) Noise (rms) 2.5 nV/√Hz at 1 kHz 0.14 pA/√Hz at 1 kHz (106 V/A) 0.014 pA/√Hz at 100 Hz (108 V/A) Signal filters (Tunable from 0.2 Hz to 200 kHz) Flat...