Stanford Research SR850 – DSP Dual Phase Lock-In Amplifier

The Stanford Research SR850 is a high-performance DSP dual phase lock-in amplifier engineered for precision signal measurement in noisy environments. Using advanced digital signal processing, it replaces traditional analog components with precise mathematical calculations, delivering >100 dB dynamic reserve, 0.001° phase resolution, and 6 nV/√Hz input noise at 1 kHz. The instrument detects signals at any integer harmonic of the reference frequency up to 102.4 kHz, with differential or single-ended voltage inputs ranging from 2 nV to 1 V full scale, plus selectable current input gains of 10⁶ or 10⁸ V/A.

– Technical Specifications

• Frequency Range: 1 mHz to 102.4 kHz
• Dynamic Reserve: >100 dB
• Phase Resolution: 0.001°
• Voltage Input Noise: 6 nV/√Hz at 1 kHz
• Current Input Noise: 0.13 pA/√Hz at 1 kHz (10⁶ V/A); 0.013 pA/√Hz at 100 Hz (10⁸ V/A)
• Voltage Sensitivity: 2 nV to 1 V full scale
• Input Impedance: 10 MΩ + 25 pF (AC or DC coupled)
• Gain Accuracy: ±1% (±0.2% typical)
• CMRR: 100 dB at 10 kHz (decreases 6 dB/octave above 10 kHz)
• Line Filters: 50/60 Hz and 100/120 Hz (Q=5)
• Reference Oscillator Accuracy: 25 ppm + 30 µHz
• Internal Reference Distortion: <−80 dBc (f < 10 kHz); 10 kHz) at 1 Vrms
• Internal Reference Amplitude: 0.004 to 5 Vrms into 10 kΩ
• Phase Noise (Internal): <0.0001° rms at 1 kHz
• Phase Noise (External): 0.005° rms at 1 kHz, 100 ms, 12 dB/oct
• Phase Drift: <0.01°/°C below 10 kHz; <0.1°/°C from 10 kHz to 100 kHz
• Orthogonality: 90° ± 0.001°
• Time Constants: 10 µs to 30 ks
• Filter Rolloffs: 6, 12, 18, and 24 dB/octave

– Key Features

• Dual-phase detection with 0.001° phase resolution and <0.0001° rms internal phase noise
• Harmonic detection to 102.4 kHz with internal synthesized or external reference capability
• Synchronous filtering below 200 Hz for notch filtering of harmonic multiples
• High input impedance (10 MΩ) with 100 dB CMRR at 10 kHz
• Selectable line filters (50/60 Hz and 100/120 Hz) with Q=5

– Typical Applications

• Optical and photoacoustic spectroscopy
• Materials characterization and impedance analysis
• Low-frequency signal recovery in electronics and physics research
• Harmonic analysis and noise-immune measurements

– Compatibility & Integration

Accepts differential or single-ended voltage inputs, internal or external reference sources, and external sine or square wave references (minimum 400 mVpp). Reference outputs include sine and TTL signals with phase-lock capability to external references.