The Stanford Research Systems SR650 is a dual-channel programmable filter for precision signal processing across 1 Hz to 100 kHz. It combines an 8-pole elliptic filter with 115 dB/octave rolloff and low-noise preamplifiers (6 nV/√Hz) to deliver exceptional stopband attenuation (80 dB typical) and passband ripple control (0.1 dB peak-to-peak). High-pass, low-pass, and cascaded band-pass configurations isolate signals while optimizing signal-to-noise ratio. The instrument supports selectable AC/DC input coupling, up to 60 dB preamplifier gain, and 10 Vpp output into >300 Ω (or 50 Ω with Option 01). All settings—including cutoff frequencies, amplifier gains, and complete instrument configurations—are programmable via GPIB or RS-232 interfaces. The SR650 stores up to nine configurations in non-volatile memory and adjusts cutoff frequencies in under 100 ms. A low-power microprocessor design reduces digital noise during idle periods. Phase match between channels reaches ±0.25° below 10 kHz and ±0.75° across the full range.
Technical Specifications
• Filter Architecture: 8-pole, 6-zero elliptic-type with 115 dB/octave rolloff
• Frequency Range: 1 Hz to 100 kHz (3-digit resolution)
• Passband Ripple: 0.1 dB peak-to-peak (typical)
• Stopband Attenuation: 80 dB (typical)
• Input Impedance: 1 MΩ differential (floating)
• Input Noise: 6 nV/√Hz
• Preamplifier Gain: 0–60 dB (10 dB increments)
• Output Levels: 10 Vpp into >300 Ω (Option 01: 10 Vpp into 50 Ω)
• Output Gain: 0, 10, 20 dB ± 0.5 dB
• Harmonic Distortion: <–80 dB below full scale at 100 Hz (<1 Vpp); <–50 dB at 1 kHz
• Spurious Components: <–80 dB below full scale (source <50 Ω)
• Channel Crosstalk: <–110 dB below full scale (source <50 Ω)
• Phase Match: ±0.25° (below 10 kHz); ±0.75° (DC to fc, typical); <±0.75° (worst case, DC to 100 kHz)
• Frequency Adjustment Time: <100 ms
– Key Features
• Two independent filter channels with AC/DC input coupling selection
• Floating differential input with rear-panel analog ground reference flexibility
• Adjustable DC offset null and 180° phase invert
• Nine non-volatile memory slots for complete instrument configurations
• Cutoff frequency setting from 1 Hz to 100 kHz
• Low-power CMOS microprocessor with sleep mode for noise reduction
• Programmable via GPIB or RS-232 interfaces
– Typical Applications
• Anti-aliasing filtering for data acquisition
• Audio frequency analysis and conditioning
• Research-grade signal isolation and frequency-domain processing
• Industrial signal conditioning
– Compatibility & Integration
• Standard interfaces: GPIB, RS-232
• Power: 100, 120, 220, or 240 VAC nominal (50 or 60 Hz)
• Front-panel and computer-controlled configuration management
