Programmable Filters SR640, SR645, and SR650 — High-pass and low-pass elliptical filters (2-channel) SR600 Series Programmable Filters · Two independent filter channels · 115 dB/octave rolloff · 1 Hz to 100 kHz frequency range · 0.1 dB passband ripple · 80 dB stopband attenuation · 6 nV/√Hz input noise The SR600 series consists of three dual-channel instruments. Each instrument channel has a low-noise preamplifier, a precision high-pass or low-pass filter section, and an output amplifier. The filters are 8-pole, 6-zero elliptic-type with 115 dB per octave rolloff, 0.1 dB of passband ripple, and 80 dB stopband attenuation. Cutoff frequencies can be set between 1 Hz and 100 kHz, making the SR600 series ideal for applications including anti-aliasing, audio analysis, and general frequency-domain signal conditioning. Model — Configuration SR640 — dual low-pass SR645 — dual high-pass SR650 — high-pass/low-pass (can be cascaded for band-pass) Stanford Research Systems Each filter channel has a floating, differential input with 1 MΩ input impedance and 6 nV/√Hz of input noise. The analog ground for each filter channel is available at a rear-panel BNC connector to provide complete flexibility in grounding. The filter grounds may be tied to the instrument’s chassis ground or to any other point. Both AC and DC input coupling can be selected, and an invert key allows the phase of the signal to be shifted by 180° with a single key press. Up to 60 dB of preamplifier gain can be specified in 10 dB increments. A simple offset adjust screw lets you null DC components in your signal.

SR600 Series Programmable Filters Filter Characteristics Filter characteristics for the SR600 series are shown below. The exact filter transfer function is given in the specifications section. (The graph shows the low pass response. The highpass response is found by inverting the curve around f = 1.) The large amount of excess phase, typical of elliptical filters, makes the SR600 series filters optimum in frequencydomain applications. Note that the 0.1 dB passband ripple specification for the SR640 series filters is a measured specification, not just the theoretical passband ripple of the transfer...

Frequency range 1 Hz to 100 kHz (3-digit resolution) Type 8-pole, 6-zero elliptic Rolloff 115 dB/octave Passband ripple 0.1 dB peak to peak (typ.) Stopband attenuation 80 dB (typ.) Impedance <1 Ω Full-scale output signal 10 Vpp into >300 Ω Option 01 10 Vpp into 50 Ω DC offset Adjustable to 0 V Gain 0, 10, 20 dB ± 0.5 dB Harmonic distortion <–80 dB below full scale at 100 Hz (<1 Vpp output) <–50 dB below full scale at 1 kHz Spurious components <–80 dB below full scale (with input source <50 Ω) Channel crosstalk <–110 dB below full scale (with input source <50 Ω) Phase match ±0.75° (DC to fc, typ.)...