High Frequency Lock-In Amplifier SR844 — 200 MHz dual phase lock-in amplifier SR844 200 MHz Lock-In Amplifier · 25 kHz to 200 MHz frequency range · 80 dB dynamic reserve · Time constants from 100 µs to 30 ks (6, 12, 18 or 24 dB/oct rolloff) · “No Time Constant” mode (10 µs to 20 µs update rate) · Auto-gain, -phase, -reserve and -offset · Two 16-bit DACs and ADCs The SR844 is the widest bandwidth lock-in amplifier available. It provides uncompromised performance with a frequency range of 25 kHz to 200 MHz and up to 80 dB of drift-free dynamic reserve. It includes the many features, ease of operation, and programmability that you’ve come to expect from SRS DSP ock-in amplifiers. l Digital Technology The SR844 uses the same advanced DSP technology found in the SR850, SR830 and SR810 lock-in mplifiers. DSP a offers many advantages over analog instruments — high dynamic reserve, low zero-drift, accurate RF phase shifts and orthogonality, and digital output filtering. Signal Input · Internal or external reference The SR844 has both 50 Ω and 1 MΩ inputs. The 1 MΩ input is used with high source impedances at low requencies, or f with a standard 10× scope probe. The 50 Ω input rovides the p best RF signal matching. Up to 60 dB of RF attenuation or 20 dB of RF gain can be selected in 20 dB increments. Full-scale sensitivities range from 1 Vrms (+13 dBm) to 100 nVrms (–127 dBm). Gain allocation can be optimized to provide up to 80 dB of dynamic reserve. Stanford Research Systems The SR844 offers both external and internal reference operation. In both cases, the entire 25 kHz to 200 MHz

frequency range is covered without any manual range selection. The external reference input has an auto-threshold feature which locks to sine, square or pulsed signals. The internal reference is igitally synthesized and is adjustable d with 3-digit frequency resolution. Transfer function measurements can be easily made from the front panel by a programmable scan of up to 11 frequencies. Setups and ffsets are recalled at each frequency in the scan. o Harmonic detection of the 2F component is available for both internal and external reference modes. The two displays each have a ser-defined output...

Signal Channel Voltage input Single-ended BNC Input impedance 50 Ω or 1 MΩ + 30 pF Damage threshold ±5 V (DC + AC) Bandwidth 25 kHz to 200 MHz Sensitivity <1 MHz 100 nVrms to 1 Vrms full scale <50 MHz 1 µVrms to 1 Vrms full scale <200 MHz 10 µVrms to 1 Vrms full scale Gain accuracy <50 MHz ±0.25 dB <200 MHz ±0.50 dB Gain stability 0.2 %/ºC Coherent pickup Low-noise reserve, sens. <30 mV f < 10 MHz <100 nV (typ.) f < 50 MHz <2.5 µV (typ.) f < 200 MHz <25 µV (typ.) Input noise (50 Ω) 2 nV/√Hz (typ.), <8 nV/√Hz (max.) Input noise (1 MΩ) 5 nV/√Hz (typ.), <8 nV/√Hz (max.) Dynamic reserve up to 80...