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Low Noise | High Stability I to V Converter


The low-noise high-stability (LNHS) I to V Converter offers ultra-low noise, excellent stability, and unique features such as a floating input and the possibility to apply an external bias voltage. We carefully screen and select only the best, lowest noise transistors for the input stage.

The units are small and light and can easily be mounted close to the experiment, e.g., directly on the breakout box or the cryostat. The I to V converter offers five decades of gain, from 10^5 to 10^9 V/A, and an integrated low-pass filter with a cut-off between 30 Hz and 100 kHz. A remote control unit is available to adjust gain and filter settings remotely. The bandwidth varies from 1.7 kHz at maximum gain (10^9 V/A) to 600 kHz at minimum gain (10^5 V/A).

One may supply an external bias voltage of ±100 mV (model SP983c), ±1 V (model SP983c01) or ±2 V (model SP983c02) on the I to V converter input, making it possible to measure current at an arbitrary bias voltage or do symmetric source-drain voltage biasing. The externally applied input bias voltage is internally subtracted and does not go on top of the output signal.

While all preamplifiers put out a small voltage bias at their inputs, our I to V converter is the only preamplifier that stabilizes this input voltage bias with an active feedback loop to below 0.2 μV/K. In experiments where the voltage applied to the device is relevant to the μV level, the stabilized input voltage bias is very valuable. In other commercial instruments, the input voltages may drift by many 10s of μVs over time. 

Our devices are designed for low-temperature (dilution fridge) experiments. The IF3602 input stage (see the input stage options below) is optimized for large load capacitances such as those from heavily filtered leads in low-temperature experiments. 

The I to V converter's output ground is isolated from the power supply and the computer interface. Hence, the cables coming from the experiment provide the measurement ground. This grounding scheme helps avoid ground loops without a need for batteries and enables an ultra-low noise setup. 

We offer two different J-FET options for the input stage of the I to V converter:

LSK389A: best for R > 1 MΩ and C < 1 nF

Lower input current noise (significant in the 10^8 and 10^9 V/A ranges)

IF3602: best for R < 1 MΩ or C > 1 nF 

Slightly lower input voltage noise. Lager gain-bandwidth-product (600 MHz) makes output noise significant smaller at large input-capacitances.

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