50 MHz Current Amplifier

The HF2TA Current Amplifier converts up to 2 input currents into voltage outputs over a wide frequency range up to 50 MHz. It is an active probe that can be conveniently placed close to the measurement setup, and it supports most applications where a current needs to be converted into a voltage. The dedicated design of the HF2TA ensures stability and smooth operation over its entire frequency range.

The HF2TA is an ideal fit to the HF2 instruments series thanks to its single connector providing both power supply and remote control; it can be controlled by the same user interface on all HF2 instruments.

HF2TA compatible instruments

• HF2LI Lock-in Amplifier
• HF2PLL Phase-Locked Loop

Transimpedance architecture

Providing 2 input and 2 output connectors, the HF2TA features a transimpedance architecture with a variable precision resistor as the gain parameter (R). The transimpedance architecture matches the current through the feedback resistor and keeps the input at virtual ground. The second amplification stage provides decoupling from the first stage and an additional gain (G). The resulting output voltage corresponds to U = R * G * I.

JFET input amplifier

The input of the HF2TA is constructed with JFET amplifiers which provide very low-noise over a wide frequency range. Additionally, the ultra-low input bias current of typically 2 pA allows for precise current measurements at small signal amplitudes.

Input offset adjust

To account for unbalanced circuitry inside the operation amplifiers and to cope with other external sources of voltage offset, the HF2TA provides a specific compensation feature with a very fine granularity. The user simply adjusts for a previously measured offset inside the graphical user interface of the HF2 Instrument.

Bias Input and Auxiliary Output

The Bias Input allows driving the signal shields with defined bias voltage. This can be used for instance to power a photo diode connected with one shielded cable for power and signal, avoiding ground loops. The Auxiliary Output provides a low-noise power source able to run an external sensor or detector. The maximum output power is 100 mW.

Current amplifier settings

Configurable settings include the transimpedance (R1, R2), the output voltage gain (G1, G2), the switch to control signal shield bias, the AC/DC coupling switch to suppress DC current offsets, the offset voltage compensation adjustment and the output bias voltage.