477 AC Current Pre-amplifier

The 477 is used as a pre-amplifier for a lock-in amplifier in AC systems employing current source detectors such as photomultipliers and photodiodes which, at low frequencies, give their best performance when connected to a virtual ground.

The virtual earth inputs (two) of the amplifier ensure that the detector is kept in short circuit condition, whereby no voltage is generated across the detector as a result of the photocurrent it produces. This short circuit operation enhances the linearity of detectors, reduces the effect of cable capacitance and is often a necessary condition in the determination of detector responsivity.

Used in conjunction with the 496 lock-in amplifier, the 477 allows the user to select a combination of current and voltage gain which optimises the trade-off of noise performance versus DC current sinking.

Gain range and input in use may be selected via the USB interface.

The 477 is a single-width module, housed within the 417/417T base unit.

Core Features

Inputs 2, remotely/manually selected
Gain ranges 103 - 108 V/A
Maximum input 10mA
Frequency response See table below
Input impedance Virtual ground
Gain accuracy +1%
Gain stability 200ppm/oC
Output stability 5ppm/oC to 500ppm/oC depending on sensitivity
Interface USB (via 417/417T base unit)
Linearity <0.025% departure from linearity from zero to full scale
V/A Bandwidth (-3Db)
103 >1MHz
104 1MHz
105 260kHz
106 30kHz
107 23kHz
108 4kHz