  The Teledyne HxRG detectors have versatile and programmable output options to
allow operation of them in a variety of configurations such as slow unbuffered,
slow buffered, fast buffered or unbuffered modes to optimise the detector
performance for a given application. Normally at ESO, for low noise operation,
the detectors are operated in slow unbuffered mode. Whilst the slow unbuffered
mode offers a simple interface to the external preamplifier electronics, the
detector operation in this mode can suffer from reduced pixel frequency
response and higher electrical crosstalk between the readout channels. In the
context of the detector systems required for the first generation instruments
of the ELT (MICADO, HARMONI and METIS), an exercise was undertaken to evaluate
the noise, speed and crosstalk performance of the detectors in the slow
buffered mode. A test preamplifier has been designed with options to operate a
H2RG detector in buffered or unbuffered and with or without using the reference
output, so a direct performance comparison can be made between different modes.
This paper presents the performance advantages such as increased pixel
frequency response, elimination of electrical crosstalk between the readout
channels and the noise performance in the buffered mode operation. These
improvements allow us to achieve the same frame readout time using half the
detector cryogenic electronics and detector controller electronics for the ELT
instruments, which significantly reduces the associated cryomechanical
complexities in the instrument.
