Introduction

Presently, the McDonald Observatory only operates one modern near-IR (0.9p,m <A< 2.5p,m) instrument, LRS-J, and thus this paper focuses strongly on the specifics of that instrument and its HAWAII-1RG detector. In practice, we can operate any nRG device without modification and many other near-IR detectors by only implementing new gain settings within the preamplifier stages.

The LRS-J detector controller is based on the McDonald Observatory V2 CCD controller, with minor modifications to two modules: the Penthouse/preamplifier (PH) module, and the Clock Driver (CD) module (see Fig. 1).

The V2 controller is a true 18-bit 2/4 channel 100 kpix/s system. Although the 1RG doesn't require an 18-bit system, because of its limited dynamic range, these modules exist and operate fast enough to acquire 16-bit data by simply not using the 2 LSBs. System noise in this configuration is essentially non-existent.

Figure 1. (left) McDonald Observatory V2 controller. (middle and right) The HAWAII-nRG specific clock driver and Penthouse modules.

With few exceptions, the required modifications were made simply to decrease risk to the array. For example, in the CD module, the Thaler VRE310 was replaced with a 3.000 V VRE303J to limit the allowable voltage swing of the nRG clock inputs to a range of 0-3.3 V, all settable with 12-bit ADCs. In the PH module a similar philosophy (VRE402J) was employed. Gain in the preamp went up to ~28.0 V from the 8-20 V we use for CCDs. The PH module now outputs 0-10 V depending upon the 1RG detector signal.

The most esoteric change required bypassing (by occasionally lifting an SMD foot and soldering another component between the foot and its pad) the unused negative clock supplies required for CCD operation. Aside from the vacuum circuitry, no new Printed Circuit Boards (PCBs) were required to accommodate the new detector.

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