SPIRE Design Description - Research Services

Draft SPIRE Design Description Document
4.1.2.1 Detector control unit (DCU)
The DCU acts as the interface between the analogue signals from the detectors and the digital DPU. A
schematic drawing of the DCU together with the detector train components in the FPU and the interfaces
with the DPU and FCU is shown in Figure 4-8. There are three basic board types used in the DCU; the
Lock-in Amplifier (LIA) boards, the Bias Boards and the Data Acquisition and Interface (DAQ + I/F)
boards. They are all connected by the motherboard, which forms the back plane for the other boards.
Figure 4-8 - Schematic representation of the DCU including it's interfaces with the FPU, DPU and FCU.
Detector Bias Generators: As described in §4.4.4, the detectors are differentially biased with an AC
voltage, which is provided by the Bias Generator board. Due to the criticality of this component of the
detector read out electronics, there is both a prime and redundant board for the bias signals. The amplitude,
frequency and phase of the bias signals are all software commandable with the XC-4010-200 FPGA chip on
the DAQ + I/F board. This FPGA generates a series of 12-bit words, which correspond to the amplitude of
the bias signal. These words are loaded into Analog Devices AD7475A, 12-bit DAC chips that generate the
analog bias signal. These signal are then amplified to the required amplitude with Analog Devices OP-400
operational amplifiers. The characteristics of the bias signal are summarized in Table TBD.
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