SPIRE Design Description - Research Services

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Draft SPIRE Design Description Document The DRCU comprises 4 physical sub-units: (i) the DCU which includes the detector control, biasing, readout and digitization electronics; (ii) the MCU includes the mechanisms’ (FTS+BSM) control electronics; (iii) the SCU includes the sub-system control electronics; and (iv) the PSU which takes power from the spacecraft power bus and converts it to the required voltage for the other sub-units of the DRCU. These components are schematically represented in Figure 4-7. Figure 4-7 - Schematic block diagram of the DRCU including the interfaces to the DPU and the FPU. 62
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. 63
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