Hologic DISCOVERY A, Technical Manual

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Discovery QDR Series Technical Manual
2-23
2.11 Data Acquisition System (A Model only)
The Discovery A Data Acquisition System (DAS) consists of three Solid State Detector
printed circuit boards, an Integrator/Multiplexor board, and an Analog to Digital
Converter (ADC) board. The Solid State Detector boards and the Integrator/Multiplexor
board are physically located within the upper end of the C-arm. The detector boards mount
under the Integrator/Multiplexor board and connect to the Integrator/Multiplexor board.
The Integrator/Multiplexor board is contained in an electrically shielded enclosure. There
is also a lead radiation shield between the detector and the integrator/multiplexor boards to
stop any X-rays that might get through the detectors. The ADC board is located within the
rear downward slope of the C-arm.
2.11.1 Solid State Detector
The Solid State Detector boards convert X-rays into signals that are applied to the
Integrator/Multiplexor board. X-rays striking detector crystals are converted into visible
light. Solid State photodiodes sense this light and convert the light into current, which is
amplified in a current to voltage converter. Output from the amplifier is applied to the
Integrator through analog switches. The analog switches all operate in parallel and are
turned on during the X-ray pulse. These switches are turned off during the integrator hold
time to prevent integrating noise into the data. The turning on and off of these switches is
controlled by the INTEGRATE signal supplied from the Integrator/Multiplexor board.
Each solid-state detector board has a capacity of 72 high-resolution detectors. This is
equal to slightly less than 1mm resolution in an AP spine. The detector array contains 216
2mm detectors.
2.11.2 Power
The Solid State Detector board re/-15V from the Integrator/Multiplexor board.
Voltage regulators, located on this board, convert this voltage to +/-12V to power the
amplifiers and switches.
2.11.3 Interface Connections
Figure 2-10 shows the interconnections between the Integrator/Multiplexor board and the
Solid State Detector boards. Table 2-14 describes the interface signals and identifies the
interconnection connector and pin assignments.
INTEGRATOR/MULTIPLEXOR
BOARD
CHANNEL0 - CHANNEL215
INTEGA - INTEGF
+15V
15V_RET
-15V
SILICON
DETECTOR
BOARDS