Hologic DISCOVERY A, Technical Manual

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Discovery QDR Series Technical Manual
2-27
2.13 Analog To Digital Board (A Model Only)
The Analog to Digital (ADC) board converts analog signals received from the Integrator/
Multiplexor board to a digital format. Analog signals from the Integrator/Multiplexor
board are applied to differential amplifiers on the ADC board in four groups of 64
channels. Outputs from the differential amplifiers are combined in a final multiplexor
consisting of four analog switches. The multiplexed signals pass through a programmable
gain amplifier and summing amplifier before being applied to an A/D converter. A one-
volt fixed DC offset is inserted at the summing amplifier to insure that no channels ever go
negative. The A/D converter converts the analog signal into 16-bit parallel data for
processing by a Digital Signal Processor.
The ADC board uses a Motorola 56000 Digital Signal processor to generate all the control
signals necessary for the detector array assembly. The same software can now be used
with all Discovery systems. This processor also provides a high-speed serial data link to
the computer.
Note: Jumper JP5, on the ADC board, is used to select between high- and low-resolution
so that the board can be used on both QDR-4500 and Discovery models. When the jumper
is in the board is configured for high-resolution, when the jumper is out the board is
configured for low-resolution. This jumper must always be present on Discovery A/SL
models.
2.13.1 Power
The ADC board re/-15V and + 7V from the C-arm Interface board. The +/-15V is
passed through this board to the Integrator/multiplexor board. It is also reduced to +/-12V
by series regulators to power op-amplifiers and analog switches located on this board. The
+/-15V also gen/-5V to power the analog-to-digital converter circuit. The +7V is
reduced to +5V to power the digital section of this board. The +5V is also passed on to the
Integrator/Multiplexor board.
2.13.2 Interface Connections
Figure 2-12 shows the interconnections between the Analog/Digital Converter board and
the Integrator/Multiplexor board. Table 2-16 describes the interface signals and identifies
the interconnection connector and pin assignments.