Manual

SECTION 3

THEORY OF OPERATION

GENERAL

Module Interface

Figure 3-1 shows a simplified block diagram of the Module Interface board. The path for communication

between mainframe and module is via PS. The eight QAD lines and five QA lines are the bus interface

lines, and a MOD DIS line is used for disabling the Output board. Power is also delivered by P8.

The address demultiplexer and select logic circuitry decodes the bus signals and selects one of the other

blocks.

The I.D. ROM contains information necessary for operation specific to the Output board. This includes

boundaries for parameters, values used to initialize the nonvolatile RAM (NVRAM), and the version

number of the I.D. ROM.

The nonvolatile RAM is used for saving and retrieving ten panel settings. It also holds the GPIB/RS232

bus settings.

The digital control circuits are used to monitor and set the operating state of the Output board. The DACs

and amplifiers allow setting of up to four analog values used for level control. All of the control, status,

and analog signals are delivered to the Output board by two 20-pin connectors, J1 and J2.

Laser Driver Output

Figure 3-2 shows a simplified block diagram of the Laser Output board. The connection to the Module

Interface board is shown in the lower left hand corner. There are three analog lines used to set the output

levels and the threshold of the External Drive discriminator. The control lines select which Mode the

Laser Output will operate in.

The selection of the digital drive source is controlled by three digital control lines, EXT DRIVE ENABLE,

IMPULSE, and EXT MOD. These determine which of the two drive sources will be controlling the state of

S1, (a high speed transistor switch). A discriminator, whose threshold is set by the analog voltage EXT

DRIVE LEVEL, is connected to the drive source from the front panel EXT DR connector. The other signal

source is the rear panel DRIVE connector which delivers the mainframe's pulse generator output.

The level control circuitry sets one or both of the current sources as determined by the analog inputs

PEAK LEVEL, and BASELINE LEVEL and the Mode control lines. During the Impulse, CY and External

Modulation Modes, it uses the PIN detector in the laser module to monitor and stabilize the laser's

output. When LASER GUARD is active, the current sources are set for zero output.