LeCroy LC564DL, Service Manual

Page: 34 / 210

4-10 Theory of Operation
4.2 900079 Main Board
4.2.1 Introduction
The board is divided into five sections :
•
Microprocessor control based on the MTC428 EPLD pair.
•
Front-end based on the Hybrid HFE444 & HSY430 switchyard board to combine
the input channel.
•
Trigger based on the Hybrids HTR420 discriminator & MST429A smart trigger
•
Analog Converter based on the HAM435 Sample&Hold and A/D converter
and MNX427 min/max to pre-compute the data.
•
Digital Acquisition based on the HMM434 Acquisition memory and SIMM DRAM
module for buffer memory.
•
Time base based on the MCG426 clock generator & MTB411A controller
4.2.2 Front End
The front-end system provides the signal conditioning for the ADC system.
All channel are identical, thus only one channel will be described here.
The main functions of the Front end without the amplifier (HFE444) are:
•
Four channels operation, calibration with Software control
•
Input protection (clamp + thermal detection) and coupling (AC, DC, 1 M
Ω
, 50
Ω
).
•
Attenuator by 10 in the 50
Ω
path and attenuator by 20 in 1M
Ω
path.
•
Offset control and CAL control.
The main functions of HFE444 are:
•
Amplitude normalization for the ADC system : at the BNC the dynamic range is
16 mV to 8V FS at 50
Ω
and to 16V FS (full scale) at 1 MOhm in a 1-2-5 step
sequence and the ADC system input is 500 mV differential.
•
Fine gain control to fill in the fixed vertical sensitivities.
•
Bandwidth limit filter at 25 MHz and 200 MHz.