LeCroy Waverunner2 LT262 Series, Service Manual

Page: 28 / 155

4-10 Theory of Operation
4.2 Main Board
Introduction
The main board is divided into the following sections:
•
Front End
Based on the Hybrid HFE428, HSY632 switchyard to combine the input
channels.
•
A/D Converter & Digital Acquisition Memory
Based on the HAM631.
•
Trigger
Based on the Hybrids HTR420 discriminator & MST429A smart trigger.
•
Timebase
Based on the MCG426 clock generator & MTB411A controller
•
Main Board Control
4.2.1 Front End
The front end processes an analog signal for ADC and trigger, consists of High
impedance buffer, amplifier HFE428, and trigger comparator HTR420.
The main functions of the Front end without the amplifier HFE428 and HTR420 are:
•
Four channels opertion, calibration with Software control.
•
Input protection (clamp+thermal detection) and coupling (AC, DC, 1M
Ω
, 50
Ω
).
•
Attenuator by 10 & by 100.
•
Offset control.
•
Offset control of
±
1V and CAL control of
±
1.4V.
•
Detection of 50
Ω
over loading.
•
Input of signal for calibration.
The main functions of HFE428 are:
•
Amplitude normalization for the ADC system : at the BNC the dynamic range is 16
mV to 80V FS (full scale) and the ADC/TRIG system input is 500 mV differential.
•
Fine adjustment of gain and variable control
•
Band width limiter of 20MHz, 200MHz
Main function of HFE420 are:
•
Generation of trigger signal (analog input and digital output) with comparator
•
Setting of trigger level (TRIG,VALIDATE)
•
Setting of trigger coupling (DC,AC,LFREJ,HFREJ,HF)
•
Setting of slope (+,-,WINDOW)