4.2.1 Front End
The front end processes an analog signal for ADC and trigger, consists of 1M ohms
attenuators, high impedance buffer, 200 ohms attenuator, variable gain amplifier
SA5209D and differential amplifiers.
The main functions of the Front end without the amplifiers are:
• Four channels operation, calibration with Software control.
• Input protection (clamp + thermal detection) and coupling (AC, DC, 1MΩ, 50Ω).
• Attenuator by 5, by 10, by 50, by 100 & by 500.
• Offset control of ±1V.
• Detection of 50Ω over loading.
• Input of signal for DC calibration and skew calibration.
The main functions of SA5209D and differential amplifiers 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.
• Switch for channel combine mode.
Control
Relay control
The relay of the attenuator is set by selecting the input coupling and the gain as shown in
the table below.
All relays are driven with +5V/0V.
Input coupling
Control port Relay GND 1M,DC 1M,AC 50,DC
CAL RL2 H L L L
1M/*50 RL1 H H H L
AC/*DC RL5 H L H L
1/*10 RL3 H X X X
1/*100 RL4 L X X X
Switch of attenuator
Control port Relay 2mV-49mV 50mV-0.49V 0.5V-10V
1/*10 RL3 H L L
1/*100 RL4 H H L
Theory of Operation 4-3
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