Trigger - LeCroy WaveSurfer 400 Series Service Manual

4 channels mode
CH1a SIG
CH1
Front
End
CH1b SIG
CH2b SIG
CH2
Front
End
CH2a SIG
CH3a SIG
CH3
Front
End
CH3b SIG
CH4b SIG
CH4
Front
End
CH4a SIG

4.2.3 Trigger

HTR420
The 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)
The different trigger couplings using HTR420 are :
• DC
• AC
• LF REJ
• HF REJ
• HF
TV Trigger
4-6 Theory of Operation
2
20RL1 CH1 ADC
Differencial
2
CH1 signal
20RL2 CH2 ADC
CH2 signal
21RL1 CH3 ADC
CH3 signal
21RL2 CH4 ADC
CH4 signal
Figure 4-6 4 & 2 Channel Mode
: cut off frequency is almost 7.5 Hz.
: single pole high pass filter with a cut off frequency at 50 kHz.
: single pole low pass filter with a cut off frequency at 50 kHz.
: frequency divider by four for high frequency signal.
Each channel has a pick-off after the HTR420. Selected trigger source goes to
commercial chip (LM1881) via AGC amplifier and provides three outputs
(Composite Sync. Output, Vertical Sync. Output, and ODD/EVEN output) to the
MST429A.
Channel combine mode
(CH1 & CH3)
CH1a SIG
CH1
Front
HAM631
End
CH1b SIG
CH2b SIG
HAM631 CH2
Front
End
CH2a SIG
CH3a SIG
CH3
Front
HAM631
End
CH3b SIG
CH4b SIG
HAM631 CH4
Front
End
CH4a SIG
2
20RL1 CH1 ADC
Differencial
2 HAM631
CH1 signal
20RL2 CH2 ADC
HAM631
CH1 signal
21RL1 CH3 ADC
HAM631
CH3 signal
21RL2 CH4 ADC
HAM631
CH3 signal