Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

I need help understand analog input stage of this DSO

Status
Not open for further replies.
analog input stage

It is needed because the input stage need a very high value input impedance in parallel with the 1Megohm so that the 1Meg resistive value for the input of the scope will be maintained and also very low bias current. Active probes use a similar FET buffer. If you remove it the input resistance and capacitance of the IC opamp will be in parallel with the input resistor.
 

    C

    cmos babe

    Points: 2
    Helpful Answer Positive Rating
input stage dso

Thanks so much for the answer! I have more question. What's the function of C31//R25 ? Aren't diodes enough for protection?
 

cmos babe said:
freepoint said:
no enough for protect.
Click to expand...

How?
Click to expand...
In case of high input voltage, the 10k resistor limits the current through the diodes. The 100pF capacitor bypasses the 10k at high frequencies to eliminate the frequency response rolloff that would otherwise be caused by the 10k and the capacitances of the diodes and the JFET gate capacitance.
 

    C

    cmos babe

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top