Continue to Site

Welcome to

Welcome to our site! 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.

oscilation at 75175 output - how to prevent ?

Not open for further replies.


Full Member level 4
Jan 10, 2009
Reaction score
Trophy points
Istanbul , Turkey
Activity points
hello forum

in my servo driver project I am taking encoder signals A A* B B*
with 75175 and counting the output with microcontroller

however as shown in attached picture at the 75175 output
at the falling edge there occurs oscilation

this causes sometimes miscounting of encoder position
power supply is LM2575 and there is 100 nF bypass at power pins of 75175

my question how can I prevent this ?
thank you

Looks like unsuitable circuit layout. A series resistor at the output (e.g. 100 ohm) can most likely dampen the oscillations.
Last edited:
hello ,

I have found the problem
this is my servo driver project
I have observed the voltage between the motor PE cable ( connected to motor chasis )
and the uC board GND with oscilloskop

there are 100 V peaks every 100 uS ( my PWM frequency is 10 KHz )

this time I connected motor PE and uC board GND with a 1 mm2 cable ( about 10 cm ) and this conected to P.Earth of the shop
I again observed the voltage between the GND of uC board and the connection point to PE of motor ( 10 cm away from board )
there were 2 V oscillation every 100 uS

I mean there are about 2 V oscillation between the two end of 1 mm2 cable ?
how can this be ?

now I understand why they use multi layer boards in professional servo drives :-(
now what else can I do ?
thank you

To me it looks like you are get the high motor current flowing through the signal ground of the motor encoder generating the A/B incremental pulses. It should to be connected only with the control electronic ground and supply. The ground connection of the motor and the electronic should be a star connection. Maybe you need to think about a separate power supply for the motor encoder + control and the motor. Another option is to look for single chip encoder who delivers also the absolute information ( like in this application: ).

Enjoy your design work!

Not open for further replies.

Part and Inventory Search

Welcome to