Bengt
Junior Member level 1
Signal filter L or R
I am about to design in a filter on the RS232 signal lines from a Bluetooth module and other circuit. The purpose is to avoid the noise from the module. The RS232 is communicating in 230 kbit. It is a space critical application so the components must be small, 0402 or 0603 size.
There are some alternatives
1. Series resistors. I know that 10 k works fine with the same circuits and signal speed.
2. I can replace the resistors with multi layer chip inductors.
3. I can combine any of the above method with a capacitor to GND to form a well defined LP filter.
The draw back of 3 is size, nothing else (I think). But what about R or L? A chip inductor is a wide band EMC surpressign component but it will never have such a high impedance as 10k for any freqvens. For low frequencys the inductor will have just a few ohms. But how do a resistor work at higher frequencies? There is not much about this in the data sheets.
So, I understand that 3 may always be a good idea and also will have a better defined cut of frequency. The problem is to choose L or R.
I am about to design in a filter on the RS232 signal lines from a Bluetooth module and other circuit. The purpose is to avoid the noise from the module. The RS232 is communicating in 230 kbit. It is a space critical application so the components must be small, 0402 or 0603 size.
There are some alternatives
1. Series resistors. I know that 10 k works fine with the same circuits and signal speed.
2. I can replace the resistors with multi layer chip inductors.
3. I can combine any of the above method with a capacitor to GND to form a well defined LP filter.
The draw back of 3 is size, nothing else (I think). But what about R or L? A chip inductor is a wide band EMC surpressign component but it will never have such a high impedance as 10k for any freqvens. For low frequencys the inductor will have just a few ohms. But how do a resistor work at higher frequencies? There is not much about this in the data sheets.
So, I understand that 3 may always be a good idea and also will have a better defined cut of frequency. The problem is to choose L or R.