Hi I was wondering if anyone would have some advice for the following problem:

I have 4 PWM signals that I want to convert to analog voltage signals.

I realise I can use a simple LP filter to change the PWM signal into a voltage,

the only problem is that the Peak to Peak of the 4 PWM signals is slightly different (but ideally should be the same).

However, the duty cycle of each PWM is very accurate so I would like to find a way to convert the duty cycle of each PWM into a 0.7 to 5V signal.


Could I use a transistor as a switch (or somesort of electronic switch), to get consistent p-p PWM signals, then just use a LP filter?

Any suggestions would be appreciated.


Thanks

 

What is the level of the existing PWM signals? Is it above the 5 volt level? If so, you could use 5 volt zeners with limiting resistors to limit the voltage to 5V/0V levels and use the LP filter to develop the variable voltage.

 

Pass the PWM signals through a buffer and you will then have isolation, buffering and exactly equal output PWM signal level.

 

The buffer idea is good, like using a CMOS hex buffer IC.

But this might be simpler; instead of just using a RC lowpass filter, use a RC+R where the 2 resistors form a voltage divider. If you make one of the resistors a trimpot you can adjust the DC output voltage to calibrate it.

At the very simplest level you only need 4 trimpot and 4 caps, but you probably will want finer calibration control so that's 4R 4C 4trim etc.