Hello ,
I'm trying to interface a 5000 pulse per revolution rotary encoder to a microcontroller , the encoder output is a square wave (logic 0 : 0v , logic 1 : 12v) , i need to clip this signal to 5v for the microcontroller , the frequency of the encoder signal is up to 300 KHz (depending on the encoder rotation speed) .
the encoder outputs two signals (as the figure shows) , at the positive edge of signal A , I check on the value of signal B , if its 1 it means the encoder is revolving in one direction , if it is 0 , it is revolving in the other direction , and according to that i can increment or decrement the value of the variable (in the mc) representing the angular displacement of the encoder.
i first used a fast mosfet (2n7000) to do the clipping (Figure 2) , its on-time and off-time is 10ns , i tested it , it works well in low frequencies , but when the frequency exceeds 70KHz , the counting variable starts decreasing while the encoder is revolving in the positive direction , which means that at the positive edge of the signal A , B is 1 , but it was read as zero , because the switching is not fast enough .
this limits the speed of the encoder to a lower value than it can .
i then thought about using the zener clipping circuit(Figure 2) , but i read that zener clipping circuits are also not reliable in high frequencies .
is there a better way to clip high frequency signals (300KHz)
thanks very much
I'm trying to interface a 5000 pulse per revolution rotary encoder to a microcontroller , the encoder output is a square wave (logic 0 : 0v , logic 1 : 12v) , i need to clip this signal to 5v for the microcontroller , the frequency of the encoder signal is up to 300 KHz (depending on the encoder rotation speed) .
the encoder outputs two signals (as the figure shows) , at the positive edge of signal A , I check on the value of signal B , if its 1 it means the encoder is revolving in one direction , if it is 0 , it is revolving in the other direction , and according to that i can increment or decrement the value of the variable (in the mc) representing the angular displacement of the encoder.
i first used a fast mosfet (2n7000) to do the clipping (Figure 2) , its on-time and off-time is 10ns , i tested it , it works well in low frequencies , but when the frequency exceeds 70KHz , the counting variable starts decreasing while the encoder is revolving in the positive direction , which means that at the positive edge of the signal A , B is 1 , but it was read as zero , because the switching is not fast enough .
this limits the speed of the encoder to a lower value than it can .
i then thought about using the zener clipping circuit(Figure 2) , but i read that zener clipping circuits are also not reliable in high frequencies .
is there a better way to clip high frequency signals (300KHz)
thanks very much
