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RE: Help with ADCMP553


I am working on project where i am using a sine wave oscillator which gives output frequency of 200 to 250 MHz with Vp-p voltage of 500mV to 1000mV. I need to convert this sine wave to squarewave. So i chose to use ADCMP553 comparator.

I connected the output of oscillator with capacitive coupling and 50 Ohm load resistor. I connected the output across load resistor to non inverting input of comparator and the inverting input is connected to 50 Ohms to ground (zero threshold, though offset voltage is 10mV). I terminated the output in ac coupling of PECL termination for clock operation.

The problem is that the output from the comparator is not a square wave.

I am using 5 V supply to the comparator and in compare mode. Do i need to reference the inputs to Vcc-2 to make them input signals to PCEL?. I tried this also using 82 ohm and 130 Ohm divider referenced to VCC, so the signal offsets by VCC-2. Still i get sine wave output, but not square wave.

I don't know what else to do. Looking for some suggestions

  • Hi Vamsee_27,

    You should set a reference voltage at the inverting input. this voltage should be in the area of your input swing, if you what a 50% duty cycle you can set the reference voltage to 750mV, please be reminded though that input offset voltage could slightly affect the duty cycle by a small percentage.