AD8611 comparator at 60 MHz

Question

I'm trying to process a sinusoidal signal into a square wave at frequencies above 1 MHz. This is my first time doing this so it doesn't work properly. If anyone can help with an explanation, I would greatly appreciate it.

This is the circuit:

AD8611 datasheet

According to datasheet this comparator should operate on frequencies upto 100 MHz.

At frequencies 1 MHz - 10 MHz everything seems to be fine.

The waveforms look like this:

The higher the frequency, the less the output on the comparator resembles a square wave:

This is how it should be, but I still want to ask for advice.

Am I doing everything right? How can I improve this circuit?

The comparator is designed for frequencies up to 100 MHz, but above 10 MHz the square wave begins to lose its shape.

The output of the comparator will be fed to the bipolar transistor.

The probe for the output is set to 10X, the probe for sine wave still in 1X poistion. Here are the udpdated screens:

Now it looks more realistic.

Answer 1

Since both waveforms are BW limited, the biggest problem is the 1:1 probe and perhaps the DSO BW.

Checklist for 100 MHz output

1. Low ource impedance low (<=400 Ohms)

2. Low pF probe (10:1 only, calibrated on square)

3. Short probe ground (< 2cm or tip & ring only)

4. Short traces from output and ground

5. Decoupling cap <= 1cm from IC.

6. DSO not limited by 20MHz filter and pref. Rated for >=-300 MHz.

7. Expect prop delay and risetime to meet spec. If all other conditions satisfy datasheet.

8. don't expect textbook squarewaves on your 1st design, that might require CML or ECL logic comparators to include at least 7th harmonic.