Cannot get the correct signal waveform on ADCLK905 outputs

Hello. In a question I sent time ago about ADF4158 and low frequencies, there was an answer with a reference to circuit note CN-0290.

I have built a test board to check it  (I almost mimic all the circuitry in figure 2 of the circuit note), but the output signal is not as expected. Instead of having a square signal as in figure 7 of the datasheet, what I have is the same input signal but with less voltage level.

The input signal is a sine wave coming from a VCO and it has not a very high level (less than 0.2 V peak to peak). Wiring the VCO directly to the ADCLK905, the output is a sine wave.

In order to increase the input level, I added a amplifier to have more input level (up to 2.7V) but the output is the same: a sine wave.

What am I doing wrong? Why cannot get the square wave at the outputs?

See attached the schematics of the test board and the input and output signals I get.

Thanks in advance

  • 0
    •  Analog Employees 
    on Nov 25, 2020 4:55 PM


    I took an ADCLK905 evaluation board and I supplied at D1 terminal a sinusoid from a Rohde $ Schwarz SMA 100A, 30.72MHz, 6dBm.

    I configured the board as your circuit (VCC=3.3V, VEE=GND, VT1 and VREF1 connected together).

    I obtained a nice digital output: Channel 1, yellow is Q1, Channel 3, blue is the input at D1.

    Try reducing the frequency to ensure the oscilloscope probes do not attenuate the clocks. Then you can increase back the frequency. I input 200MHz and I still got rectangle output