AD652 output frequency is not stable or freezes for some voltage

Hello anybody,

     I am playing with AD652 for just demonstration use as simple AD converter for AT89S2051 (counting pulses during solid time first and in second one maybe measure time between two pulses). I connected it in breadboard like figure 8, providing dual supply by two linear ICs 7815 and 7915 and from 7815 also providing +5V by 7805 for digital supply of AD652 and also for microcontroller in future. But today I have seemed some surprise how circuit work.

Everything is like in figure 8 in AD652 datasheet, I am using 20 nF capacitor as integral capacitor between pins 4 and 5 and internal resistor 20 kiloohms, pull-up RL is 1.2 kiloohms. As clock I use generator Rigol DG1022 with square wave output 0-5V and testing some frequencies, voltage source is also this arbitrary generator using only DC offset generation from arbitrary waveforms category. Full scale of AD652 in this circuit may be 0-10V and frequency of clock can be up to 4 MHz if I read the datasheet correctly.

So what I am doing incorrect, if I use clock 10 kHz and then I rise up voltage and for some voltages between 3V and 9V the output frequency is not stable and swings so much. 0 VDC = 0 kHz with logical 1 on output, 10 VDC = 5 kHz, for 9 VDC its looks like on image.

If I use only 1 kHz frequency, then the input voltage from 3 VDC to 6 VDC gives 333 Hz square output and from 7 VDC to 10 VDC gives 500 Hz square output and between these values the output frequencies are the same.

Can anybody tell me, what I missed or overlook?

Thanks anybody in advance for answer and time

Best regards

Josef Kiefmann