Capacitor array in Oscillator

[transign]

Hello ,
I have created a capacitor array and each bit should offer 130MHz step.I observe that after turning on several bits for the capacitor array, the frequency step decreases and becomes less than 120 MHz, why could this happen? All the capacitor and switches have the same size.
Thanks!

 

[dick_freebird]

Parallel capacitors and parallel resistors have a
non-linear bit-weight even if all bits are same
weight. It's the parallel-value math.